CHEM Exam 3

The normal freezing point of sulfur dioxide is -72 ºC. For the process, SO2(l) → SO2(s) at -80 ºC, the signs of ΔH, ΔS, and ΔG would be: ΔH ΔS ΔG (separate answers with commas, no space ex. 1,2,3

-,-,-

Using the values below, calculate ΔG ºrxn for the reaction below at 25 ºC. Hg2+(aq) + 2Cl^-(aq) → HgCl2(s) ΔHºf (kJ/mol) Sº (J/K*mol) Hg^2+(aq) +171.1 -32.2 Cl^-(aq) -167.2 56.5 HgCl2(s) -224.0 146

-80.1 kJ

For the reaction below, S = 269 J/(mol·K) and H = 103.8 kJ/mol. Calculate the equilibrium constant at 25ºC. 3C(s) + 4 H2(g) ⇌ C3H8(g)

1.4 x 10^4

What is the percent dissociation of a weak acid if its initial concentration is 1.5 M and its Ka = 4.5 x 10^-4?

1.7%

What is the pH of a solution for which [Ba(OH)2] = 0.015 M?

12.48

Calculate the hydroxide ion concentration for an aqueous solution that has a pH of 3.45.

2.8 x 10^-11 M

What is the pH of a solution which is 0.0100 M in HA (a weak acid) and also 0.0020 M in NaA (Ka = 9.0 x 10^-6)?

4.35

What is the pH of a solution that contains 0.033 M boric acid, H3BO3? The Ka for boric acid is 5.4 x10^-10

5.37

The ionization constant, Kw, of water at 60 oC is 1.0 x 10^-13. What is the pH of pure water at this temperature?

6.50

Given 100.0 mL of a buffer that is 0.50 M in HOCl and 0.40 M in NaOCl, what is the pH after 10.0 mL of 1.0 M NaOH has been added? (Ka for HOCl = 3.5 x 10^-8)

7.55

A 1.50 L solution initially contains 0.100 M HClO2 and 0.150 M NaClO2. What is the pH of the resulting solution when 0.0500 moles of KOH (s) is added? (Assume no change in volume takes place.) Ka (HClO2) = 1.15 x 10^-2 A. 2.38 B. 1.51 C. 2.55 D. 1.35 E. 2.00

A

A reaction releases 250 kJ of heat but has a decrease in disorder of 800 J/K. Calculate G for this reaction at 27 ºC. Is the reaction spontaneous or non-spontaneous? A. -10 kJ, spontaneous B. -10 kJ, non-spontaneous C. +10 kJ, spontaneous D. +10 kJ, non-spontaneous

A

A solution is prepared by dissolving 0.23 moles of hydrofluoric acid and 0.27 moles of sodium fluoride in water sufficient to yield 63.95 mL of solution. What is the pH after the addition of 0.05 mol of HCl? Assume that the volume does not change. (Ka = 6.8 x 10-4 for hydrofluoric acid). A. 3.06 B. 3.27 C. 3.23 D. 3.11 E. 4.01

A

An aqueous solution of which of the following salts will give the most basic solution? A. NaOCl C. NaClO2 B. NaCl D. NaClO3

A

At 60°C, the value of Kw is 9.5 x 10-14 the pH of pure water at 60°C is 6.51 What is the pOH of pure water at 60°C? A. 6.51 B. 7.00 C. 7.49 D. 14.00 E. 9.50

A

At 60°C, the value of Kw is 9.5 x 10^-14 . What is the pH of pure water at 60°C? A. 6.51 B. 7.00 C. 7.49 D. 14.00 E. 9.50

A

In an aqueous solution which is 0.1 M sodium acetate, NaCH3COO, the concentration of hydronium ions [H3O+]is.... A. less than the [H3O+] in 0.1 M acetic acid. B. equal to the [H3O+] in 0.1 M acetic acid. C. greater than the [H3O+] in 0.1 M acetic acid. D. impossible to compare with the [H3O+] in 0.1 M acetic acid.

A

The figure below shows three acids HX, HY and HZ, (water molecules are omitted for clarity). Which acid has the largest Ka? (refer to the figure on page 2 of macs exam) A. HX B. HY C. HZ D. it depends on the amount of acid present.

