Exam 2

Consider the reaction N2(g) + O2(g) 2NO(g), for which Kc = 0.10 at 2000ºC. Starting with initial concentrations of 0.040 M for N2 and 0.040 M for O2, what is the equilibrium concentration of NO? 0.10 M 0.011 M 0.080 M 0.019 M 0.0096 M

0.011 M

Calculate KP for the reaction 2NOCl(g) <=> 2NO(g) + Cl2(g) at 400.°C if Kc at 400.°C for this reaction is 2.1 × 10-2. (R = 0.08206 L • atm/K • mol) 1.2 0.69 1.7 × 10-3 6.4 × 10-3 3.8 × 10-4

1.2

A 25.0-mL sample of 1.00 M NH3 is titrated with 0.15 M HCl. What is the pH of the solution after 15.00 mL of acid have been added to the ammonia solution? [Kb(NH3) = 1.8 × 10-5] 10.26 9.21 8.30 9.30 8.21

10.26

What is the pOH of a 0.025 M HI solution? 1.60 12.40 0.94 0.025 10.31

12.40

What is the pH of a 0.050 M LiOH solution? 3.00 11.00 1.30 12.70 12.39

12.70

Which pair of substances could form a buffered aqueous solution? H3PO4, NaH2PO4 HCl, NaCl NH3, NaOH H2SO4, CH3COOH HNO3, NaNO3

H3PO4, NaH2PO4

Which is the strongest acid? HBrO3 HFO3 HClO3 HIO3 All are of equal strength.

HFO3 WRONG

Which is the best acid to prepare a buffer with the lowest pH? HOC6H4OCOOH, Ka = 1.0 × 10-3 HBrO, Ka = 2.3 × 10-9 C6H4(COOH)2, Ka = 2.9 × 10-4 CH3COOH, Ka = 1.8 × 10-5 C5H5O5COOH, Ka = 4.0 × 10-6

HOC6H4OCOOH, Ka = 1.0 × 10-3

Which is included in the Ksp expression? I. Concentration of cation II. Concentration of anion III. Concentration of solid I only II only III only I and II I, II and III

I and II

The reaction 2H2O2(g) 2H2O(g) + O2(g) is exothermic, ΔHºrxn = -210 kJ/mol. Which one of the following is correct? KP depends only on the pressure. Temperature does not affect KP KP depends on total pressure as well as temperature. KP at 800 K is smaller than KP at 1200 K. KP at 1200 K is smaller than KP at 800 K.

KP at 1200 K is smaller than KP at 800 K

Which of the following is correct? Solubility is the concentration of unsaturated ions in solution. Ksp is the solubility product constant for a precipitate. Solubility = Kw × Ksp. Ksp is the same as the solubility. Ksp is an equilibrium constant and solubility is the concentration of a saturated solution.

Ksp is an equilibrium constant and solubility is the concentration of a saturated solution.

What is the conjugate base of NH3? NH2+ NH4+ NH2- NH4 NH2

NH4+ WRONG

For PbCl2 (Ksp = 2.4 × 10-4), will a precipitate of PbCl2 form when 0.10 L of 3.0 × 10-2 M Pb(NO3)2 is added to 400 mL of 9.0 × 10-2 M NaCl? No, because Q = Ksp. Yes, because Q > Ksp. No, because Q < Ksp. Yes, because Q < Ksp.

