Chem 108 Midterm 3

A solution of hydrochloric acid (HCl, 25.00 mL) was titrated to the equivalence point with 34.55 mL of 0.1020 M sodium hydroxide. What was the concentration of the hydrochloric acid? 0.07048 M d. 0.0353 M 0.1410 M e. 0.0533 M 0.2819 M

(m1v1=m2v2)= 0.1410

Consider a solution initially containing 0.40 mol fluoride anion and 0.30 mol of hydrogen fluoride (HF). How many moles of hydrogen fluoride are present after addition of 0.20 mol of HCl to this solution? a) 0.20 molb) 0.30 molc) 0.40 mold) 0.50 mole) none of the above

0.50 mol

Manganese carbonate (MnCO3) has low solubility in neutral water (8 mg/L), but dissolves completely in water whose pH is low. Which of the following explanations are true? 1. At low pH, H+ continuously and irreversibly removes carbonate ion 2. At low pH, OH- continuously removes Mn2+ ion 3. All solids always become completely soluble in acidic solution a) 1 only b) 2 only c) 3 only d) 1 and 3 only e) 2 and 3 only

1 only

What is the solubility of barium sulfate in otherwise pure water? The Ksp value for barium sulfate is 1.1 ́ 10-10. 7.4 ́10-6 M d. 2.2 ́10-9 M 5.5 ́10-11 M e. 1.1 ́10-10 M 1.0 ́10-5M

1.0 ́10-5M

What is the solubility of barium sulfate in a solution also containing 0.050 M sodium sulfate (which is fully soluble)? The Ksp value for barium sulfate is 1.1 ́ 10-10. 7.4 ́10-6 M d. 2.2 ́10-9 M 5.5 ́10-11 M e. 1.1 ́10-10 M c. 1.0 ́10-5M

2.2 ́10-9 M

72. The solubility of CaF2 is 3.9 x 10-11 mol/L. What is the Ksp of CaF2? a) 3.9 x 10-11 b) 6.2 x 10-6 c) 3.4 x 10-4 d) 2.1 x 10-4 e) none of the above

3.9 x 10-11

Lead pipes were used at one time for delivering drinking water. What is the maximum possible concentration of lead in this water if it comes from lead(II) hydroxide (Ksp = 2.8 ́ 10-16) dissolving from the surface of the pipes? Note the EPA limit on lead in drinking water is 7.2 ́ 10-8 M. 4.1 ́10-6 M d. 5.1 ́10-6M 1.6 ́10-8 M e. 8.3 ́10-9M 6.5 ́10-6M

4.1 ́10-6 M

Purveyors of salts from the Dead Sea advertise that it is healthy to bathe in a saturated solution of magnesium chloride (MgCl2, 95.21 g/mol, Ksp = 740). How much magnesium chloride would you have to purchase to make up 10.0 L of bath water saturated with magnesium chloride? 9.0 kg d. 5.4 kg 12kg e. 7.2kg 57kg

5.4 kg

The solubility of AgBr is 5.4 x 10-13 mol/L. What is the Ksp of AgBr? a) 5.4 x 10-13b) 7.3 x 10-7c) 9.5 x 10-5d) 3.0 x 10-10e) none of the above

5.4 x 10-13

The solubility of PbBr2 is 0.427 g per 100 mL of solution at 25°C. Determine the value of the solubility product constant for this strong electrolyte. 5.4 ́ 10-4 d. 1.6 ́ 10-6 2.7 ́ 10-4 e. 6.3 ́ 10-6 3.1 ́ 10-6

6.3 ́ 10-6

Stalactites—the long, icicle-like formations that hang from the ceilings of caves—are formed from calcium carbonate. The Ksp of calcium carbonate is 4.5 ́ 10-9. What is the concentration of calcium ions in a saturated calcium carbonate solution? a. 0.00104 M d. 2.25 ́ 10-9 M b. 4.5 ́10-9 M e. 4.5 ́10-5 M c. 6.7 ́10-5M

6.7 ́10-5M

Which of the following compounds would not have a pH dependent solubility? a. Fe(OH)2 d. PbBr2 b. Mn(N3)2 e. AgCN c. AgF

AgF

Which of the following compounds would not have a pH dependent solubility? a. Mg(OH)2 d. Na2O b. PbS e. PbS c. AgI

AgI, PbS

Explain how a buffer solution manages to stabilize the pH against the addition of acid, base, or additional solvent (dilution).