A

What is the conjugate base of HSO4-? A. SO4^2- B. SO2 C. H2SO4 D. HSO3^- E. H2SO3

A

What is the pH of a 0.0150 M solution of calcium hydroxide? A. 12.48 B. 12.18 C. 1.82 D. 1.52 E. 11.87

A

What is the pH of a 0.55 M aqueous hypobromous acid, HBrO, at 25°C (Ka = 2.0 x 10-9)? A. 4.48 B. 8.96 C. 4.22 D. 0.26 E. 9.52

A

What is the pH of a 23.91 mL solution that contains 0.25 molal benzoic acid, C6H5COOH, and 0.75 molal sodium benzoate, C6H5COONa? (Ka of benzoic acid = 6.3 x 10-5) A. 4.68 B. 3.72 C. 10.28 D. 9.32 E. 6.35

A

What volume of 0.1250 M sodium hydroxide must be added to completely neutralize 25.00 mL of 0.1478 M sulfuric acid? A. 59.12 mL B. 29.56 mL C. 14.78 mL D. 2.956 x 103 mL E. 2.956 x 101 mL

A

Which of the following pairs of compounds is a conjugate acid-base pair? A. H2O and OHB. NaF and KF C. OH^- and H^+ D. H3PO4 and PO4^3- E. HIO4 and Ca(OH)2

A

A 30.0 mL sample of 0.150 M potassium hydroxide is titrated with 0.125 M perchloric acid solution. What is the pH after 35.0 mL of acid has been added? A. 12.10 B. 11.28 C. 7.00 D. 2.73 E. 2.15

B

A tank contains exactly 106 liters of pure water. 1.0 x 10-6 moles of HCl (g) is bubbled into this tank. What is the resulting pH? [HINT - analyze this problem carefully.] A. 2.0 B. 7.0 C. 8.0 D. 10.0 E. 12.0

B

Calculate the concentration of the hydronium ions in a solution at 25°C with a pOH of 4.223. A. 5.98 x 10^-5 M B. 1.67 x 10^-10 M C. 1.67 x 10^4 M D. 5.99 x 10^-19 M E. 1.00 x 10^-7 M

B

Calculate the percent ionization of formic acid (HCOOH) in a solution that is 0.311 M in formic acid and 0.189 M in sodium formate (NaHCOO). The pKa of formic acid is 3.752. A. 37.8 B. 0.0937 C. 11.3 D. 1.06 x 10^-3 E. 3.529

B

Consider the combustion of liquid propane (C3H8). What are the signs for ΔH, ΔS, and ΔG? A. +, -, + B. -, +, - C. +, -, - D. -, +, + E. -, -, +

B

Determine how many of the following salts are acidic: i) NH4Br, ii) KClO4, iii) Li2C2O4, iv) AlCl3, v) NaClO, vi) Na2SO3. A. 1 B. 2 C. 3 D. 4 E. 5

B

In the titration of a tribasic acid against a strong base, the pH at the third equivalence point will be: A. Equal to 7.0 B. Greater than 7.0 C. Less than 7.0 D. Exactly 2.5 E. Need to know if acid is strong or weak first

B

Suppose ΔG° equals 0. What then will be the value of the equilibrium constant, K? A. K = 0 B. K = 1 C. K = -1 D. 0 < K < 1 E. K > 1

B

The following image represents a spontaneous gaseous reaction at constant temperature. Predict if ΔH and ΔS are positive or negative. (refer to the picture on page 1) ΔH ΔS A. Positive Positive B. Negative Negative C. Positive Negative D. Negative Positive E. Can't be determined from the picture

B

The hydride anion (H- ) is a stronger base than the hydroxide anion. The product(s) of the reaction of the hydride anion with water is/are therefore: A. H3O^+ (aq) B. OH^-(aq) + H2 (g) C. OH^-(aq) + 2H+ (aq) D. H2O2 (aq) E. H3O^-(aq)

B

Which of the following solutions will have the lowest pH? A. 0.10 M HCN (Ka = 6.2 x 10^-10) B. 0.10 M HIO3 (Ka = 1.6 x 10^-1) C. 0.10 M HF (Ka = 6.8 x10^-4) D. 0.10 M CH3COOH (Ka = 1.8 x 10^-5) E. 0.10 M HNO2 (Ka = 7.1 x10^-4)

