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Use the arrangement of atoms suggested in the skeleton structure above to construct the Lewis structure for the SO$_3$ molecule. Which of the following statements about this molecule is incorrect?
A. Sulfur trioxide has three resonance structures.
B. Sulfur trioxide has a planar triangle shape.
C. Sulfur trioxide is nonpolar.
D. The S–O bond order is 5/3.
|
D Since the Lewis structure shows three bonding domains and four bonds, three sigma and one pi, the bond order is 4/3, not 5/3.
|
Chemistry/86
|
Chemistry
| null |
Use the arrangement of atoms suggested in the skeleton structure above to construct the Lewis structure for the sulfite ion. Be sure to minimize the formal charges. Which of the following statements is incorrect?
A. The sulfite ion has a double bond.
B. The sulfite ion has a triangular pyramid shape.
C. The sulfite ion is nonpolar.
D. The S–O bond order is 4/3.
|
C The sulfite ion has an unsymmetrical triangular pyramid structure and must be polar.
|
Chemistry/87
|
Chemistry
| null |
Ethanoic acid (\ce{HC2H3O2} \quad \text{or} \quad \ce{CH3CO2H} \quad \text{or} \quad \ce{CH3COOH}
) has a much lower vapor pressure than ethanol (\ce{CH3CH2OH}). What is the most reasonable explanation?
A. The polarizability of two oxygen atoms increases the London forces of attraction in ethanoic acid compared with ethanol.
B. Hydrogen bonding in ethanoic acid is the strongest attractive force and is mainly responsible for the observed data.
C. Ethanol has an –OH group and can hydrogen bond; therefore, the London forces must cause the effect.
D. Both ethanol and ethanoic acid have an –OH, so the difference is the dipole of the second oxygen that increases the attractive forces.
|
B Ethanoic acid molecules strongly hydrogen bond so that most molecules are part of dimers.
|
Chemistry/88
|
Chemistry
| null |
Vitamin C is oxidized slowly to dehydroascorbic acid by the oxygen in air. It is catalyzed by ions such as \ce{Cu^2+} and \ce{Fe^3+}
. The reaction can be followed by measuring the ultraviolet absorbance at 243 nm.
Which of the following is the best interpretation of the data given above?
A. The data support a first-order reaction.
B. The data support a second-order reaction.
C. The data support a zero-order reaction.
D. The overall order is 14.
|
A The data show a linear trend for ln A vs. time. This is characteristic of a first-order reaction.
|
Chemistry/89
|
Chemistry
| null |
Choose the description of the point on the distribution curve that is the most plausible.
A. Point A represents absolute zero where all motions stops.
B. Point C is proportional to temperature
C. Point B is where the transition state occurs.
D. At point D, the products of the reaction are found.
|
B At point C, which is a little beyond the maximum, the average kinetic energy is directly proportional to temperature.
|
Chemistry/89
|
Chemistry
| null |
Three 1-liter flasks are connected to a 3-liter flask by valves as shown in the diagram above. The 3-liter flask has the relative number of helium atoms as indicated. At the start, the entire system is at 585K. The first flask contains oxygen; the second contains hydrogen, and the third contains nitrogen. The pressure of hydrogen is 3.00 atm. The number of gas molecules is proportional to their representations in the flasks. If the valves are all opened, what will be the pressure in the system? Assume the connections have negligible volume.
A. 1.0 atm
B. 2.0 atm
C. 3.0 atm
D. 4.0 atm
|
B 6 particles is equivalent to 3 atmospheres. We have 24 particles and 6 liters, or 4 particles per liter. That is 4/6 or 2/3 of the original pressure, or 2.0 atm.
|
Chemistry/90
|
Chemistry
| null |
A mass spectrum of a naturally occurring sample of an element is shown above. What is the element?
A. Cl
B. S
C. Ar
D. There are two peaks, so there must be two compounds.
|
A Mass 35 is about 75 percent and mass 37 is about 25 percent. Calculate
\(0.75 \times 35 + 0.25 \times 37 = 26.25 + 9.25 = 35.5\)
This mass is very close to that of chlorine.
|
Chemistry/91
|
Chemistry
| null |
In the diagram above, which labeled arrow is pointing toward a covalent bond and which is pointing toward a hydrogen bond?
A. 1 2
B. 2 1
C. 3 4
D. 4 3
|
D Traditionally, solid lines indicate covalent bonds and dashed lines indicate attractive or repulsive interactions.
|
Chemistry/92
|
Chemistry
| null |
Space-filling representations of carbon tetrachloride and carbon tetrabromide are shown above. The carbon can be seen in the carbon tetrachloride and is hidden by the bromine in carbon tetrabromide. Which of the following is the most reasonable statement? (Assume that the temperatures of CCl$_4$ and CBr$_4$ are the same in these comparisons.)
A. CCl$_4$ has a higher surface tension compared with CBr$_4$
B. CCl$_4$has a higher vapor pressure compared with CBr$_4$.
C. CCl$_4$ has a higher boiling point compared with CBr$_4$.
D. CCl$_4$ has a higher viscosity compared with CB$_4$.
|
B We can deduce that the attractive forces in CBr$_4$ are stronger than those in CCl$_4$ because the bromine electron cloud is much more polarizable than the chlorine atom's electron cloud. Response (B) is the only one that agrees with the attractive forces.
|
Chemistry/93
|
Chemistry
| null |
Which of the labeled arrows in the diagram above represents the strongest intermolecular force of the four indicated?
A. Arrow A
B. Arrow B
C. Arrow C
D. Arrow D
|
A This represents an ion-dipole force, which is stronger than a hydrogen bond (B), a dipole-dipole force (C), or a London dispersion force (D).
|
Chemistry/94
|
Chemistry
| null |
According to the data in the table above, which of the compounds has the strongest intermolecular forces?
A. Propylamine
B. Ethyl methyl ether
C. Trimethyl amine
D. Ethyl methyl amine
|
A The compound with the highest boiling point has the strongest intermolecular forces. This is only valid if the molar masses are similar.
|
Chemistry/95
|
Chemistry
| null |
Each of the ions in the table form stable oxides (Na$_4$O, CdO, and La$_4$O$_3$). Lanthanum oxide, La$_4$O$_3$, has a melting point significantly higher than that of the other oxides. Which of the following is the best explanation of why this is true?
A. Lanthanum is a lanthanide element and the melting points of these elements are always high.
B. There is more oxygen in the formula La$_4$O$_3$ than in the other formulas.
C. Lanthanum had the highest charge; therefore, it has the highest lattice energy.
D. Alkali metals like sodium and transition metals like cadmium tend to have low melting points.
|
C The melting points of ionic materials depend upon the lattice energy. The higher the lattice energy, the higher the melting point is. Lattice energies depend upon the sizes of the ions and the magnitude of the charge. All three metal ions are approximately the same size; therefore, the size factor is minimal. This leaves the magnitude of the charge, and lanthanum, with the largest charge, should have the highest lattice energy.com/ap/chemistry/question-479-answer-and-explanation.html
|
Chemistry/96
|
Chemistry
| null |
The diagram above shows the structure of molecules of CS$_2$ and COS. The boiling point of COS is 223 K, and the boiling point of CS2 is 319 K. Which of the following is the best explanation of why the boiling point of CS$_2$ is higher?