Answer: A buffer consists of a weak acid and its conjugate base in roughly equal amounts. If acid is added to the solution, it is consumed by the conjugate base. If base is added to the solution, it is consumed by the weak acid. If the amounts are such that the ratio of conjugate base/weak acid concentrations doesn't change much, then the pH doesn't change much. Dilution does not affect the pH because this concentration ratio doesn't change upon dilution.

A solution that contains a weak acid and its conjugate base in roughly equal concentrations is _____________ (choose one). Select one: a. Neither acidic or basic. b. A half-acid solution. c. A buffer. Correct d. A heterogeneous mixture. e. Neutral.

C. A buffer

If you start with 80.0 mL of 0.40 M HNO3, calculate the [H+] concentration following addition of 40.0 mL of 0.60 M KOH. a) 0.0667 Mb) 1.00 x 10-7 Mc) 0.100 Md) 1.50 x 10-13 Me) none of the above

H+ =0.0667 moles

When lead chloride (PbCl2) is placed in otherwise pure water, enough dissolves such that the concentration of lead ions becomes 0.036 M. What is the Ksp for lead chloride (PbCl2)?

K =1.9 ́10-4

The solubility product for an insoluble salt with the formula MX2 is written as , where x is the molar solubility. a. Ksp=x2 d. Ksp=2x3 b. Ksp=4x3 e. Ksp=2x2 c. Ksp = 4x2

Ksp=2x2

Which of the following statements is FALSE? Any solid that produces a basic anion will become more soluble at low pH Low pH increases solubility for solids that produce basic anions, because the acid reduces the concentration of the basic anion. LeChatelier then forces more solid to dissolve, resulting in elevated concentration of the cation. For solids that produce basic anions, the concentration of anion is lower than the concentration of the cation at low pH For metal hydroxides, solubility decreases at high pH where hydroxide concentration is high For solids with nonbasic anions like chlorides or bromides, solubility is still higher at low pH.

Low pH increases solubility for solids that produce basic anions, because the acid reduces the concentration of the basic anion. LeChatelier then forces more solid to dissolve, resulting in elevated concentration of the cation.

Consider a solution initially containing 0.300 mol of hydrogen fluoride (HF). How many grams of NaF (42.0 g/mol) would be needed to set the pH = 3.00? (HF, Ka = 7.2 ́ 10-4)?

NaF grams= 9.128

ConsiderasaturatedsolutionofAgClinwater.Comparedtotheoriginalconcentrationsofthe[Ag+]and[Cl-],how would the concentrations be different after some NaCl was added to the solution? a. The resulting [Ag+] and [Cl-] would both end up higher than they were originally. b. The resulting [Ag+] and [Cl-] would both end up lower than they were originally. c. The resulting [Ag+] would be larger, but the resulting [Cl-] would be smaller. d. The resulting[Ag+] would be smaller, but the [Cl-] would be larger. e. [Ag+] and [Cl-] would remain the same because the solution is saturated.

The resulting[Ag+] would be smaller, but the [Cl-] would be larger.

Consider a solution initially containing 0.40 mol fluoride anion and 0.30 mol of hydrogen fluoride (HF). If 0.40 mol of HCl are added to this solution, which of the following statements is FALSE? a) You will still have a buffer solution at the end, since you'll still have significant amounts of both weak base and conjugate weak acid b) The pH will have shifted to a lower pH c) You'll essentially have a weak acid solution situation, with 0.7 mol HF at the end. d) You will no longer have a buffer solution, since all of the weak base will have reacted with the HCl. The buffer capacity was exhausted. e) none of the above

You will still have a buffer solution at the end, since you'll still have significant amounts of both weak base and conjugate weak acid