B

Which regions/s correspond/s to solutions having the greatest buffering capacity? (refer to the graph on page 8) A. 3, 4 B. 2 C. 2, 5 D. 4 E. 5

B

. What can be said about the spontaneity of the dimerization of sulfur in the gas phase? 2S(g) → S2(g) ΔHºf (kJ/mol) Sº (J/K*mol) S(g) 277 238 S2(g) 129 80. A. The formation of S2(g) (forward reaction) is spontaneous at all temperatures. B. The formation of S(g) (reverse reaction) is spontaneous at all temperatures. C. The formation of S2(g) (forward reaction) is spontaneous at low temperatures and the formation of S(g) (reverse reaction) is spontaneous at high temperatures. D. The formation of S(g) (reverse reaction) is spontaneous at low temperatures and the formation of S2(g) (forward reaction) is spontaneous at high temperatures.

C

.Which of the following pairs correctly ranks the compounds in terms of decreasing acid strength? A. HBrO2 > HBrO3 B. HIO > HClO C. H2Se > H2S D. SiH4 > PH3 E. H3C-COOH > F3C-COOH

C

An unknown acid is titrated with an NaOH solution of equal concentration, yielding the titration curve on the right. Based on this curve, which of the following could be the unknown acid? (refer to the 2nd graph on page 9) A. Hydrochloric acid (HCl) B. Chromic acid (H2CrO4; Ka1 = 0.182, Ka2 = 3.24 x 10^-7) C. Pyruvic acid (CH3COCOOH; Ka = 4.07 x 10^-3) D. Hydrazoic acid (HN3; Ka = 2.51 x 10^-5) E. Phenol (C6H5OH); Ka = 1.02 x 10^-10)

C

Consider the following gas-phase reaction of A2 (grey spheres) and B2 (black spheres) molecules. A2 + B2 ⇌ 2AB Which of the following reaction mixtures (not at equilibrium) has the largest (most positive) ΔG of reaction? (refer to problem 15 on macs review) A. Mixture I B. Mixture II C. Mixture III D. Mixtures I and II E. Mixtures I and III

C

In which of the following 0.10 M aqueous solutions does the weak acid exhibit the highest percent ionization? A. HC2H3O2 (Ka = 1.8 x 10-5) B. HNO2 (Ka = 4.5 x 10-4) C. HF (Ka = 6.8 x 10-4) D. HClO (Ka = 3.0 x 10-8) E. These will all exhibit the same percent ionization

C

Phosphoric acid undergoes three ionization reactions. Which of the following statements about this triprotic acid is TRUE? i. HPO4^2-(aq) is a stronger acid than H2PO4^- ii. PO4 3- (aq) is the strongest basic species iii. H2PO4 - (aq) is a stronger acid than H3PO4 (aq) iv. H2PO4 - (aq) is a stronger acid than HPO4^2- (aq) v. H2PO4^- (aq) is a stronger base than HPO4^2- (aq) A. i and ii B. ii and iii C. ii and iv D. iii and iv E. ii and v

C

To which of the following would the addition of an equal volume of 0.70 M NaOH lead to a solution having a lower pH? A. pure water B. 0.40 M HCl C. 0.80 M KOH D. 0.50 M NaNO3 E. None of the above

C

Walter White asks Jesse Pinkman: What is the pH of a 0.35 M aqueous solution of methylamine, (CH3NH2)? Help him with the math, knowing that the Kb of methylamine is 4.4 x 10^-4 . A. 10.00 B. 3.86 C. 12.08 D. 1.96 E. 13.24

C

Which is the NET IONIC EQUATION for the reaction between a weak acid and a strong base? A. H+ + OH- ⇄ H2O B. H+ + MOH ⇄ H2O + M+ C. HA + OH- ⇄ H2O + AD. HA + MOH ⇄ H2O + MA E. H+ + H- ⇄ H2

C

Which of the following is the most acidic Mn+ B. Mn3+ C. Mn5+ D. Mn2- E. Since all are Mn species, they should have equal acidity