A. The molar mass of CS$_2$ is greater.
B. COS has weaker covalent bonds than CS$_2$.
C. Only CS$_2$ can form intermolecular dipole-dipole forces.
D. COS has stronger intermolecular forces because it is polar and CS$_2$ is not.
|
A-Stronger intermolecular forces lead to higher boiling points. Even though COS has dipole-dipole forces, which are usually stronger than the London dispersion forces present in CS$_2$, the greater molar mass of CS$_2$ leads to a London dispersion force contribution that is sufficient to compensate for the general trend of dipole-dipole forces being stronger than London dispersion forces. This is why comparisons should only be made between molecules of similar molecular masses.
|
Chemistry/97
|
Chemistry
| null |
Which of the labeled arrows in the diagram above represents the strongest intermolecular force?
A. A
B. B
C. C
D. D
|
B This is a dipole-dipole force, which is stronger than a dipole-induced dipole (A and C) or a London dispersion force (D).
|
Chemistry/98
|
Chemistry
| null |
A dimer consists of two closely associated molecules. In the gas phase, acetic acid tends to form dimers as illustrated on the left in the above diagram. Acetyl chloride, on the right in the above diagram, is not very efficient in forming dimers. Why is acetic acid better able to form dimers than acetyl chloride?
A. The molecular mass of acetyl chloride is higher than that of acetic acid making it harder for the acetyl chloride to form dimers.
B. It is easier to form a covalent bond between acetic acid molecules than between acetyl chloride molecules.
C. Acetic acid can form strong hydrogen bonds but acetyl chloride can only form weaker dipole-dipole attractions.
D. Acetic acid is an acidic compound but acetyl chloride is a neutral compound.
|
C The two molecules are hydrogen bonded together. Hydrogen bonding is a relatively strong intermolecular force. Acetyl chloride cannot exhibit anything stronger than dipole-dipole forces, which are, in general, weaker than hydrogen bonds.
|
Chemistry/99
|
Chemistry
| null |
Which of the compounds in the above diagram is capable of participating in hydrogen bonding?
A. C$_3$H$_9$ N
B. CH$_3$F
C. C$_2$H$_6$O
D. C$_4$H$_11$
|
D-Hydrogen bonding is possible when hydrogen is attached to N, O, and F. D is the only compound in the diagram where this is true. The simple presence of hydrogen and N, O, or F is insufficient.
|
Chemistry/100
|
Chemistry
| null |
In the diagram above, which labeled arrow is pointing toward a hydrogen bond?
A. 1
B. 2
C. 3
D. 4
|
C Dashed lines traditionally represent attractions that are NOT covalent bonds. In this case, they represent hydrogen bonds.
|
Chemistry/101
|
Chemistry
| null |
The graph above shows the distribution of kinetic energies of a large number of Ne atoms at 500 K. Which letter shows the average kinetic energy of this system?
A. A
B. B
C. C
D. D
|
C Slightly to the right of the maximum of the distribution curve is the average kinetic energy.
|
Chemistry/102
|
Chemistry
| null |
The above graph shows a titration curve of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.075 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the graph. Which arrow points to the end point of this titration?
A. A
B. E
C. C
D. F
|
B Point E is the inflection point that represents the end point.
|
Chemistry/103
|
Chemistry
| null |
The above graph shows a titration curve of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.075 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the graph. Which arrow points to the place on the curve where the pH is equal to 14 - pK$_b$?
A. A
B. E
C. C
D. F
|
C Point C is the midpoint of the titration. At this point, the pOH = pK$_b$. The pOH = 14 - pH. So 14 - pH = pK$_b$, and this rearranges to the equation shown in the question.
|
Chemistry/104
|
Chemistry
| null |
The Lewis diagram for nitric acid, $HNO_3$, is above. Which of the following statements is true regarding nitric acid?
A. $HNO_3$ molecules are planar.
B. The nitrogen atom carries a negative formal charge.
C. All N-O bonds are of identical length.
D. There is a third equivalence resonance structure that is not shown.
|
A The resonance shown here is for the $N-O$ bonds that do not have hydrogen attached on the other end of the oxygen. This means that two of the $N-O$ bonds are identical (bond order = 1.5), but the third one (from $N-O-H$) is a true single bond. The geometry around the $N$ is trigonal planar, and the geometry around the $O$ in the $N-O-H$ is bent, both of which are planar geometries.
|
Chemistry/105
|
Chemistry
| null |
The photoelectron below spectrum is for a neutral fluorine atom. Compared to that spectrum, the spectrum for a fluoride ion would have
A. one more peak
B. one less peak
C. the same number of peaks, but the rightmost peak would be taller
D. the same number of peaks, but the leftmost peak would be taller
|
C A fluoride atom is $[He]2s^22p^5$. A fluorine ion would be $[He]2s^22p^6$. The $2p$ peak is the rightmost peak, and in the ion it would contain one more electron and thus be higher than the $2p$ peak from the neutral atom.
|
Chemistry/106
|
Chemistry
| null |
A student is attempting to use a distillation apparatus, shown below, to separate a mixture of propanol (boiling point: 97°C) and propionic acid (boiling point: 141°C). Which temperature should the apparatus be set at to obtain as pure a distillate of propanol as possible?
A. 85°C
B. 105°C
C. 125°C
D. 145°C
|
B In order to separate out the propanol, it must be boiled, so the temperature must be above the boiling point of propanol. However, the temperature should also be below the boiling point of propionic acid, because if both substances boil, they will not separate effectively. There are two options in the temperature range, and the lower one is better because the propionic acid will have a lower vapor pressure at 105°C, meaning less of it will evaporate and contaminate the distillate.
|
Chemistry/107
|
Chemistry
| null |
Given the half-reactions below, what would the coefficient on the $NO(g)$ be when the full reaction below is balanced?
A. 1
B. 2
C. 3
D. 4
|
B To fully balance the reaction, the charge must be balanced. This required multiplying the zinc oxidation half-reaction by two, and the nitrate reduction half-reaction by three. Doing that and combining the reactions yields: $3Zn (s) + 8H^+ (aq) + 2NO_3^- (aq) \rightarrow 2NO (g) + 4H_2O (l) + 3Zn^{2+} (aq)$
|
Chemistry/108
|
Chemistry
| null |
A Lewis diagram of the hydrogen phosphate ion is shown below. Based on this diagram, which of the atoms would have a negative formal charge?
A. P
B. Ox
C. Oy
D. Oz
|
D Formal charge is calculated by subtracting the number of assigned electrons on an atom in a Lewis diagram from the number of its valence electrons. When looking at an atom, lone pairs are considered to be two assigned electrons, and any type of bond is considered to be one (so a single bond is one, a double bond would be two, etc). Constructing a formal charge chart for the identified atoms shows that of the identified atoms only $Oz$ would have a negative formal charge. https://img.apstudy.net/ap/chemistry/cr20/0445_Image_0002.jpg
|
Chemistry/109
|
Chemistry
| null |
The $K_a$ values for three different weak acids are given below. If the acid is polyprotic, all of the $K_a$ values for that acid are given. If each acid were to be titrated with 0.10 M NaOH, which solution would have the highest pH at the endpoint of the titration when each acid has fully reacted?