If you start with 80.0 mL of 0.40 M HNO3, calculate the [H+] concentration following addition of 40.0 mL of 0.60 M KOH. a) 0.0667 Mb) 1.00 x 10-7 Mc) 0.100 Md) 1.50 x 10-13 Me) none of the above

a) 0.0667 M

Consider a solution initially containing 0.50 mol ammonia (NH3) and 0.30 mol of ammonium ion (NH4+). How many moles of ammonia and how many moles of ammonium ion are present after addition of 0.20 mol of HCl to this solution? a) 0.30 mol NH3, 0.50 mol NH4+ a) 0.50 mol NH3, 0.50 mol NH4+ a) 0.30 mol NH3, 0.20 mol NH4+ a) 0.70 mol NH3, 0.10 mol NH4+ e) none of the above

a) 0.30 mol NH3, 0.50 mol NH4+

Consider a solution initially containing 0.500 mol ammonia (NH3) and 0.300 mol of ammonium ion (NH4+). How many moles of ammonia and how many moles of ammonium ion are present after addition of 40 mL of 0.800M NaOH to this solution? a) 0.532 mol NH3, 0.268 mol NH4+ a) 0.532 mol NH3, 0.332 mol NH4+ a) 0.468mol NH3, 0.268 mol NH4+ a) 0.700 mol NH3, 0.100 mol NH4+ e) none of the above

a) 0.532 mol NH3, 0.268 mol NH4+

Which of the following combinations would give a pH of 7.00 at the "equivalence point" (when equal moles of each have been added)? a) HCl + KFb) HCN + NaOH c) HF + HCld) HCl + KOH

a) HCl + KF

Consider a solution initially containing 0.40 mol fluoride anion and 0.30 mol of hydrogen fluoride (HF). If 0.20 mol of HCl are added to this solution, which of the following statements is FALSE? a) You will still have a buffer solution at the end, since you'll still have both weak base and conjugate weak acid b) The pH will have shifted to a lower pH c) You'll have more moles of HF at the end than what you began with d) You will no longer have a buffer solution, since all of the weak base will have reacted with the HCl. e) none of the above

a) You will still have a buffer solution at the end, since you'll still have both weak base and conjugate weak acid

When the following chemicals are mixed, each in 1 liter of water, which would give a basic pH at the end? a) 1 mole of KOH and 1 mole of HF b) 1.0 mole of KOH and 1.0 mole of HCl c) 1 mole of HCl and 1 mole of NH3 d) 0.5 mole of KOH and 1.0 mole of HCl

a. 1 mole of KOH and 1 mole of HF

When placed in 1 L of water, which of the following combinations would give a buffer solution? (Remember, in some cases they might react with each other...) 1) 0.5 mol HClO and 0.5 mol NaClO 2) 0.5 mol HBr and 0.5 mol NaF 3) 0.5 mol HBr and 1.0 mol NaF 4) 0.5 mol HBr and 1.0 mol NaOH a) 1 only b) 1 and 2 only c) 1 and 3 only d) 3 and 4 only e) all would give buffer solutions

a. 1 only

Which of the following can be mixed together in water to produce a buffer solution? a. HClO4 and NaClO4 d. H3PO4 and NaH2PO4 b. HNO3 and NaNO3 e. HCl and NaCl c. H2SO4 and NaHSO4

a. HClO4 and NaClO4

Which of the following would be the best choice for preparing a buffer with a pH = 8.0? a. a solution of formic acid and sodium formate, Ka = 1.8 ́ 10-4 b. a solution of acetic acid and sodium acetate, Ka = 1.8 ́ 10-5 c. a solution of hypochlorous acid and sodium hypochlorite, Ka = 3.5 ́ 10-8 d. a solution of boric acid and sodium borate, Ka = 5.8 ́ 10-10 e. All of these solutions would be equally good choices for making this buffer.