Yes, because Q < Ksp. WRONG

Hydrogen iodide decomposes according to the equation 2HI(g) <=> H2(g) + I2(g), for which Kc = 0.0156 at 400ºC. Suppose 0.550 mol HI was injected into a 2.00-L reaction vessel at 400ºC. What is the concentration of H2 at equilibrium? 0.0275 M 0.0550 M 0.138 M 0.220 M 0.275 M

.0275 M

At a certain temperature the reaction CO2(g) + H2(g) <=> CO(g) + H2O(g) has Kc = 2.50. If 2.00 mol of carbon dioxide and 1.50 mol of hydrogen are placed in a 5.00-L vessel and equilibrium is established, what is the equilibrium concentration of carbon monoxide? 1.33 M 0.209 M 0.600 M 0.667 M 0.267 M

0.209 M

At elevated temperatures, hydrogen iodide may decompose to form hydrogen gas and iodine gas, as follows. 2HI(g) H2(g) + I2(g) In a particular experiment, the concentrations at equilibrium were measured to be [HI] = 0.85 mol/L, [I2] = 0.60 mol/L, and [H2] = 0.27 mol/L. What is Kc for the above reaction? 0.19 1.6 × 102 4.5 5.3 0.22

0.22

The pH of a Ba(OH)2 solution is 10.00. What is the H+ ion concentration of this solution? 10.00 M 4.0 × 10-11 M 1.3 × 10-5 M 1.6 × 10-10 M 1.0 × 10-10 M

1.0 × 10-10 M

When the reaction 2H2S(g) <=> 2H2(g) + S2(g) is carried out at 1065°C, KP = 0.012. Starting with pure H2S at 1065°C, what must the initial pressure of H2S be if the equilibrated mixture at this temperature is to contain 0.250 atm of H2(g)? 1.86 atm 1.06 atm 0.94 atm 1.52 atm 0.90 atm

1.06 atm

Find the pH of a 0.20 M aqueous solution of dichloroacetic acid, for which Ka = 3.32 × 10-2. 1.05 1.18 0.75 2.71 2.35

1.18

Find the pH of a 0.135 M aqueous solution of periodic acid (HIO4), for which Ka = 2.3 × 10-2. 3.28 1.34 1.64 1.25 1.17

1.34

A 0.15 M solution of chloroacetic acid has a pH of 1.86. What is the value of Ka for this acid? 1.4 × 10-3 7.2 × 101 1.6 × 10-1 9.9 × 10-2 2.7 × 10-4

1.4 × 10-3

The equilibrium constant, KP, has a value of 6.5 × 10-4 at 308 K for the reaction of nitrogen monoxide with chlorine. 2NO(g) + Cl2(g) <=> 2NOCl(g) What is the value of Kc? (R = 0.08206 L • atm/K • mol) 1.6 × 10-2 6.5 × 10-4 1.7 2.5 × 10-7 None of these choices is correct.

1.6 × 10-2

What is the value of Kb for the cyanide anion, CN-? Ka(HCN) = 6.2 × 10-10 1.6 × 10-5 1.6 × 10-4 6.2 × 104 3.8 × 10-5 3.8 × 10-4

1.6 × 10-5

The molar solubility of manganese(II) carbonate is 4.2 × 10-6 M. What is Ksp for this compound? 2.0 × 10-3 3.0 × 10-16 1.8 × 10-11 4.2 × 10-6 8.4 × 10-6

1.8 × 10-11

What is the pH of a 0.050 M triethylamine, (C2H5)3N, solution? Kb for triethylamine is 5.3 × 10-4. 8.68 2.31 5.32 11.69 1.30

11.69

Suppose 50.0 g of N2O4 is introduced into an evacuated 2.00-L vessel and allowed to come to equilibrium with its decomposition product, N2O4(g) 2NO2(g). For this reaction Kc = 0.133. Once the system has reached equilibrium, 5.00 g of NO2 is injected into the vessel, and the system is allowed to equilibrate once again. What is the mass of NO2 in the final equilibrium mixture? 12.4 g 15.5 g 14.7 g 7.8 g 19.7 g

15.5 g

The equilibrium constant for the reaction Ni(s) + 4CO(g) Ni(CO)4(g) is 5.0 × 104 at 25ºC. What is the equilibrium constant for the following reaction? Ni(CO)4(g) Ni(s) + 4CO(g)? 2.0 × 10-5 2.0 × 10-3 5.0 × 104 5.0 × 10-4 2.5 × 109

2.0 × 10-5

At 340. K, KP = 69 for the reaction H2(g) + I2(g) <=> 2HI(g). Suppose 50.0 g of HI is injected into an evacuated 5.00-L rigid cylinder at 340. K. What is the total pressure inside the cylinder when the system comes to equilibrium? 0.171 atm 2.18 atm 1.76 atm 0.424 atm 2.60 atm

2.18 atm ??