A. Formic
B. Sulfurous
C. Citric
D. All titrations would have identical pHs at the endpoint.
|
B After all of an acid has reacted during a titration, all that is present in the solutions is the conjugate base of that acid. In a polyprotic titration, the endpoint occurs after all of the protons have been neutralized. In each case, the lower the $K_a$ is for the final dissociation of the weak acid, the higher the $K_b$ will be of its conjugate base (because for any conjugate pair, $K_a \times K_b = 1.0 \times 10^{-14}$). A higher $K_b$ means a stronger conjugate base, leading to a higher pH at the endpoint.
|
Chemistry/110
|
Chemistry
| null |
A piece of potassium metal is added to a solution of hydrochloric acid, and the metal starts to react. Which of the following is the correct net ionic equation for the reaction that is occurring?
A. $2H^+(aq) + K^+(aq) + 3e^- \rightarrow H_2(g) + K(s)$
B. $2H^+(aq) + 2K^+(aq) + 4e^- \rightarrow 2K(s) + H_2(g)$
C. $2H^+(aq) + K(s) \rightarrow K^+(aq) + H_2(g)$
D. $2H^+(aq) + 2K(s) \rightarrow 2K^+(aq) + H_2(g)$
|
D The $H^+$ ions are being reduced, but the $K (s)$ is being oxidized, so the potassium half-reaction has to be flipped. It also has to be multiplied by two so the electrons will cancel out when the two half reactions are combined.
|
Chemistry/111
|
Chemistry
| null |
The Lewis diagram of the bisulfite ion, $HSO^{3-}$, is drawn below. Which of the following descriptions correctly compares the bond lengths of the three sulfur-oxygen bonds found in bisulfite?
A. All bonds are the same length.
B. Of the three bonds, there is one longer one and two shorter ones of identical length.
C. Of the three bonds, there are two longer ones of identical length and one shorter one.
D. All three bonds are different lengths.
|
B There is resonance between the two $S-O$ bonds where the $H$ is not attached to the other side of the oxygen atom. These bonds are identical in length, but would be shorter than the true single $S-O$ bond with the oxygen that does have the hydrogen bonded to it.
|
Chemistry/112
|
Chemistry
| null |
A sample of hydrogen peroxide, $H_2O_2$, will decompose over time. The graph below charts the concentration of an $H_2O_2$ sample over time. What is the rate law for the overall reaction?
A. Rate = k
B. Rate = k[$H_2O_2$]
C. Rate = k[$H_2O_2$]2
D. Rate = k[$H_2O$][$O_2$]
|
B The graph indicates the decomposition reaction has a constant half-life. This means the reaction must be first order.
|
Chemistry/113
|
Chemistry
| null |
A semiconductor with a silicon lattice is doped by the addition of another element, symbolized by the letter X in the diagram below. Which of the following statements best describes the possible identity of the element as well as the type of doping that is occurring?
A. Boron, which has less valence electrons than silicon and creates positive "holes" in the lattice
B. Phosphorus, which has extra valence electrons and creates a mobile negative charge in the lattice
C. Aluminum, which has metalloid properties that lend to increased conductivity when added to a semiconductor
D. Carbon, which has an equal number of valence electrons as silicon and strengthens the conducting lattice
|
A Element X only forms three bonds with the surrounding silicon atoms, meaning it only has three available valence electrons to form bonds. That is consistent with boron, and adding boron into a silicon lattice is called p-doping, which involves creating positive areas for any mobile electrons to be attracted to.
|
Chemistry/114
|
Chemistry
| null |
Given the bond enthalpy values in the data table below, determine the enthalpy change for the reaction above it.
A. -1220 kJ/mol
B. -400 kJ/mol
C. 400 kJ/mol
D. 1220 kJ/mol
|
A When determining the enthalpy of reaction using bond enthalpies, bonds broken in the reactants are assigned a positive value and bonds formed in the products are assigned a positive value prior to summing them all up. Remember to account for both the number of bonds inside a molecule as well as how many of that molecule there is in the balanced equation when calculating (for instance, there are 4 $H-O$ bonds in 2 $H_2O$ molecules). 4($C-H$) + ($C=C$) + 3($O=O$) - 4($C=O$) - 4($H-O$) = $\Delta H_{rxn}^{\circ}$ 4(410) + 720 + 3(500) - 4(800) - 4(470) = -1220 kJ/mol
|
Chemistry/115
|
Chemistry
| null |
$[NO]$ (M) $[O_2]$ (M)
The reaction below is run with the concentration of both reactants at 0.10 M. Which of the following values for the initial concentration of both reactants would lead to an initial reaction rate which is double that of the first trial?
A. 0.15 0.15
B. 0.20 0.20
C. 0.20 0.050
D. 0.050 0.20
|
C The reaction is second order with respect to NO. This means doubling the concentration of NO will make the reaction go four times faster. At the same time, given that the reaction is first order with respect to O2, cutting the concentration of O2 in half will halve the speed of the reaction. Combining both factors yield $4 \times 0.50 = 2$.
|
Chemistry/116
|
Chemistry
| null |
Two batteries are constructed via the diagram below. The concentration of the solutions and the mass of the electrodes are identified in the data below the diagram. How would the voltage and the battery life for the two batteries compare?Voltage Battery Life
A. X <Y X <Y
B. X <Y X =Y
C. X =Y X = Y
D. X =Y X < Y
|
D Voltage is a function of the reaction quotient for the battery. Given that $Q = [Zn^{2+}]/[Cu^{2+}]$, in both batteries the value for Q would be the same, making their voltages the same. However, battery Y has more metal ions both in solution and in the electrodes, meaning the battery could operate for longer.
|
Chemistry/117
|
Chemistry
| null |
$Cu^{2+}$ ions appear blue in solution, and the $NO_3^-$ ion is colorless. The absorbance of a $Cu(NO_3)_2$ solution is measured at various wavelengths using a spectrophotometer. To determine the concentration of a $Cu(NO_3)_2$ solution of unknown concentration, what wavelength of light would produce the best results?
A. 350 nm
B. 500 nm
C. 640 nm
D. 800 nm
|
C The maximum absorbance of the copper ion occurs at approximately 640 nm. When studying a copper solution of unknown concentration, comparing it to a Beer's Law plot constructed at an absorbance of 640 nm would create the greatest possible absorbance range and give the best results.
|
Chemistry/118
|
Chemistry
| null |
The diagram below supports which of the following conclusions about the reaction shown below?
A. There is an increase in entropy.
B. Mass is conserved in all chemical reactions.
C. The pressure increases after the reaction goes to completion.
D. The enthalpy value is positive.
|
B The amount of matter is equal on both sides of the reaction. None of the other options are supported by the diagram.
|
Chemistry/119
|
Chemistry
| null |
Ox N Oy
One of the resonance structures for the nitrite ion is shown below. What is the formal charge on each atom?
A. -1 +1 -1
B. +1 -1 0
C. 0 0 -1
D. -1 0 0
|
D Ox has 6 valence electrons and 7 assigned electrons: 6 - 7 = -1. Both Oy and the N atoms have the same number of valence and assigned electrons, making their formal charges zero.
|
Chemistry/120
|
Chemistry
| null |
Identify the three gases represented on the Maxwell-Boltzmann diagram below. Assume all gases are at the same temperature.I II III
A. $H_2$ $N_2$ $F_2$
B. $H_2$ $F_2$ $N_2$
C. $F_2$ $N_2$ $H_2$
D. $N_2$ $F_2$ $H_2$
|
C At identical temperatures, the gases would all have identical amounts of kinetic energy. In order for that to happen, the gas with the lowest mass ($H_2$) would have to have the highest average velocity, and the gas with the highest mass ($F_2$) would have to have the lowest average velocity.
|
Chemistry/121
|
Chemistry
| null |
If the $H_2C_2O_4$ were to be replaced with an identical volume of $H_2SO_4$, what volume of $NaOH$ would be required to fully neutralize the acid?
