Chem 2 Exam 3

A 0.40-mol sample of a diprotic acid, H 2A, is dissolved in 250 mL of water. The K a1 of this acid is 1.0 × 10 -5 and K a2 is 1.0 × 10 -10. Calculate the concentration of A 2- in this solution. 1.0 × 10-5 M 2.0 × 10-3 M 4.0 × 10-3 M 1.0 × 10-10 M 1.60 M

1.0 x 10-10

Determine the pH of a 0.037 M solution of H 2SO 4. The dissociation occurs in two steps. K a1 is extremely large; K a2 is 1.2 10 -2. 12.69 1.43 1.92 1.35 2.11

1.35

What is the equilibrium pH of a 0.287 M solution of H 3PO 4( aq)? ( K a1 = 7.5 × 10 -3, K a2 = 6.2 × 10 -8, K a3 = 4.8 × 10 -13) 1.37 3.87 12.32 6.43 7.21

12.32

The [OH -] in a 0.24 M pyridine (C 5H 5N; K b = 1.7 × 10 -9) solution is 4.1 × 10-10 M 2.0 × 10-5 M 0.24 M 8.4 × 10-5 M none of these

2.0 x 10-5

Given that the K a for HOCl is 3.48 10 -8, calculate the K value for the reaction of HOCl with OH -. 3.48 × 106 3.48 3.48 × 10-22 2.87 × 10-7 2.87 × 1021

3.48 X 106

Calculate the [H +] in a solution that has a pH of 2.44. 2.4 M 11.6 M 3.6 × 10-3 M 2.8 × 10-12 M none of these

3.6 x 10 -3

Calculate the [H +] in a solution that has a pH of 8.42. 3.8 × 10-9 M 2.6 × 10-6 M 8.4 × 10-9 M 9.3 × 10-1 M 7.5 × 10-1 M

3.8 x 10-9

Saccharin is a monoprotic acid. If the pH of a 4.59 × 10 -3 M solution of this acid is 2.53, what is the K a of saccharin? 8.7 × 10-6 1.9 × 10-3 5.3 × 10-3 2.9 × 10-3 none of these

5.3 x 10-3

The pH of a 0.21 M solution of a weak monoprotic acid, HA, is 2.92. Calculate the K a for this acid. (WRONG) 0.21 1.2 × 10-3 5.8 × 10-3 6.9 × 10-6 4.8 × 10-11

6.9 x 10-6

The two acid dissociation constants for sulfurous acid, H 2SO 3, are 1.3 10 -2 and 6.3 10 -8 at 25ºC. The base constant, K b, or hydrolysis constant for HSO 3 - is: 1.3 10-2 6.3 10-8 8.2 10-10 7.7 10-13 6.2 10-22

7.7 x 10 -13

Determine the concentration of a solution of the weak acid HClO 2 ( K a = 1.10 10 -2) if it has a pH of 1.140. 0.477 M 0.0724 M 6.59 M 12.9 M 0.954 M

A

Select the answer that best describes an aqueous solution made from each of the following substances:Reference: Ref 14-4 solid aluminum chloride (AlCl 3) acidic basic neutral cannot tell none of these (A-D)

A

Select the answer that best describes an aqueous solution made from each of the following substances:Reference: Ref 14-4 solid ammonium perchlorate (NH 4ClO 4) For NH 4 +, K a = 5.6 × 10 -10; for ClO 4 -, K b 10 -21. acidic basic neutral cannot tell none of these (A-D)

A

The pH of a 1.0 M aqueous solution of NaCl is: 7.0 greater than 7.0 less than 7.0 not enough information given none of these (A-D)

A

Which is the strongest acid of the following? HClO2 HClO HBrO HIO HOA

A

Which of the following aqueous solutions will have the highest pH? For NH 3, K b = 1.8 × 10 -5; for C 2H 3O 2 -, K b = 5.6 × 10 -10. 2.0 M NaOH 2.0 M NH3 2.0 M HC2H3O2 2.0 M HCl all the same

A

Which of the following species cannot act as a Lewis acid? NH4+ H+ BF3 BeCl2 Ag+

A

Which of the following species cannot act as a Lewis base? (WRONG) S2- SH- BH3 H2S NH3

A

Which of the following species is present in the greatest concentration in a 0.100 M H 2SO 4 solution in H 2O? H3O+ HSO4- H2SO4 All species are in equilibrium and therefore have the same concentration. SO42-

A

Calculate the pH of the following aqueous solution: 0.99 M H 2S (p K a1 = 7.00; p K a2 = 12.89) 10.50 3.50 7.00 7.00 none of these