a. a solution of formic acid and sodium formate, Ka = 1.8 ́ 10-4

Which combination of solutions is the best choice for making a buffer solution? a. equal volumes of 1 M ammonia (NH3) and 0.001 M ammonium chloride (NH4Cl) b. equal volumes of 0.5 M hydrochloric acid (HCl) and 0.5 M sodium hydroxide (NaOH) c. equal volumes of 0.5 M hydrochloric acid (HCl) and 0.5 M sodium chloride (NaCl) d. equal volumes of 2 M ammonia (NH3) and 1 M hydrochloric acid (HCl) e. equal volumes of 2 M ammonium chloride (NH4Cl) and 1 M hydrochloric acid (HCl)

a. equal volumes of 1 M ammonia (NH3) and 0.001 M ammonium chloride (NH4Cl)

Consider a solution that contains 0.50 moles of KF and 0.50 moles of HF in 1.0 L of water. If 0.10 mol of NaOH is added to this buffer solution, the pH of the solution will get slightly change more drastically because the NaOH reacts with the present in the buffer solution. a) higher, KF b) higher, HF c) lower, KF d) lower, HF

b) higher, HF

To simulate the pH of blood, which is 7.4, an undergraduate researcher in a biology lab produced a buffer solution by dissolving sodium dihydrogen phosphate (NaH2PO4, Ka = 6.2 ́ 10-8) and sodium hydrogen phosphate (Na2HPO4) together in an aqueous solution. What mole ratio of Na2HPO4/NaH2PO4 did she need to use? a. 1.2 d. 1.0 b. 1.6 e. 0.96 c. 0.90

b. 1.6

At what point in the following titration curve for a weak acid being titrated with a strong base is the pH equal to the pKa of the acid? The x-axis scale goes from 0.0 mL to 20.0 mL. The sharp rise is at 10.0 mL. a. 0.0 mL d. 10.0 mL b. 5.0 mL e. 18.0 mL c. 9.0 mL

b. 5.0 mL

Glycolic acid, which is a monoprotic acid and a constituent in sugar cane, has a pKa of 3.9. A 25.0 mL solution of glycolic acid is titrated to the equivalence point with 35.8 mL of 0.020 M sodium hydroxide solution. What is the pH of the resulting solution at the equivalence point? a. 5.10 d. 4.92 b. 7.98 e. 9.08 c. 8.72

b. 7.98

What reaction occurs as a hydrochloric acid solution is added to a solution containing equal concentrations of acetic acid and sodium acetate? a. CH3COOH + H+ ® CH3COOH2+ d. 2CH3COO- + 2H+ ® CH3COO + H2 b. CH3COO- + H+ ® CH3COOH e. CH3COOH + H+ ® CH3CO+ + H2O c. CH3COOH + HCl ® CH3COO- + H2Cl+

b. CH3COO- + H+ ® CH3COOH

Which of the following is not a buffer system?A solution containing roughly equal concentrations of a. fluoride ion and hydrofluoric acid. b. bromide ion and hydrobromic acid. c. phosphate ion and hydrogen phosphate ion. d. carbonate ion and hydrogen carbonate ion. e. phosphoric acid and dihydrogen phosphate ion.

b. bromide ion and hydrobromic acid.

Research with biochemical systems commonly requires buffers because a. that's just the way it is. b. proteins have a critical pH dependence in their structure and function. c. proteins decompose into constituent amino acids outside a certain pH range. d. proteins are buffers. e. salts are involved.

b. proteins have a critical pH dependence in their structure and function.

Consider a solution initially containing 0.400 mol fluoride anion and 0.300 mol of hydrogen fluoride (HF). How many moles of hydrogen fluoride are present after addition of 70.0 mL of 0.600M HCl to this solution? a) 0.400 mol fluoride, 0.300 mol HF b) 0.442 mol fluoride, 0.258 mol HF c) 0.358 mol fluoride, 0.342 mol HF d) 0.213 mol fluoride, 0.567 mol HF e) none of the above

c) 0.358 mol fluoride, 0.342 mol HF

An initial pH of 9.5 and an equivalence point at pH 4.5 correspond to a titration curve for a a) strong acid to which strong base is added b) strong base to which strong acid is added c) weak acid to which strong base is added d) weak base to which strong acid is added