A 0.10 M solution of $NaOH$ is titrated into 20 mL of $H_2C_2O_4$, a diprotic acid, of an unknown concentration. The pH of the $H_2C_2O_4$ solution is monitored as the $NaOH$ is added to it, resulting in the below graph.
A. 10 mL
B. 20 mL
C. 40 mL
D. 60 mL
|
B The strength of the acid is irrelevant. $H_2SO_4$ has the same number of protons as $H_2C_2O_4$, and thus it will require the same amount of base to fully neutralize.
|
Chemistry/122
|
Chemistry
| null |
5mL 15mL 25mL
Phenolphthalein is an acid-base indicator with a pKa of 9.1. Its protonated form is often abbreviated as $HIn$, while its conjugate base is abbreviated as $In^-$. At the following volumes of NaOH added, select the option that accurately describes which form of the indicator will be present in a greater concentration.
A 0.10 M solution of NaOH is titrated into 20 mL of $H_2C_2O_4$, a diprotic acid, of an unknown concentration. The pH of the $H_2C_2O_4$ solution is monitored as the NaOH is added to it, resulting in the below graph.
A. $HIn$ $HIn$ $In^-$
B. $HIn$ $In^-$ $In^-$
C. $In^--$ $In^-$ $HIn$
D. $In^-$ $HIn$ $HIn$
|
A Below a pH of 9.1, the predominant form of the indicator will be its protonated state, $HAc$. Above 9.1, there will be more of the conjugate base, $Ac^-$.
|
Chemistry/123
|
Chemistry
| null |
At the point at which 20 mL of NaOH has been added, which of the following species is present in the greatest concentration in solution?
A 0.10 M solution of NaOH is titrated into 20 mL of $H_2C_2O_4$, a diprotic acid, of an unknown concentration. The pH of the $H_2C_2O_4$ solution is monitored as the NaOH is added to it, resulting in the below graph.
A. $H^+$
B. $OH^-$
C. $HC_2O_4^-$
D. $C_2O_4^{2-}$
|
D At a volume of 20 mL, the $OH^-$ has fully reacted with the $H_2C_2O_4$, removing all of its protons. Other than water, the only species present in significant concentrations at that point is the $C_2O_4^{2-}$.
|
Chemistry/124
|
Chemistry
| null |
What is the concentration of the $H_2C_2O_4$ solution?
A 0.10 M solution of NaOH is titrated into 20 mL of $H_2C_2O_4$, a diprotic acid, of an unknown concentration. The pH of the $H_2C_2O_4$ solution is monitored as the NaOH is added to it, resulting in the below graph.
A. 0.025 M
B. 0.050 M
C. 0.10 M
D. 0.20 M
|
B 
|
Chemistry/125
|
Chemistry
| null |
Data considering the conductivity of four different substances in their various phases is given in the table below. Of the four options, which substance is most likely to be $NaCl$?
A. Substance A
B. Substance B
C. Substance C
D. Substance D
|
B Ionic substances such as $NaCl$ do not conduct electricity in their solid form, but do when melted and/or dissolved in water.
|
Chemistry/126
|
Chemistry
| null |
As shown below, four identical containers hold the same number of moles of four different gases at 298 K. If ideal behavior is NOT assumed, in which container would the pressure be the lowest?
A. $H_2O$
B. $CH_4$
C. $Ne$
D. $He$
|
A Gases deviate from ideal behavior when their IMFs are significant enough to affect their behavior. When IMFs cause gas molecules to attract each other, that means they will hit the sides of the container less often and decrease the pressure. In this case, $H_2O$ has the strongest IMFs due to hydrogen bonding, and thus $H_2O$ molecules are most likely to deviate from ideal behavior.
|
Chemistry/127
|
Chemistry
| null |
Based on the mass spectrum shown below, which of the following can be concluded about zirconium?
A. The most common charge on a zirconium ion is +2.
B. Zirconium nuclei can have different number of protons.
C. The average atomic mass of a zirconium atom is 90 amu.
D. The most common isotope of zirconium has 50 neutrons.
|
D From the graph, you can see that the most common isotope of zirconium has an atomic mass of 90. Atomic mass is equal to the number of protons plus the number of neutrons, and all zirconium atoms have 40 protons. 90 - 40 = 50 neutrons.
|
Chemistry/128
|
Chemistry
| null |
The system below is at equilibrium. If it were to be diluted, what would happen to the moles of reactants and the moles product after equilibrium is reestablished?Mole Reactants Moles Product
A. Increase Increase
B. Increase Decrease
C. Decrease Decrease
D. No Change No Change
|
B The reaction quotient is $Q = \frac{[Cu(NH_3)_4^{2+}]}{[Cu^+][NH_3]^4}$. Diluting the equilibrium will decrease the concentration of all ions by the same amount, but that will have a larger effect on the denominator in Q because there are more ions present. This, in turn, means Q will increase, causing a shift to the left, increasing the amount of reactants and decreasing the amount of products.
|
Chemistry/129
|
Chemistry
| null |
A sample of some $N_2O_5$ gas is placed in a sealed container and allowed to decompose. The concentration of the $N_2O_5$ is tracked over time, and the results are plotted on the above graph. Which of the following represents the possible units on the rate constant for this reaction?
A. $s^{-1}$
B. $sM^{-1}$
C. $Ms^{-1}$
D. $Ms^{-2}$
|
A The graph shows a constant half-life-that is, the concentration of the $N_2O_5$ decreases by half every 5 seconds. The rate law is thus rate = k[$N_2O_5$]; dimensional analysis gets us to the units on k: M/s = k(M). k = s$^{-1}$.
|
Chemistry/130
|
Chemistry
| null |
Vapor Pressure @ 25°C (torr)
Substance
Three different liquids are mixed together in a flask, and that flask is then hooked up to a distillation apparatus, as shown below. The liquids are initially at 25°C, and the heat is turned up until the mixture starts to boil. Which liquid would be the first to separate out of the mixture?
A. $H_2O$
B. $CH_3OH$
C. $C_6H_{12}$
D. Distillation would be an ineffective method of separating the mixture.
|
B Vapor pressure is inversely proportional with IMF strength, so the substance with the greatest vapor pressure (in this case, $CH_3OH$) would have the weakest IMF strength. That also means it has the lowest boiling point, and would boil first.
|
Chemistry/131
|
Chemistry
| null |
1.0 mole of $NO_2(g)$ is bubbled through excess water, causing the above reaction to take place. Which of the following statements correctly describes the energy change that will occur during the reaction?
A. 135 kJ of energy will be emitted.
B. 45 kJ of energy will be emitted.
C. 135 kJ of energy will be absorbed.
D. 405 kJ of energy will be absorbed.
|
B 1.0 mol $NO_2$ $\times$ https://img.apstudy.net/ap/chemistry/cr20/041_Image_0001.jpg = -45 kJ (the negative sign means energy is released).
|
Chemistry/132
|
Chemistry
| null |
A beaker is filled with some 1.0 M $CuSO_4$, and two carbon electrodes are placed in the beaker with a battery wired between them, as shown below. As current is run through the system, solid copper plates out onto the carbon cathode. Which of the following changes would increase the amount of solid copper that is plated out of solution?