B

If an acid, HA, is 10.1% dissociated in a 1.0 M solution, what is the K a for this acid? 1.1 × 10-1 1.1 × 10-2 1.0 × 10-1 8.8 × 101 none of these

B

In a solution prepared by dissolving 0.100 mole of propanoic acid in enough water to make 1.00 L of solution, the pH is observed to be 2.768. The K a for propanoic acid (HC 3H 5O 2) is: 1.71 × 10-3 2.96 × 10-5 1.74 × 10-2 3.38 × 10-10 none of these

B

In which of the following reactions does the H 2PO 4 - ion act as an acid? H3PO4 + H2O → H3O+ + H2PO4- H2PO4- + H2O → H3O+ + HPO42- H2PO4- + OH- → H3PO4 + O2- The ion cannot act as an acid. Two of these.

B

Select the answer that best describes an aqueous solution made from each of the following substances:Reference: Ref 14-4 solid sodium carbonate (Na 2CO 3) acidic basic neutral cannot tell none of these (A-D)

B

The pH of a 0.150 M solution of a weak base is 10.98. Calculate the pH of a 0.0874 M solution of the base. 3.14 10.86 7.73 6.27 none of these

B

The pain killer morphine is a weak base when added to water. The K b is 1.6 × 10 -6. What is the pH of a 4.89 × 10 -3 M solution of morphine? 4.05 9.95 5.89 9.80 none of these

B

What is the equilibrium concentration of HPO 4 2- in a 0.789 M solution of H 3PO 4( aq)? ( K a1 = 7.5 × 10 -3, K a2 = 6.2 × 10 -8, K a3 = 4.8 × 10 -13) (WRONG) 2.2 × 10-4 M 7.3 × 10-2 M 4.8 × 10-13 M 6.2 × 10-8 M 6.2 × 10-7 M

B

What volume of water must be added to 11.0 mL of a pH 2.0 solution of HNO 3 in order to change the pH to 4.0? (WRONG) 11.0 mL 89 mL 109 mL 1.09 × 103 mL 28 mL

B

When 2.0 × 10 -2 mol of nicotinic acid (a monoprotic acid) is dissolved in 350 mL of water, the pH is 3.05. Calculate the K a of nicotinic acid. 1.6 × 10-2 1.4 × 10-5 5.6 × 10-2 4.2 × 10-5 none of these

B

Which of the following is not true for a solution at 25°C that has a hydroxide concentration of 2.5 10 -6 M? Kw = 1 × 10-14 The solution is acidic. The solution is basic. The [H+] is 4.0 × 10-9 M. The Kw is independent of what the solution contains.

B

alculate the pH of a 0.04 M solution of ascorbic acid ( K a1 = 7.9 10 -5; K a2 is 1.6 10 -12). 11.2 2.8 5.5 8.5 11.8

B

n the reaction: CaO( s) + CO 2( g) → CaCO 3( s) Ca2+ acts as a Lewis acid and CO32- acts as a Lewis base. O2- acts as a Lewis base and CO2 acts as a Lewis acid. O2- acts as a Lewis base and Ca2+ acts as a Lewis acid. CaO is the Lewis acid and CaCO3 is its conjugate base. CO2 is the Lewis acid and CaCO3 is its conjugate base.

B

A 0.108 M solution of the salt NaA has a pH of 8.40. Calculate the K a value of the acid HA. 5.8 × 10-11 4.3 × 10-10 1.7 × 10-4 6.8 × 101 none of these

C

A monoprotic weak acid when dissolved in water is 0.59% dissociated and produces a solution with a pH of 3.23. Calculate the K a of the acid. 5.9 × 10-3 10.0 × 10-2 3.5 × 10-6 Need to know the initial concentration of the acid. None of these.

C

Calculate the pH of a 2.8 × 10 -3 M KOH solution. 2.55 12.45 11.45 1.55 10.45

C

Calculate the pH of the following aqueous solution: 0.96 M NaF (p K a for HF = 3.14) 5.44 3.12 8.56 10.88 none of these

C

Consider the following reactions: a) Al 3+ + 6H 2O Al(OH 2) 6 3+ b) Al(OH 2) 6 3+ Al(OH)(OH 2) 5 2+ + H + c) OCl - + H 2O HOCl + OH - d) CN - + H + HCN e) none of these Reference: Ref 14-1 Which is associated with the definition of K b? a b c d e