What is the H+ ion concentration in a 2.1 × 10-4 M Ca(OH)2 solution? 4.8 × 10-11 M 4.2 × 10-4 M 2.4 × 10-11 M 2.1 × 10-4 M 7.3 × 10-4 M

2.4 × 10-11 M

For the nitrogen fixation reaction, 3H2(g) + N2(g) 2NH3(g), Kc = 6.0 × 10-2 at 500°C. If 0.250 M H2 and 0.050 M NH3 are present at equilibrium, what is the equilibrium concentration of N2? 0.058 M 0.083 M 2.7 M 0.20 M 3.3 M

2.7 M

Calculate the NaOH concentration necessary to precipitate Ca(OH)2 from a solution in which [Ca2+] = 1.0. Ksp of Ca(OH)2 = 8 × 10-6. 0.10 M 6.7 × 10-8 M 1.5 × 10-7 M 2.8 × 10-3 M

2.8 × 10-3 M

At 1500°C the equilibrium constant for the reaction CO(g) + 2H2(g) CH3OH(g) has the value KP = 1.4 × 10-7. What is ΔG° for this reaction at 1500°C? (R = 8.314 J/K • mol) -105 kJ/mol 1.07 kJ/mol 105 kJ/mol -233 kJ/mol 233 kJ/mol

233 kJ/mol

In which of these gas-phase equilibria is the yield of products increased by increasing the total pressure on the reaction mixture? 2NO(g) + Cl2(g) <=> 2NOCl(g) 2SO3(g) <=> 2SO2(g) + O2(g) PCl5(g) <=> PCl3(g) + Cl2(g) 2H2O2 (g) <=> 2H2O(g) + O2(g) CO(g) + H2O(g) <=> CO2(g) + H2(g)

2NO(g) + Cl2(g) <=> 2NOCl(g)

Compounds A, B, and C react according to the following equation. 3A(g) + 2B(g) 2C(g) At 100°C a mixture of these gases at equilibrium showed that [A] = 0.855 M, [B] = 1.23 M, and [C] = 1.75 M. What is the value of Kc for this reaction? 3.24 2.25 0.309 0.601 1.66

3.24

A 50.00-mL solution of 0.10 M HNO2 is titrated with a 0.10 M KOH solution. After 25.00 mL of the KOH solution is added, what is the pH in the titration flask? [Ka(HNO2) = 4.5 × 10-4] 2.17 7.00 2.41 1.48 3.35

3.35

For the reaction 2NOCl(g) 2NO(g) + Cl2(g), Kc = 8.0 at a certain temperature. What concentration of NOCl must be put into an empty 4.00 - reaction vessel in order that the equilibrium concentration of NOCl is 1.00 M? 11.0 M 1.26 M 2.25 M 3.52 M 2.50 M

3.52 M

Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C6H5CO2H) and 0.15 M sodium benzoate (C6H5COONa). (Ka = 6.5 × 10-5 for benzoic acid) 4.83 3.97 4.41 3.40 4.19

3.97

What is [OH-] for a solution at 25°C that has [H3O+] = 2.35 × 10-3 M? 2.35 × 10-11 M 4.26 × 10-5 M 2.35 × 10-3 M 4.26 × 10-12 M 2.35 × 10-17 M

4.26 × 10-12 M

What is the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter of solution? [Ka(HCNO) = 2.0 × 10-4] 4.30 4.40 3.70 3.10 0.97