A. Replacing the 1.0 M $CuSO_4$ solution with 1.0 M $CuCl_2$
B. Using a 9.0 V battery instead of a 1.5 V battery
C. Decreasing the pH of the solution
D. Changing out the carbon electrodes with platinum electrodes
|
B Using a battery with a larger voltage would lead to a larger current, which in turn would lead to a larger mass of copper being plated out of solution.
|
Chemistry/133
|
Chemistry
| null |
The photoelectron spectrum of an element is below. Based on the spectrum, what is the charge on the most common ion of the element?
A. -2
B. -1
C. +1
D. +2
|
D The PES represents an electron configuration of $1s^22s^22p^63s^2$ that of magnesium. When forming an ion, the most stable pathway is to lose the two electrons in the third energy level, giving the ion a charge of +2.
|
Chemistry/134
|
Chemistry
| null |
A beaker of saturated zinc iodate is left out overnight. The following morning, some water is found to have evaporated. Assuming the temperature remained constant at 25°C, which of the following options correctly identifies the changes in the $[Zn^{2+}]$ and the mass of the zinc iodate present in the beaker compared to the previous night?
Zinc iodate dissociates in water via the following equilibrium process $[Zn^{2+}]$ Mass Zn(IO3)2
A. Increase Decrease
B. Increase No Change
C. No Change Increase
D. No Change Decrease
|
C In a saturated solution, the concentration of each component ion will always remain constant. For that to happen if water evaporates, some ions must "fall" out of solution, increasing the total amount of precipitate.
|
Chemistry/135
|
Chemistry
| null |
Zinc iodate dissociates in water via the following equilibrium process. Which of the following solutions would zinc iodate be the LEAST soluble in?
A. 1.0 M BaCl2
B. 1.0 M NaIO3
C. 1.0 M K2CO3
D. Pure water
|
B Due to the common ion effect, zinc iodate would be least soluble in a solution with which it shared an ion. Of the options, only $NaIO_3$ shares an ion ($IO_3^-$) with $Zn(IO_3)_2$.
|
Chemistry/136
|
Chemistry
| null |
What is the approximate molar solubility of zinc iodate at 25°C?
Zinc iodate dissociates in water via the following equilibrium process
A. $1.0 \times 10^{-2}$ M
B. $2.0 \times 10^{-3}$ M
C. $4.0 \times 10^{-6}$ M
D. $1.0 \times 10^{-6}$ M
|
A $K_{sp} = [Zn^{2+}][IO_3^{-}]^2$ $4.0 \times 10^{-6} = (x)(2x)^2$ $4.0 \times 10^{-6} = 4x^3$ $1.0 \times 10^{-6} = x^3$ $x = 1.0 \times 10^{-2} M$
|
Chemistry/137
|
Chemistry
| null |
When the oxidation-reduction reaction below is completely balanced, what is the coefficient on the $MnO_4^-$ ion?
A. 1
B. 2
C. 3
D. 4
|
B The manganese goes from an oxidation state of +7 in $MnO_4^-$ to +2 in $Mn^{2+}$, necessitating a gain of 5 electrons. The carbon goes from an oxidation state of +3 in $C_2O_4^{2-}$ to +4 in $CO_2$, and in the balanced equation that would happen twice (i.e., a 2 coefficient is needed in front of the $CO_2$ to balance it), necessitating a loss of 2 electrons. To balance the charge, the manganese half-reaction must be multiplied by 2 while the carbon half-reaction is multiplied by 5.
|
Chemistry/138
|
Chemistry
| null |
The mass spectrum below shows the distribution of various isotopes of strontium. Based on the data, which of the following conclusions can be drawn?
A. Strontium most commonly forms ions with a charge of +2.
B. Strontium isotopes with a mass of 86 or 87 are very unstable.
C. The number of protons in a strontium atom nucleus can vary.
D. The most common isotope of strontium has 50 neutrons.
|
D The most common isotope of strontium has an atomic mass of 88, and a strontium nucleus has 38 protons. As atomic mass = protons + neutrons, that means the most common isotope of strontium must have 50 neutrons.
|
Chemistry/139
|
Chemistry
| null |
The Lewis diagrams for both ethanol and octane are drawn below. Ethanol's boiling point is 78°C, while octane's is 125°C. This is best explained by the fact that
A. octane has hydrogen bonding, while ethanol does not
B. octane has a significantly higher molar mass than ethanol
C. octane's temporary dipoles are stronger than those in ethanol
D. octane is more symmetrical than ethanol
|
C Ethanol displays hydrogen bonding, which is the strongest type of intermolecular force. However, London dispersion forces are based on the overall polarizability of a molecule's electron cloud, which in turn is based on the number of electrons that molecule has. Octane has significantly more electrons than ethanol, and the dispersion forces caused by that overwhelm even the hydrogen bonds in ethanol, causing octane to have a higher boiling point.
|
Chemistry/140
|
Chemistry
| null |
If a small, pinhole-size leak were to be drilled into each container, the container with which gas would experience the fastest pressure decrease?
10.0 g each of three different gases are present in three glass containers of identical volume, as shown below. The temperature of all three flasks is held constant at 298 K.
A. $SO_2$
B. $CH_4$
C. $NCl_3$
D. All three containers would decrease pressure at the same rate.
|
B The rate at which a gas effuses is inversely proportional with its molar mass. A gas with a lower molar mass (in this case, $CH_4$), will have molecules moving with a higher average velocity, meaning they are going to hit that hole more often and will be more likely to escape.
|
Chemistry/141
|
Chemistry
| null |
10.0 g each of three different gases are present in three glass containers of identical volume, as shown below. The temperature of all three flasks is held constant at 298 K.Which of the gases would have the greatest density?
A. $SO_2$
B. $CH_4$
C. $NCl_3$
D. All three gases would have the same density.
|
D Density is simply mass divided by volume. The mass and volume of each gas is identical; therefore, their densities are identical.
|
Chemistry/142
|
Chemistry
| null |
The container with which gas would have the greatest pressure?
10.0 g each of three different gases are present in three glass containers of identical volume, as shown below. The temperature of all three flasks is held constant at 298 K.
A. $SO_2$
B. $CH_4$
C. $NCl_3$
D. All four containers would have the same pressure.
|
B Pressure is directly related to the number of moles of a gas. $CH_4$ has the lowest molar mass out of the three gases, and therefore 10.0 grams of it represents the greatest number of moles, leading to the greatest pressure.
|
Chemistry/143
|
Chemistry
| null |
$SiCl_4$ $PCl_3$
The Lewis diagrams for $SiCl_4$ and $PCl_3$ are drawn below. What are the approximate bond angles between the terminal chlorine atoms in each structure?
A. 90 90
B. 109.5° < 109.5°
C. 90° 109.5°
D. < 109.5° > 90°
|
B Both molecules have four electron groups around the central atom, so their base geometry is tetrahedral, which has bond angles of 109.5°. However, the $PCl_3$ has a lone pair as well, which exerts a slightly greater repulsive force than a bonded pair, bringing the bond angles in that molecule to slightly less than the ideal 109.5°.
|
Chemistry/144
|
Chemistry
| null |
X Y Z
The formate ion, $HCO_2^-$, is best represented by the Lewis diagram below. Each bond is labeled with a different letter.What is the bond order for each bond?