c) weak acid to which strong base is added

When the following chemicals are mixed, each in 1 liter of water, which would give an acidic pH at the end? a) 1 mole of KOH and 1 mole of NaF b) 1 mole of NH4+ and 1 mole of NaOH c) 1 mole of HCl and 1 mole of NH3 d) 1 mole of KOH and 0.5 mole of HCl

c. 1 mole of HCl and 1 mole of NH3

13. Identify all the correct statements about an acid-base buffer solution. I. It can be prepared by combining a strong acid with a salt of its conjugate base. II. It can be prepared by combining a weak acid with a salt of its conjugate base. III. It can be prepared by combining a weak base with its conjugate acid. IV. The pH of a buffer solution does not change when the solution is diluted. V. A buffer solution resists changes in its pH when an acid or base is added to it. a. I,II,andIV d. I,II,IV,andV b. II, III, and V e. II, III, and IV c. II, III, IV, and V

c. II, III, IV, and V

What is the pH of a buffer solution where [HA] = [A-]? a. pH=1 d. pH=pOH b. pH=Ka e. pH=7.0 c. pH = pKa

c. pH = pKa

As the pH decreases, the solubility of __________ would increase. a lead(II) chloride d mercury(I) bromide b silver iodate e silver chloride c calcium carbonate

calcium carbonate

When an acetic acid solution is titrated with sodium hydroxide, the slope of the titration curve (pH vs volume of NaOH added) increases when sodium hydroxide is first added. This change shows that . a. nothing is happening during this part of the titration. b. the reaction is very slow during this part of the titration. c. a more concentrated solution of NaOH needs to be present to initiate the reaction. d. acetic acid is being converted to sodium acetate. e. the pH is not affected until all the acetic acid is consumed.

d. acetic acid is being converted to sodium acetate.

Halfwaytotheequivalencepointinatitrationcurveofaweakacidwithastrongbase, nothing is happening yet. d. pH = pKa of the indicator. the pH = pKa of the weak acid. e. the pH has not yet changed. pH = 3.5 exactly.

d. pH = pKa of the indicator.

Calculate the pH of a solution containing 0.40 mol fluoride anion and 0.30 mol of hydrogen fluoride (HF). (HF, Ka = 7.2 ́ 10-4)? a) 0.20 mol b) 0.30 mol c) 0.40 mol d) 0.50 mol e) none of the above

e) none of the above

Which one of the following would make the best buffer? (Ac = acetate, CH3CO2) a. a solution of hydrochloric acid and sodium chloride, HCl and NaCl b. a solution of acetic acid and ammonia, NaAc and NH3 c. a solution of acetic acid and ammonium chloride, HAc and NH4Cl d. a solution of sodium acetate and ammonium chloride, NaAc and NH4Cl e. a solution of ammonia and ammonium chloride, NH3 and NH4Cl

e. a solution of ammonia and ammonium chloride, NH3 and NH4Cl

How many moles of sodium acetate must be added to 500 mL of 0.25 M acetic acid solution to produce a buffer with a pH of 4.94? The pKa of acetic acid is 4.74. a. 0.011 moles d. 0.198 moles b. 0.021 moles e. 0.206 moles c. 0.125 moles

moles of sodium acetate (base) = 0.198 moles

If you start with 80.0 mL of 0.40 M HNO3, calculate the pH following addition of 50.0 mL of 0.80 M KOH. a) 3.4b) 7.0c) 12.8d) 13.1

pH= 12.79

Consider a solution initially containing 0.40mol fluoride anion and 0.30 mol of hydrogen fluoride (HF).What is the pH after addition of 0.20 mol of HCl to this solution? (HF, Ka = 7.2 ́ 10-4)?

pH= 2.74

Calculate the pH of a solution that's 0.65M in NaF and 0.75M in HF. (HF, Ka = 7.2 ́ 10-4)?

pH= 3.07

Consider a solution initially containing 0.400 mol fluoride anion and 0.300 mol of hydrogen fluoride (HF). What is the pH after addition of 70.0 mL of 0.600M HCl to this solution? (HF, Ka = 7.2 ́ 10-4)?