4.30

What is the pH of a solution that consists of 0.50 M H2C6H6O6 (ascorbic acid) and 0.75 M NaHC6H6O6 (sodium ascorbate)? [Ka(H2C6H6O6) = 6.8 × 10-5] 3.76 4.34 4.57 3.99 5.66

4.34

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of sodium cyanate (NaCNO) and 1.0 mole of cyanic acid (HCNO) in enough water to make 1.0 liter of solution. [Ka(HCNO) = 2.0 × 10-4] 0.00 5.00 3.70 3.00 4.40

4.40 WRONG

The indicator propyl red has Ka = 3.3 × 10-6. What would be the approximate pH range over which it would change color? 4.5 - 6.5 7.5 - 9.5 5.5 - 7.5 6.5 - 8.5 3.5 - 5.5

4.5 - 6.5

A buffer is prepared by adding 300.0 mL of 2.0 M NaOH to 500.0 mL of 2.0 M CH3COOH. What is the pH of this buffer? [Ka(CH3COOH) = 1.8 × 10-5] 4.57 4.87 4.92 4.52 4.97

4.92

Calculate the pH at the equivalence point for the titration of 50.0 mL of 0.20 M NH3 with 0.20 M HCl. [Kb(NH3) = 1.8 × 10-5] 7.00 5.13 11.13 4.98 2.87

5.13

What is the concentration of Pb2+ ions in a solution prepared by adding 5.00 g of lead(II) iodide to 500. mL of 0.150 M KI? [Ksp(PbI2) =1.4 × 10-8] 2.2 × 10-2 M 1.4 × 10-8 M 6.2 × 10-7 M 9.3 × 10-8 M 1.5 × 10-7 M

6.2 × 10-7 M

Calculate the minimum concentration of Mg2+ that must be added to 0.10 M NaF in order to initiate a precipitate of magnesium fluoride. [Ksp(MgF2) = 6.9 × 10-9] 6.9 × 10-9 M 1.7 × 10-7 M 6.9 × 10-7 M 1.4 × 107 M 6.9 × 10-8 M

6.9 × 10-7 M

Which of the following is an exact or approximate value of the pH at the equivalence point of a titration of a strong acid with a strong base? 1.0 0.0 7.0 3.5 14.0

7.0 WRONG

Hydrogen peroxide (H2O2) decomposes according to the following equation. H2O2(l) → H2O(l) + 1/2 O2(g). What is KP for this reaction at 25°C? (ΔH° = -98.2 kJ/mol, ΔS° = 70.1 J/K • mol, R = 8.314 J/K • mol) 3.46 × 1017 1.3 × 10-21 8.6 × 104 20.9 7.4 × 1020

7.4 × 1020

Suppose 75.0 g of PCl5(g) is introduced into an evacuated 3.00-L vessel and allowed to reach equilibrium at 250ºC. PCl5(g) PCl3(g) + Cl2(g) If KP = 1.80 for this reaction, what is the total pressure inside the vessel at equilibrium? (R = 0.0821 atm • L/mol • K) 4.54 atm 7.43 atm 9.69 atm 2.28 atm 2.88 atm

7.43 atm

What is the pH of a buffer that consists of 0.20 M NaH2PO4 and 0.40 M Na2HPO4? [Ka(NaH2PO4) = 6.2 × 10-8] 7.51 8.13 7.90 6.51 6.91

7.51

At what temperature is KP = 4.00 for the reaction N2O4(g) 2NO2(g)? Substance ΔH°f (kJ/mol) S° (J/K • mol) NO2(g) 33.85 240.46 N2O4(g) 9.66 304.3 (R = 8.314 J/K • mol) 56°C 476°C 197°C 36°C 79°C

79°C

What is the [H3O+] in a solution that consists of 1.5 M NH3 and 2.5 M NH4Cl? Kb = 1.8 × 10-5 5.6 × 10-10 M 1.1 × 10-5 M 3.0 × 10-6 M 9.3 × 10-10 M 3.3 × 10-9 M