A. 1 1 2
B. 2 2 1
C. 1 1.5 1.5
D. 1.33 1.33 1.33
|
C The $H-C$ bond is a single bond with a bond order of one. The $C-O$ bonds display resonance, and the average bond order between them is $(1 + 2)/1 = 1.5$.
|
Chemistry/145
|
Chemistry
| null |
Initial pH Equivalence pH Ending pH
A student titrates some 1.0 M $HCl$ into 20.0 mL of methylamine ($CH_3NH_2$), a weak base which only accepts a single proton. The following titration curve results:The methylamine is replaced by 20.0 mL of sodium hydroxide of an identical concentration. If the sodium hydroxide is titrated with the 1.0 M $HCl$, which of the following options accurately describes the pH levels at various points during the titration when compared to the pH levels at the same point in the $HCl$/methylamine titration?
A. lower same higher
B. higher higher same
C. same higher same
D. higher lower lower
|
B Sodium hydroxide is a strong base, which dissociates completely in solution. Thus, it would initially have a higher pH (be more basic) than any weak base of an identical concentration. At equivalence of a strong acid/strong base titration, water is the only acid or base present, causing the solution to have a neutral pH of 7. Finally, in the post-equivalence region of the graph, the pH is driven by the excess $H^+$ from the $HCl$, and that would not change in the new titration.
|
Chemistry/146
|
Chemistry
| null |
The buffer region of this titration is located
A student titrates some 1.0 M $HCl$ into 20.0 mL of methylamine ($CH_3NH_2$), a weak base which only accepts a single proton. The following titration curve results:
A. below 3.0 mL
B. between 3.0 mL and 14.0 mL
C. between 14.0 mL and 16.0 mL
D. above 16.0 mL
|
B A buffer solution is one that resists change in pH due to similar amounts of the base ($CH_3NH_2$) and its conjugate acid ($CH_3NH_3^+$). That occurs after the initial pH change, but prior to the equivalence region. The pH is also stable again starting at 16.5 mL, but that is due to the presence of the excess strong acid, and that does not create a buffer region.
|
Chemistry/147
|
Chemistry
| null |
What is the approximate $pK_b$ for methylamine?
A student titrates some 1.0 M HCl into 20.0 mL of methylamine ($CH_3NH_2$), a weak base which only accepts a single proton. The following titration curve results:
A. 3.5
B. 5.5
C. 10.5
D. 12.5
|
A At the half-equivalence point (7.5 mL) of the titration, $pK_b$ of methylamine = $pOH$ of the solution. To determine the $pOH$, you simply have to see what the $pH$ of the solution is at that half-equivalence point and use $pH + pOH = 14$. The $pH$ at the half-equivalence is 10.5. So, 14 - 10.5 = 3.5.
|
Chemistry/148
|
Chemistry
| null |
What is the concentration of the methylamine?
A student titrates some 1.0 M HCl into 20.0 mL of methylamine ($CH_3NH_2$), a weak base which only accepts a single proton. The following titration curve results:
A. 0.50 M
B. 0.75 M
C. 1.0 M
D. 1.25 M
|
B There is a 1:1 mole ratio between the $HCl$ and the $CH_3NH_2$, meaning there will be the same number of moles of each present at the equivalence point. The equivalence point is located at 15.0 mL of $HCl$ added. (1.0 M)(0.0150 L) = 0.0150 mol $HCl$ = 0.0150 mol $CH_3NH_2$. Finally, divide that value by the volume of the $CH_3NH_2$, 0.0150 mol $CH_3NH_2$ / 0.020 L = 0.75 M $CH_3NH_2$.
|
Chemistry/149
|
Chemistry
| null |
Silver sulfate, $Ag_2SO_4$, has a solubility product constant of $1.0 \times 10^{-5}$. The below diagram shows the products of a precipitation reaction in which some silver sulfate was formed.Which ion concentrations below would have led the precipitate to form?
A. $[Ag^+] = 0.01 M$ $[SO_4^{2-}] = 0.01 M$
B. $[Ag^+] = 0.10 M$ $[SO_4^{2-}] = 0.01 M$
C. $[Ag^+] = 0.01 M$ $[SO_4^{2-}] = 0.10 M$
D. This is impossible to determine without knowing the total volume of the solution.
|
B For a precipitate to form, $Q > K_{sp}$. In this case, $Q = [Ag^+]^2[SO_4^{2-}]$. The concentrations in (B) lead to a $Q$ of $1.0 \times 10^{-4}$, which is greater than the given $K_{sp}$ of $1.0 \times 10^{-5}$. The other options lead to a $Q$ value that is equal to or less than $K_{sp}$.
|
Chemistry/150
|
Chemistry
| null |
Silver sulfate, $Ag_2SO_4$, has a solubility product constant of $1.0 \times 10^{-5}$. The below diagram shows the products of a precipitation reaction in which some silver sulfate was formed.If the beaker above were left uncovered for several hours
A. some of the $Ag_2SO_4$ would dissolve
B. some of the spectator ions would evaporate into the atmosphere
C. the solution would become electrically imbalanced
D. additional $Ag_2SO_4$ would precipitate
|
D Leaving the container uncovered will cause some of the water molecules to evaporate. This allows some $Ag^+$ and $SO_4^{2-}$ ions to "fall" out of solution and combine to create more $Ag_2SO_4$.
|
Chemistry/151
|
Chemistry
| null |
Silver sulfate, $Ag_2SO_4$, has a solubility product constant of $1.0 \times 10^{-5}$. The below diagram shows the products of a precipitation reaction in which some silver sulfate was formed.What is the identity of the excess reactant?
A. $AgNO_3$
B. $Ag_2SO_4$
C. $NaNO_3$
D. $Na_2SO_4$
|
A There are no sulfate ions in solution, which means that whatever the sulfate was attached to was the limiting reactant. Thus, silver must have been attached to the excess reactant, which is $AgNO_3$. (Remember, $Ag_2SO_4$ was the product, not a reactant.)
|
Chemistry/152
|
Chemistry
| null |
The following curve is obtained during the titration of 30.0 mL of 1.0 M $NH_3$, a weak base, with a strong acid:What ions are present in significant amounts during the first buffer region?
A. $NH_3$ and $NH_4^+$
B. $NH_3$ and $H^+$
C. $NH_4^+$ and $OH^-$
D. $H_3O^+$ and $NH_3$
|
A The reaction occurring is $NH_3 + H^+ \rightleftharpoons NH_4^+$. During the first buffer region, all added hydrogen ions immediately react with $NH_3$ to create $NH_4^+$. $NH_3$ remains in excess until equilibrium is achieved.
|
Chemistry/153
|
Chemistry
| null |
The following curve is obtained during the titration of 30.0 mL of 1.0 M NH3, a weak base, with a strong acid:What is the concentration of the acid?
A. 0.5 M
B. 1.0 M
C. 1.5 M
D. 2.0 M
|
D At the equivalence point, the moles of acid are equal to the moles of base. Moles base = $(1.0 M)(0.030 L) = 0.030$ mol base = 0.030 moles acid It requires 15.0 mL of acid to reach equivalence, so: https://img.apstudy.net/ap/chemistry/cr20/0307_Image_0004.jpg
|
Chemistry/154
|
Chemistry
| null |
Why is the solution acidic at equilibrium?