C

Which of the following provides the correct order of acid strength? A. H2O > H2S B. HBrO3 > HBrO4 C. HCl > HF D. HSO4^- > H2SO4 E. None of the other answers is correct

C

Which of the following statements is INCORRECT regarding a 1.0 M solution of a strong acid HZ? [Z-] = [H+] [HZ] = 1.0 M [H+] = 1.0 M pH = 0.00

C

. HA is a weak acid. Which equation gives the equilibrium constant Kb for A-? A. HA (aq) + H2O (l) ⇄ H2A+ (aq) + OH- (aq) B. A^-(aq) + H3O^+ (aq) ⇄ HA (aq) + H2O (l) C. HA (aq) + OH^-(aq) ⇄ H2O (l) + A^- (aq) D. A^-(aq) + H2O (l) ⇄ HA (aq) + OH^- (aq) E. A^-(aq) + OH^-(aq) ⇄ HOA2-(aq)

D

A 0.0035 M aqueous solution of a particular compound has a pH of 2.46. Which of the following could this be? A. A weak base B. A strong base C. A weak acid D. A strong acid E. The salt of a strong base and a weak acid

D

A Chem 112 student performs a titration with equi-molar acid and base and obtains the titration curve shown on the right. This titration curve is an example of a: (refer to the graph on page 8) A. Strong acid being titrated with a weak base. B. Strong base being titrated with a strong acid. C. Weak acid being titrated with a strong base. D. Weak base being titrated with a strong acid. E. Polyprotic acid being titrated with a strong base.

D

A solution is made by dissolving 0.23 mol of chloroacetic acid (Ka = 1.36 x 10-3 ) and 0.27 mol of sodium chloroacetate in water to produce 500 mL of solution. The addition of 0.05 mol HCl to this solution causes the pH to drop slightly. The pH does not decrease drastically because the acid reacts with... A. H2O B. H3O+ C. Chloroacetic acid D. Chloroacetate ion E. Some other reason

D

Consider the following chemicals: H2O (g), H2 (g), Na (s), and H2O (l). For which members of this list is the Gibbs' Free Energy of Formation equal to zero? A. H2 (g) only B. H2 (g) and H2O (g) only C. Na (s) only D. H2 (g) and Na (s) only E. All except for H2O (g)

D

For the reaction C2H6 (g) → C2H4 (g) + H2 (g), ΔH° is 137 kJ and ΔS° 120 J/K at standard conditions. Assuming the values of ΔH° and ΔS° do not change significantly with temperature, this reaction will be A. Spontaneous at all temperatures B. Spontaneous only at low temperatures C. Nonspontaneous at all temperatures D. Spontaneous only at high temperatures E. Can't determine without knowing the temperature

D

The conversion C (diamond) → C (graphite) is "spontaneous". However, diamonds do not degrade under standard conditions (25°C, 1 atm), thus "diamonds are forever." Why is this? A. Diamond is thermodynamically stable B. Graphite rapidly changes back to diamond C. Diamond and graphite are at equilibrium D. Spontaneity implies nothing about the rate of the reaction E. The reaction is too fast to be observed

D

The decomposition reaction for phosphorous pentachloride, PCl5 (g) ⇄ PCl3 (g) + Cl2 (g), has Kp = 0.0211 at 160°C. What is ΔG° (in kJ/mol), for this reaction? A. 6.03 B. 0.137 C. 5.13 D. 13.9 E. -6.03

D

What is the conjugate acid of HPO4 2-? A. H3PO4 B. HPO4^3- C. HPO3^2- D. H2PO4^- E. H2PO4^2-

D

What is the pH of a solution that is 0.060 M in potassium propionate (KC3H5O2) and 0.085 M in propionic acid (HC3H5O2)? (Ka = 1.310-5 for propionic acid) A. 5.04 B. 4.88 C. -4.73 D. 4.73 E. 4.58

D

What is ΔG° for the reaction H2 (g) + F2 (g) → 2HF (g) at 298 K? Use the information below: H2 (g) F2 (g) HF (g) ∆Hf°(kJ mol-1) -268.61 S° (J mol-1 K-1) 130.58_202.70_173.51 A. -537.22 kJ B. +537.22 kJ C. +541.31 kJ D. -541.31 kJ E. -270.66 kJ