C

HOAc K a = 1.8 × 10 -5 H 2CO 3 K a1 = 4.3 × 10 -7 K a2 = 5.6 × 10 -11 Which of the following 0.01 M solutions has the highest pH? HOAc NaOAc Na2CO3 H2CO3 NaHCO3

C

If K a for HCN is 6.21 × 10 -10, what is K b for CN -? Note: CN - + H 2O HCN + OH - 6.21 × 10-24 6.21 × 104 1.61 × 10-5 1.24 × 10-9 none of these

C

Select the answer that best describes an aqueous solution made from each of the following substances:Reference: Ref 14-4 solid ammonium acetate (NH 4C 2H 3O 2). For NH 4 +, K a = 5.6 × 10 -10; for C 2H 3O 2 -, K b = 5.6 × 10 -10. acidic basic neutral cannot tell none of these (A-D)

C

The [H 3O +] of a 0.33 M solution of NH 4Cl in H 2O at 25°C is ( K b for NH 3 = 1.8 10 -5): 1.8 × 10-10 M 2.4 × 10-3 M 1.4 × 10-5 M 0.33 M none of these

C

The following question refers to a solution that contains 1.62 M hydrofluoric acid, HF ( K a = 7.2 × 10 -4), and 3.00 M hydrocyanic acid, HCN ( K a = 6.2 × 10 -10). Determine the [CN -] at equilibrium. 1.9 × 10-9 M 3.4 × 10-2 M 5.4 × 10-8 M 6.2 × 10-10 M none of these

C

Which of the following would give the highest pH when dissolved in water to form a 0.10 M solution? a strong acid a weak acid the potassium salt of a weak acid the potassium salt of a strong acid the ammonium salt of a strong acid

C

The following three equations represent equilibria that lie far to the right. HNO 3( aq) + CN -( aq) HCN( aq) + NO 3 -( aq) HCN( aq) + OH -( aq) H 2O( l) + CN -( aq) H 2O( l) + CH 3O -( aq) CH 3OH( aq) + OH -( aq) Identify the strongest base. CH3O- CH3OH CN- H2O NO3-

CH3O

Calculate the [H +] in 1.0 M solution of Na 2CO 3 (for H 2CO 3, K a1 = 4.3 10 -7; K a2 = 5.6 10 -11). 7.5 × 10-6 M 6.6 × 10-4 M 1.3 × 10-2 M 7.5 × 10-13 M none of these

D

Determine the percent dissociation of a 0.17 M solution of hypochlorous acid, HClO. The K a for the acid is 3.5 × 10 -8. 3.5 × 10-6 % 6.0 × 10-9 % 7.7 × 10-3 % 4.5 × 10-2 % 1.1 × 10-2 %

D

How many moles of benzoic acid, a monoprotic acid with K a = 6.4 10 -5, must be dissolved in 250. mL of H 2O to produce a solution with pH = 2.19? (WRONG) 0.65 0.00161 0.16 25 none of these

D

The salt BX, when dissolved in water, produces an acidic solution. Which of the following could be true? HX is a weak acid. HX is a strong acid. The cation B+ is a weak acid. All of the above could be true. Only A and C could be true.

D

Which factor listed below is most important in determining the strength of an oxyacid? the size of the molecule the ability of the molecule to change atomic orientation the identity of the central atom in the molecule the number of oxygen atoms present in the molecule none of these

D

Which of the following is the correct order for increasing pHs for equimolar solutions of HNO 3, KCl, NH 4Cl, KOH, and NaC 2H 3O 2? ( K a for HC 2H 3O 2 is 1.80 10 -5, K a for NH 4 + is 5.56 10 -10). KCl, NH4Cl, HNO3, KOH, NaC2H3O2 HNO3, KCl, NH4Cl, KOH, NaC2H3O2 NH4Cl, HNO3, KCl, KOH, NaC2H3O2 HNO3, NH4Cl, KCl, NaC2H3O2, KOH none of these

D

Which of the following statements are true? The pH of a strong acid is always lower than the pH of a weak acid. The pH of a solution can never be negative. For a conjugate acid-base pair, Ka = 1/Kb. At least two of the statements A-C are true. All of the statements A-C are false.