The following curve is obtained during the titration of 30.0 mL of 1.0 M NH3, a weak base, with a strong acid:
A. The strong acid dissociates fully, leaving excess $[H^+]$ in solution.
B. The conjugate acid of NH3 is the only ion present at equilibrium.
C. The water which is being created during the titration acts as an acid.
D. The acid is diprotic, donating two protons for every unit dissociated.
|
B The reaction here is $NH_3 + H^+ \rightleftharpoons NH_4^+$. At equilibrium, the moles of $NH_3$ and $H^+$ would be equal, leaving behind $NH_4^+$ ions, which will then donate ions to water, creating an acidic medium.
|
Chemistry/155
|
Chemistry
| null |
The diagram below shows three identical 1.0 L containers filled with the indicated amounts of gas. The stopcocks connecting the containers are originally closed and the gases are all at 25°C. Assume ideal behavior.The stopcocks are opened. If the tubing connecting the containers has negligible volume, by what percentage will the pressure exerted by the neon gas decrease?
A. 25%
B. 33%
C. 50%
D. 67%
|
D $P_1V_1 = P_2V_2$ $P_1(1.0 L) = P_2(3.0 L)$ $P_2/P_1 = 1.0/3.0$ Thus, the pressure of the neon gas is 33% of what it was originally, meaning a decrease of 67%. Note that the same calculation could be used for any of the gases; each gas is expanding to take up three times as much space as it has originally, and thus exerts one-third as much pressure.
|
Chemistry/156
|
Chemistry
| null |
The diagram below shows three identical 1.0 L containers filled with the indicated amounts of gas. The stopcocks connecting the containers are originally closed and the gases are all at 25°C. Assume ideal behavior.Which gas has the strongest IMFs?
A. He
B. Ne
C. NO
D. All gases have identical IMFs.
|
D One of the precepts of kinetic molecular theory is that gas molecules exert no forces on each other; thus, in all containers there are no IMFs present.
|
Chemistry/157
|
Chemistry
| null |
The diagram below shows three identical 1.0 L containers filled with the indicated amounts of gas. The stopcocks connecting the containers are originally closed and the gases are all at 25°C. Assume ideal behavior. Which gas exerts the greatest pressure?
A. He
B. Ne
C. NO
D. All gases exert the same amount of pressure.
|
A Pressure is directly dependent on the number of moles. In their respective containers, there are 5 moles of He, 2 moles of Ne, and 1 mole of NO. As there are the most moles of He, the He must exert the greatest pressure.
|
Chemistry/158
|
Chemistry
| null |
Which structure is more likely to correspond with the actual Lewis diagram for the sulfate ion?
There are several different potential Lewis diagrams for the sulfate ion, two of which are below.
A. Structure A; single bonds are more stable than double bonds
B. Structure A; it has the most unshared pairs of electrons
C. Structure B; there are more possible resonance structures
D. Structure B; fewer atoms have formal charges
|
D The formal charge tables for each diagram are below (note: for structure B, the double-bonded oxygens are the first two, and the single bonded are the last two).  The total formal charge on each potential structure is -2, which is correct, as that is the charge on a sulfate ion. However, the right-hand structure has fewer atoms with formal charges, making it the more likely structure.
|
Chemistry/159
|
Chemistry
| null |
Which of the following statements regarding the structure B is true?
There are several different potential Lewis diagrams for the sulfate ion, two of which are below.
A. The double bonds must be located opposite of each other due to additional electron repulsion.
B. It is a more polar molecule than the molecule represented by structure A.
C. The bonds in the molecule are weaker than those in structure A.
D. All bonds in the molecule are identical to each other.
|
D In any molecule displaying resonance, all bonds are identical.
|
Chemistry/160
|
Chemistry
| null |
What is the S-O bond order in the structure B?
There are several different potential Lewis diagrams for the sulfate ion, two of which are below.
A. 1.0
B. 1.33
C. 1.5
D. 1.67
|
C Six total bonds divided by four locations gives a bond order of 1.5.
|
Chemistry/161
|
Chemistry
| null |
What is the molecular geometry in the structure A?
There are several different potential Lewis diagrams for the sulfate ion, two of which are below.
A. Tetrahedral
B. Trigonal Planar
C. Trigonal Pyramidal
D. Octahedral
|
A Four charge clouds and no lone pairs means tetrahedral geometry.
|
Chemistry/162
|
Chemistry
| null |
Use the PES spectra below to answer questions.How many valence electrons does this atom have?
A. 2
B. 3
C. 4
D. 5
|
D Valence electrons are those in the outermost energy level. In this case, that is the third level, which has five valence electrons in it (two in 3s and three in 3p).
|
Chemistry/163
|
Chemistry
| null |
An electron from which peak would have the greatest velocity after ejection?
Use the PES spectra below to answer questions.
A. The peak at 104 MJ/mol
B. The peak at 6.84 MJ/mol
C. The peak at 4.98 MJ/mol
D. The peak at 1.76 MJ/mol
|
D The less ionization energy that is required to remove an electron, the more kinetic energy that electron will have after ejection.
|
Chemistry/164
|
Chemistry
| null |
How many significant digits are present in the temperature read from the thermometer illustrated to the right?
A.1
B.2
C.3
D.4
|
C The number is 27.5, which have 3 significant digits.
|
Chemistry_extra/1
|
Chemistry
| null |
The marks on the following target represent someone who is:
A.accurate, but not precise.
B.precise, but not accurate.
C.both accurate and precise.
D.neither accurate nor precise.
|
D They are not centered on the bulls eye and not close to each other
|
Chemistry_extra/2
|
Chemistry
| null |
Pictured below is a schematic of the Rutherford experiment. Which scattered -particle gives the best evidence for the nuclear atom?
A. a
B. b
C. c
D. d
|
A
|
Chemistry_extra/3
|
Chemistry
| null |
What position on the standing wave shown below corresponds to a crest?
A. a
B. b
C. c
D. d
E. e
|
B
|
Chemistry_extra/4
|
Chemistry
| null |
The value of l that is related to the following orbital is:
A. 0
B. 1
C. 2
D. 3
E. 4
|
B This is a p-orbital, whose value l should be 1.
|
Chemistry_extra/5
|
Chemistry
| null |
The titration curves labeled 1 and 2 were obtained by titrating equal volumes of two different acid samples with portions of the same sodium hydroxide solution. What conclusions can be drawn about the relative concentrations and strengths of acids 1 and 2 from these curves?
(A) The concentrations are the same but acid 1 is weaker than acid 2.
(B) The concentrations are the same but acid 1 is stronger than acid 2.
(C) Acid 1 is the same strength as acid 2, but it is less concentrated.
(D) Acid 1 is the same strength as acid 2, but it is more concentrated.
|
A The concentrations are the same because they take the same amount.
|
Chemistry_extra/6
|
Chemistry
| null |
According to the above data, what is the half-life of the substance?
A. 1.0 hrs
B. 2.3 hrs
C. 3.0 hrs
D. 8.0 hrs
|
C
|
Chemistry_extra/7
|
Chemistry
| null |
What percent of the original sample remains after 4 hours?
A. 80%
B. 75%
C. 60%
D. 40%
|
D
|
Chemistry_extra/7
|
Chemistry
| null |
The elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer which separates a sample by mass into isotopes, resulting in the data below. All of the following statements are true. Which one would be the best basis for concluding that the sample was pure Te?