9.3 × 10-10 M

Which best describes the pH at the equivalence point of a titration of a weak base with a strong acid? Close to 7.0 Between 0 and 7 Greater than 14 Between 7 and 14 Less than zero

Between 7 and 14

Which is the strongest base? NH3, Kb = 1.8 × 10-5 C2H5NH2, Kb = 5.6 × 10-4 CH3NH2, Kb = 4.4 × 10-4 H2NCONH2, Kb = 1.5 × 10-14 C5H5N, Kb = 1.7 × 10-9

C2H5NH2, Kb = 5.6 × 10-4

Which is the best choice for preparing a buffer with a pH of 3.5? CH3COOH, Ka = 1.8 × 10-5 HOC6H4OCOOH, Ka = 1.0 × 10-3 C6H4(COOH)2, Ka = 2.9 × 10-4 HBrO, Ka = 2.3 × 10-9 C5H5O5COOH, Ka = 4.0 × 10-6

C5H5O5COOH, Ka = 4.0 × 10-6 WRONG

Acid strength increases in the series HCN < HF < HSO4-. Which of these species is the strongest base? SO42- H2SO4 CN - HSO4- F-

CN-

For the following reaction at equilibrium, which one of the changes below would cause the equilibrium to shift to the left? 2NOBr(g) 2NO(g) + Br2(g), ΔHºrxn = 30 kJ/mol Decrease the temperature Remove some NO Remove some Br2 Increase the container volume Add more NOBr

Decrease the temperature

What is defined as a fraction with product concentrations in the numerator and reactant concentrations in the denominator and with each concentration raised to a power equal to the corresponding stoichiometric coefficient in the balanced chemical equation? Reaction expression Reversibility expression Mass action Reaction quotient Equilibrium expression

Equilibrium expression WRONG

For the following reaction at equilibrium in a reaction vessel, which one of these changes would cause the I2 concentration to increase? 2NOI(g) <=> 2NO(g) + I2(g), ΔHºrxn = 45.3 kJ/mol Decrease the temperature Remove some NOI Increase the system pressure Add some NO Expand the gas mixture into a larger volume

Expand the gas mixture into a larger volume ???

Which is the weakest acid? HBrO HBrO4 HBr HBrO2 HBrO

HBrO

What is the conjugate acid of the acetate ion? CH3O2- COOH H2O CH4 HC2H3O2

HC2H3O2

A container was charged with hydrogen, nitrogen, and ammonia gases at 120°C and the system was allowed to reach equilibrium. What will happen if the volume of the container is increased at constant temperature? 3H2(g) + N2(g) <=> 2NH3(g) There will be no effect. The equilibrium constant will increase. The equilibrium constant will decrease. Hydrogen and nitrogen will be produced at the expense of ammonia. More ammonia will be produced at the expense of hydrogen and nitrogen.

Hydrogen and nitrogen will be produced at the expense of ammonia.

A 50.0-mL sample of a 0.100 M solution of a weak acid HA has an equilibrium pH of 4.00. After 1.0 × 10-3mol of a substance X is added to the solution, it is observed that the pH of the solution increases. What might be true about substance X? I. X might be a strong base that partially neutralized some weak acid. II. X might be a strong acid that made the solution more acidic. III. X might be a soluble ionic compound containing the anion A-. I only II only III only I or III II or III

III only WRONG

What is the name for Qc? Reaction expression Mass action Equilibrium expression Reaction quotient Reversibility expression

Reaction quotient

For the following reaction at equilibrium, which choice gives a change that will shift the position of equilibrium to favor formation of more products? 2NOBr(g) <=> 2NO(g) + Br2(g), ΔHºrxn = 30 kJ/mol Remove Br2 Remove NOBr selectively Increase the total pressure by decreasing the volume Lower the temperature Add more NO