pH= 3.15

Calculate the pH of a solution originally containing 0.20 mol of cyanic acid HCNO following addition of 80 mL of 1.00 M NaOH. (Ka of HCNO = 3.5 x 10-4). The initial volume of the cyanic acid solution was 920 mL, so the final combined volume at the end is 1.0 L. a) 3.28b) 3.39c) 3.46d) 3.64e) none of the above

pH= 3.28

Calculate the pH of a solution that's 0.65M in NaNO2 and 0.40M in HNO2. (NaNO2, Ka = 4.0 ́ 10-4)?

pH= 3.60

26. A buffer system is set up with [HA] = 2[A-]. If pKa = 5.5, what is the pH of the buffer? a. 5.2 d. 3.5 b. 5.8 e. 7.0 c. 7.5

pH= 5.2

If you start with 80.0 mL of 0.40 M HNO3, calculate the pH following addition of 40.0 mL of 0.80 M KOH. a) 3.4b) 7.0c) 8.2d) 11.6e) none of the above

pH= 7

A 25.0 mL solution of quinine was titrated with 1.00 M hydrochloric acid, HCl. It was found that the solution originally contained 0.125 moles of quinine. What was the pH of the solution after 50.00 mL of the HCl solution were added? Quinine is monobasic with pKb = 5.10.

pH= 9.08

Consider a solution initially containing 0.500 mol ammonia (NH3) and 0.300 mol of ammonium ion (NH4+). What is the pH after addition of 40 mL of 0.800M NaOH to this solution? (NH4+, Ka = 5.6 ́ 10-10)?

pH= 9.39

Calculate the pH of a solution that is 0.30 M in ammonia (NH3) and 0.20 M in ammonium chloride (NH4Cl, Ka = 5.62 ́ 10-10).

pH= 9.43

Consider a solution initially containing 0.50 mol ammonia (NH3) and 0.30 mol of ammonium ion (NH4+). What is the pH after addition of 0.20 mol of HCl to this solution? (NH4+, Ka = 5.6 ́ 10-10)?

pH=9.028

The pKa of a weak acid was determined by measuring the pH of a solution containing the weak acid at 0.40 M and its conjugate base at 0.20 M. The measured pH was 9.8. What is the pKa of the weak acid? a. 10.1 d. 10.4 b. 9.8 e. None of the above c. 9.5

pKa= 10.1

The pKa of a weak acid was determined by measuring the pH of a solution containing the weak acid at 0.40 M and its conjugate base at 0.60 M. The measured pH was 7.8. What is the pKa of the weak acid? a. 8.0 d. 7.0 b. 7.8 e. 7.4 c. 7.6

pKa= 7.6

The pKa of a weak acid was determined by measuring the pH of a solution containing the weak acid at 0.30 M and its conjugate base at 0.30 M. The measured pH was 8.0. What is the pKa of the weak acid? a. 8.0 d. 7.0 b. 7.8 e. 7.4 c. 7.6

pKa= 8.0

Phenylephrine(PE,seethestructurebelow)isanasaldecongestantandistheactiveingredientinSudafed,which contains phenylephrine hydrochloride (PEHCl). This conjugate acid of phenylephrine (PEH+) has a pKa = 5.5. At a physiological pH of 7.4. what is the ratio of concentrations, [PE]/[PEH+]? a. 6.7 d. 79 b. 0.01 e. 21 c. 0.14

rato = 1:79

Whensodiumchlorideisaddedtoasaturatedsolutionoflead(II)chloride,someofthelead(II)chlorideprecipitates. This results from what is called the common ion effect. d. a solubility anomaly. selective precipitation. e. deionization. c. supersaturation.

the common ion effect.

Inatitrationofmonoproticacidsandbases,thereisalargechangeinpH a. at the point where pH = pKa of the acid. b. when the volume of acid is exactly equal to the volume of base. c. when the concentration of acid is exactly equal to the concentration of base. d. when the number of moles of acid is exactly equal to the number of moles of base. e. at the point where pH = pKb of the base.

when the number of moles of acid is exactly equal to the number of moles of base.