A. Te forms ions with a -2 charge, whereas I forms ions with a -1 charge.
B. Te is more abundant than I in the universe.
C. I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope
D. I has a higher first ionization energy than Te does.
|
C The graph shows different isotopes by mass. Remember that isotopes of an element have a different number of neutrons, giving them a different mass number. If
Iodine only has one isotope with 74 neutrons, it’s mass should be 127 (74 neutrons + 53 protons). There is no peak at 127, so the mixture must not have any iodine.
|
Chemistry_extra/8
|
Chemistry
| null |
The diagram below models a change that occurs in matter. Based on what you know about changes in matter, explain why the diagram shows a physical change rather than a chemical change.
A. The particles get smaller.
B. The volume of the matter decreases.
C. The composition of the matter stays the same.
D. The particles change into particles of different substances
|
C In physical changes, the bonds/particles do not change. In this diagram they did not change, they just condensed. This represents gas becoming liquid or solid.
|
Chemistry_extra/9
|
Chemistry
| null |
In an experiment, a solid 1 molar sample of Substance A was gradually heated by a source of constant energy for several hours and the temperature was measured periodically. At the end of the heating period, Substance A had been converted to the gas phase. The heating curve produced by this experiment is shown below. During the course of the experiment, there was a period of time when the phase of Substance A was in equilibrium with the liquid phase. At what temperature did this occur?
(A) Between 100 K and 150 K
(B) At 150 K
(C) Between 150 K and 250 K
(D) At 250 K
(E) Between 250 K and 350 K
|
B The first flat part of the heating curve corresponds to the phase change from solid to liquid. During the phase change, an equilibrium exists between the two phases.
|
Chemistry_extra/10
|
Chemistry
| null |
In an experiment, a solid 1 molar sample of Substance A was gradually heated by a source of constant energy for several hours and the temperature was measured periodically. At the end of the heating period, Substance A had been converted to the gas phase. The heating curve produced by this experiment is shown below. Based on the data given in the heating curve,which of the following statements is NOTtrue regarding Substance A?
(A) The boiling point of Substance A is 250 K.
(B) The freezing point of Substance A is150 K.
(C) The heat of vaporization of Substance A is greater than the heat of fusion.
(D) Substance A is a liquid at room temperature.
(E) The intermolecular forces exhibited by Substan
|
D Choice (D) is the only choice that's not true. Room temperature is about 298 K. At 298 K,Substance A is in the gas phase, not the liquid phase. As for the other answers, Choices (A)and (B) accurately give the boiling and freezing points. Choice (C) is accurate because the vaporization line is much longer than the fusion line. Heat of vaporization is usually much higher than heat of fusion. Choice (E) is accurate because the boiling and freezing points of substance A are lower than those of water, so Substance A must be held together by weaker intermolecular forces.
|
Chemistry_extra/10
|
Chemistry
| null |
In an experiment, a solid 1 molar sample of Substance A was gradually heated by a source of constant energy for several hours and the temperature was measured periodically. At the end of the heating period, Substance A had been converted to the gas phase. The heating curve produced by this experiment is shown below. During the course of the experiment,Substance A was gradually heated from 100K to 350 K. When the temperature reached 250 K, the energy absorbed by Substance A?
(A} was used to change from liquid to gas phase.
(B) was used to change from gas to liquid phase.
(C) was used to change from solid to liquid phase.
(D) was used to change from liquid to solid phase.
(E) was reduced to zero.
|
A At 250 K, Substance A boiled. That means that the temperature remained constant while the energy absorbed was used to break up the forces holding the liquid together and convert the substance to a gas.
|
Chemistry_extra/10
|
Chemistry
| null |
Which of the following is true of the reactions shown in the diagram above?
(A) The reaction is endothermic because the reactants are at a higher energy level than the products.
(B) The reaction is endothermic because the reactants are at a lower energy level than the products.
(C) The reaction is exothermic because the reactants are at a higher energy level than the products.
(D) The reaction is exothermic because the reactants are at a lower energy level than the products.
(E) The reaction is endothermic because the reactants are at the same energy level as the products.
|
C In an exothermic reaction, energy is given off as the products are created because the products have less potential energy than the reactants.
|
Chemistry_extra/11
|
Chemistry
| null |
Which point on the graph shown above corresponds to an activated complex or transition state?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5
|
C Point 3 represents the activated complex, which is the ppint of highest energy. This point is the transition state between the reactants and the products.
|
Chemistry_extra/12
|
Chemistry
| null |
The following titration curve shows the titration of a weak base with a strong acid. Which of the following values most accurately approximates the p$K_b$ of the weak base?
(A) 9.8
(B) 8.4
(C) 7
(D) 3.3
(E) 4.2
|
E The half equivalence point of this titration, is around pH= 9.8. At the half equivalence point, the amount of
base (which we can call [A-] as we do when talking about acids and pH values) is equal to the neutralized base [HA]. When these two quantities are equal, the H-H equation tells us that the
pH = the $pK_a$, which when subtracted from 14 gives the $pK_b$. Therefore, the answer = 4.2.
|
Chemistry_extra/13
|
Chemistry
| null |
Given a reaction A+B →C. Based on the following experimental data, what is the rate law for the hypothetical reaction given above?
(A) Rate= $k[A]$
(B) Rate= $k[A]^2$
(C) Rate = $k[B]$
(D) Rate = $k[B]^2$
(E) Rate = $k[A][B]$
|
C From a comparison of experiments 1 and 2, when [B] is doubled while [A] is held constant, the rate doubles. That means that the reaction is first order with respect to B.From a comparison of experiments 2 and 3, when [A] is doubled while [B] is held constant, the rate doesn't change. That means that the reaction is zero order with respect to A and that A will not appear in the rate law.So the rate law is Rate= k[B].
|
Chemistry_extra/14
|
Chemistry
| null |
Given a reaction A+B →C. Based on the following experimental data, what is the rate law for the hypothetical reaction given above?
(A) Rate= $k[A]$
(B) Rate= $k[A]^2$
(C) Rate = $k[B]$
(D) Rate = $k[B]^2$
(E) Rate = $k[A][B]$
|
E From a comparison of experiments 1 and 2, when [B] is doubled while [A] is held constant, the rate doubles. That means that the reaction is first order with respect to B.From a comparison of experiments 2 and 3, when both [A] and [B] are doubled, the rate increases by a factor of 4. We would expect the rate to double based on the change in B; because the rate is in fact multiplied by 4, the doubling of A must also change the rate by a factor of 2, so the action is also first order with respect to A.So the rate law is Rate= k[A][B].
|
Chemistry_extra/15
|
Chemistry
| null |
Given a reaction A+B →C. Based on the following experimental data, what is the rate law for the hypothetical reaction given above?
(A) Rate= $k[A][B]$
(B) Rate= $k[A]^2$
(C) Rate = $k[A][B]^2$
(D) Rate = $k[B]^2$
(E) Rate = $k[A]^2[B]^2$
|
C From a comparison of experiments 1 and 2, when [A] is quadrupled while [B] is held constant, the rate quadruples. That means that the reaction is first order with respect to A. From a comparison of experiments 2 and 3, when [B] is doubled while [A] is held constant, the rate quadruples. That means that the reaction is second order with respect to B.So the rate law is Rate = k[A][B]^2.
|
Chemistry_extra/16
|
Chemistry
| null |
The formal charge on carbon in the molecule below is.
A) 0
B) +1
C) -1
D) +3
E) +2
|
A
|
Chemistry/165
|
Chemistry
| null |
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