D

Which of the following combinations COULD produce a useful buffer in aqueous solution? A. H2SO4 and NaHSO4 B. Ca(NO3)2 and HNO3 C. HCl and NaCl D. HF and NaOH E. None of them is suitable

D

Which of the following is the most basic? A. Fe3+ (aq) B. Fe2+ (aq) C. Fe+ (aq) D. Fe (s) E. Since all are Fe species, they should have equal basicity

D

Which of the following is the weakest acid? A. HClO2 (Ka for HClO2 = 1.1 x 10-2 ) B. HNO3 (Kb for NO3^- → 0) C. HCN (pKb for CN- = 4.79) D. H3BO3 (pKa for H3BO3 = 9.27) E. H2S (Kb for HS- = 1.12 x 10^-7)

D

Which of the following pairs of substances can be used to make a buffer solution? A. NaI and HI B. KBr and HBr C. RbCl and HCl D. CsF and HF E. H3PO4 and Li2HPO4

D

Which of the following salts will dissolve in water to form a basic solution? (NH4Cl, Cu(NO3)2, K2CO3, NaF) A. NH4Cl and Cu(NO3)2 B. K2CO3 and NH4Cl C. NaF only D. NaF and K2CO3 E. NH4Cl only

D

You have the following bases and want to prepare a buffer solution with pH = 8.90. Which one do you choose? A. cinnoline Kb = 2.3 x 10^-12 B. pyridine Kb = 1.7 x 10^-9 C. ketamine Kb = 3.0 x 10^-7 D. codeine Kb = 1.6 x 10^-6 E. dibutylamine Kb = 1.8 x 10^-3

D

Liquid Plumber, a drain cleaner, has a pH of 14.32. What is the pOH and [OH-] of this solution? pOH [OH-] A. +0.32 2.1 M B. -0.68 4.8 M C. -0.32 0.48 M D. +0.68 4.8 M E. -0.32 2.1 M

E

The pKb of ammonia in water is 4.7. What is the pH of a 93.26 mL solution that contains 0.20 M ammonium ions and 0.10 M ammonia? (Shortcut hint: There's another form of the equation you need.) A. 5.0 B. 9.8 C. 9.3 D. 9.6 E. 9.0

E

Upon the addition of HCl, the pH of an aqueous solution changes from 4.0 to 2.0. Which of the following statements is TRUE? A. The concentration of H3O+ ions decreases by a hundred times B. The concentration of H3O+ ions increases by two times C. The concentration of OHions decreases by two times D. The concentration of OHions increases by two times E. The concentration of H3O+ ions increases by a hundred times

E

Which of the following combinations will produce the most useable buffer solution? A. HCl and NaCl B. H2SO4 and (NH4)2SO4 C. HI and NaI D. HNO2 and NaNO3 E. HNO2 and NaNO2

E

Which of the following is the weakest acid? A. HF (Ka = 6.8 x 10^ -4) B. HClO (Ka = 3.2 x 10^ -8) C. HNO2 (Ka = 4.5 x 10^ -4) D. HC2H3O2 (Ka = 1.8 x 10^ -5) E. HCN (Ka = 4.9 x 10^ -10)

E

Which of the following species can behave as Lewis Acids, but not as Brønsted-Lowry Acids? (H3O+, BF3, NH4^+, Ca2+, HF, H^-, Ne) A. Only BF3, Ca2+, and Ne B. Only HF, H- , and BF3 C. Only BF3 D. Only Ca2+ E. Only BF3 and Ca2+

E

Which of these statements is true about the spontaneity of reactions? A. A spontaneous reaction is one that proceeds rapidly B. A spontaneous reaction is one that doesn't occur immediately, but which can start without warning C. A nonspontaneous reaction is one that will occur only very slowly D. A spontaneous reaction is one that occurs instantaneously E. A spontaneous reaction is one that does not require an external energy source to proceed.

E

Which of the following has the HIGHEST value for [OH-]? A solution with a pH of 3.0 A 1.0 x 10-4 M solution of nitric acid A solution with a pOH value of 12.0 Pure water A 1.0 x 10-3 M solution of ammonium chloride

Pure water