Remove Br2

Which is the weakest acid? HSO3- SO42- H2SO3 H2SO4 HSO4-

SO42- WRONG

After 50.0 mL of a 0.100 M solution of NaOH is added to 50.0 mL of a 0.100 M solution of an unknown acid, the equilibrium pH is basic. What may be concluded about the identity of the acid? The acid can only be a strong monoprotic acid. The acid could be either a strong or weak acid, and could be either a monoprotic, diprotic, orpolyprotic acid. The acid must be a strong acid, but could be either monoprotic, diprotic, or polyprotic. The acid must be a weak acid, but could be either monoprotic, diprotic, or polyprotic. The acid can only be a weak monoprotic acid.

The acid can only be a weak monoprotic acid ???

Which of the following is correct for the equivalence point in an acid-base titration? The pH is equal to the pKa of the weak acid. The amounts of acid and base combined are in a stoichiometric ratio at the equivalence point in an acid-base titration. The pH is 7.0. The pH is at its highest value for any reaction. The pH is equal to the pKb of the weak base.

The pH is 7.0. WRONG

The acid dissociation constant Ka equals 1.26 × 10-2 for HSO4- and is 5.6 × 10-10 for NH4+. Which statement about the following equilibrium is correct? HSO4-(aq) + NH3(aq) SO42-(aq) + NH4+(aq) The products will be favored because the hydrogen sulfate ion is a stronger acid than the ammonium ion. Neither reactants nor products will be favored because all of the species are weak acids or bases. This reaction is impossible to predict, since the strong acid and the weak base appear on the same side of the equation. The initial concentrations of the hydrogen sulfate ion and ammonia must be known before any prediction can be made. The reactants will be favored because ammonia is a stronger base than the sulfate anion.

The products will be favored because the hydrogen sulfate ion is a stronger acid than the ammonium ion.

Ammonium chloride is used as an electrolyte in dry cells. Which statement about a 0.10 M solution of NH4Cl is correct? The solution is strongly basic. The solution is acidic. The solution is weakly basic. The solution is neutral. The values for Ka and Kb for the species in solution must be known before a prediction can be made.

The solution is acidic.

A solution is prepared by adding 0.10 mol of potassium chloride, KCl, to 1.00 L of water. Which statement about the solution is correct? The solution is basic. The solution is neutral. The solution is a strong oxidant. The solution is acidic. The values for Ka and Kb for the species in solution must be known before a prediction can be made.

The solution is neutral.

Suppose 0.015 mol of KOH is added to 1.00 L of 0.0010 M Ca(NO3)2. Which statement is correct? [Ksp(Ca(OH)2) = 6.5 × 10-6] Potassium nitrate precipitates until the solution is saturated. The concentration of calcium ions is reduced by the addition of the hydroxide ions. The presence of KOH will raise the solubility of Ca(NO3)2. The solution is unsaturated and no precipitate forms. Calcium hydroxide precipitates until the solution is saturated.

The solution is unsaturated and no precipitate forms.

When a strong acid is titrated with a strong base, the pH at the equivalence point is equal to 7.0. is equal to 3.5. is equal to the pKa of the acid. is greater than 7.0. is between 3.5 and 7.0.

is greater than 7.0. WRONG

When the concentration of the conjugate base of a weak acid is less than the concentration of the weak acid in a buffer solution, the pH of the solution is equal to the pKa. less than the pKa. greater than the pKa. always basic. always acidic.

less than the pKa.

Which of the following statements is incorrect regarding equilibrium? Physical equilibrium cannot exist between phases. Chemical equilibrium is a reversible process with no net change in concentrations of the products and reactants. A chemical equilibrium with all reactants and products in the same phase is homogeneous. none of the above

none of the above WRONG

Which aqueous solution has the highest pH? 0.1 M CH3COOH, pKa = 4.7 0.1 M ZnCl2, pKa = 9.0 pure water 0.1 M H3C6H5O7, pKa = 3.1 0.1 M CuCl2, pKa = 7.5

pure water WRONG