D

Consider a solution made by mixing HCN ( K a = 6.2 × 10 -10) with HC 2H 3O 2 ( K a = 1.8 × 10 -5) in aqueous solution. What are the major species in solution? H+, CN-, H+, C2H3O2-, H2O HCN, H+, C2H3O2-, H2O H+, CN-, HC2H3O2, H2O H+, CN-, H+, C2H3O2-, OH-, H2O HCN, HC2H3O2, H2O

E

Consider the following reaction: AgBr( s) + 2CN -( aq) → Ag(CN) 2 -( aq) + Br -( aq) The species that are acting as a Lewis acid and Lewis base, respectively, are AgBr and Ag(CN)2- Ag(CN)2- and Ag+ Ag+ and Br- Br- and CN- Ag+ and CN-

E

Given the following acids and K a values: HClO 4 HOAc HCN HF 1 10 7 1.76 10 -5 4.93 10 -10 3.53 10 -4 What is the order of increasing base strength? CN-, F-, OAc-, ClO4- CN-, OAc-, F-, ClO4- CN-, ClO4-, F-, OAc- ClO4-, OAc-, CN-, F- ClO4-, F-, OAc-, CN-

E

True or false: The species Cl - is not a good base in aqueous solution. True. This is because Cl- is the conjugate base of a weak acid. False. The species Cl- is a good base in aqueous solution because it is the conjugate base of a strong acid. True. This is because Cl- is a good proton donor. False. The species Cl- is a good base in aqueous solution because of its high electronegativity. True. This is because water has a stronger attraction for protons than does Cl-

E

What is the equilibrium concentration of H 2PO 4 - in a 0.682 M solution of H 3PO 4( aq)? ( K a1 = 7.5 × 10 -3, K a2 = 6.2 × 10 -8, K a3 = 4.8 × 10 -13) (WRONG) 2.1 × 10-4 M 6.8 × 10-2 M 7.2 × 10-2 M 7.5 × 10-3 M 6.2 × 10-8 M

E

What is the pOH of pure water at 90 oC? ( K w at 90 oC = 3.73 × 10 -13) 7.786 7.000 14.000 12.428 6.214

E

Which of the following is true about the pH of a solution of sulfuric acid? If the solution is dilute the pH can not be calculated. If the solution is dilute the pH is completely controlled by the first dissociation. If the solution is dilute the pH is completely controlled by the second dissociation. If the solution is concentrated the pH is partially controlled by the second dissociation. If the solution is dilute the pH is partially controlled by the second dissociation.

E

Which of the following species cannot act as a Lewis base? N3- NH2- NH2- NH3 NH4+

E

Which of the following is the strongest base? ( K b for NH 3 is 1.8 10 -5, K a2 for H 2SO 4 is 1.2 10 -2, K a3 for H 3PO 4 is 4.8 10 -13) NH 3, HSO 4 -, PO 4 3-, or NO 3 - NH3 HSO4- NO3- PO43- Two of these are equally strong.

PO43

A 8.5 10 -3 M solution of a weak acid is 4.6% dissociated at 25ºC. In a 8.5 10 -4 M solution, the percentage of dissociation would be the same > 4.6% < 4.6% zero need to know the Ka of the acid to answer this

b

Calculate the pH of a 0.13 M solution of NH 4Cl. ( K b for NH 3 = 1.8 10 -5) 8.93 5.07 10.14 3.86 0.89

b

Consider the following reactions: a) Al 3+ + 6H 2O Al(OH 2) 6 3+ b) Al(OH 2) 6 3+ Al(OH)(OH 2) 5 2+ + H + c) OCl - + H 2O HOCl + OH - d) CN - + H + HCN e) none of these Reference: Ref 14-1 Which is associated with the definition of K a? a b c d e

b

Calculate the pOH of a 5.3 M solution of HCl. -0.72 13.28 14.72 0.72 -0.94

c

The autoionization of water, as represented by the below equation, is known to be endothermic. Which of the following correctly states what occurs as the temperature of water is raised? H 2O( l) + H 2O( l) H 3O +( aq) + OH -( aq) The pH of the water does not change, and the water remains neutral. The pH of the water decreases, and the water becomes more acidic. The pH of the water decreases, and the water remains neutral. The pH of the water increases, and the water becomes more acidic. The pH of the water increases and the water remains neutral.

c

The equilibrium constants ( K a) for HCN and HF in H 2O at 25°C are 6.2 × 10 -10 and 7.2 10 -4, respectively. The relative order of base strengths is: F- > H2O > CN- H2O > F- > CN- CN- > F- > H2O F- > CN- > H2O none of these

c

Which of the following solutions contains the strongest acid? 5.00 M HCN (Ka = 6.2 × 10-10) 3.50 M H2C6H6O6 (Ka1 = 7.9 × 10-5, Ka2 = 1.6 × 10-12). 2.50 M HC2H3O2 (Ka = 1.8 × 10-5) 4.00 M HOCl (Ka = 3.5 × 10-8) 1.00 M HF (Ka = 7.2 × 10-4)

e