Exam 3

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Question #1

A solution containing CaCl2 is mixed with a solution of Li2C2O4 to form a solution that is 2.1 × 10-5 M in calcium ion and 4.75 × 10-5 M in oxalate ion. What will happen once these solutions are mixed forming the concentrations given above? Ksp (CaC2O4) = 2.3 × 10-9.

A Nothing will happen since calcium oxalate is extremely soluble.

B A precipitate will form since Qsp > Ksp for calcium oxalate.

C Nothing will happen since both calcium chloride and lithium oxalate are soluble compounds.

D There is not enough information to determine.

E No precipitant will form since Qsp < Ksp

Question #2

If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.54, which of the following is TRUE?

A It is not possible to make a buffer of this pH from HCHO2 and NaCHO2.

B [HCHO2] = [NaCHO2]

C [HCHO2] < [NaCHO2]

D [HCHO2] > [NaCHO2]

E Does not have enough information to tell

Question #3

Which of the following titrations result in a acidic solution at the equivalence point?

A NaOH titrated with HNO3, HClO3 titrated with NaOH

B HI titrated with NaCH3CO2 , Ba(NO2)2 titrated with HCl

C HBr titrated with Ba(OH)2, NaOH titrated with HNO3

D None of the above

Question #4

To simulate the pH of blood, which is 7.29, an undergraduate researcher in a biology lab produced a buffer solution by dissolving sodium dihydrogen phosphate and disodium hydrogen phosphate together in an aqueous solution. What mole ratio of Na2HPO4/NaH2PO4 did she need to use? Ka2 = 6.2 x 10–8 and Ka3=3.6 x 10–13

A 1.6

B 1

C 0.96

D 1.2

E None of the choices are correct

F 0.9

Question #5

An unknown student takes 25.0 mL sample of an unknown weak base solution with a an unknown concentration and titrates it with H2SO4 solution. At half-equivalence point the pH is 11.20. It takes 16mL of H2SO4 to reach an equivalence point. What would be the concentration of the unknown weak base sample ________ M if the pOH at equivalence point is 8.12.

A 0.654

B 0.935

C 0.452

D 1.069

E 1.211

Question #6

What volume (in mL) of 0.15M NaOH to you have to add to 50.7 mL of 0.15 M acetic acid (CH3CO2H) to prepare a buffer solution with a pH of 5.02? The pKa of acetic acid is 4.74.

A 40.25

B 39.17

C 33.25

D 25.28

E 28.74

Question #7

A 15.0 mL sample of 0.723 M HClO4 is titrated with a 0.135M Ba(OH)2 solution. The H3O+ concentration after the addition of 75.00mL of Ba(OH)2 is ________ M.

A 4.6 × 10-13

B 9.6×10-14

C 2.9 × 10-13

D 1.0 × 10-7

E 2.2 x 10–2 M

Question #8

A 25.0 mL solution of quinine was titrated with 1.00 M Sulfuric acid, H2SO4. It was found that the solution contained 110 mmoles of quinine (a week base). What would be the pOH at equivalence point. Quinine is monobasic with pKb = 5.10.

A 8.9

B 9.62

C 5.1

D None of the choices are correct

E 4.38

F 9.51

Question #9

Which of the following acids has the weakest conjugate base?
0.1 M HBO, pKa = 2.43
0.1 M HA, pKa = 4.55
0.1 M HMO, pKa = 8.23
0.1 M HST, pKa = 11.89

A HMO

B HA

C pure water

D HST

E HBO

Question #10

What is the pH of your best liquid soap made from a fatty acid (HA) that has a pKa value of 4.0? The concentration of the active ingredient for the solution, a fatty acid conjugate base (NaA), is 0.23 M NaA.

A 8.68

B 9.23

C 6.78

D 8.08

E 5.48

Question #11

The conjugate acid of H2PO4 – is __________

A H3O+

B HPO4-2

C H3PO4

D H2PO4

E none of the above

Question #12

Arrange the following 0.10 M aqueous solutions in order of increasing pH (Low pH to high pH): NaOH, HBr, NaCH3CO2, KBr, NH4Br.

A HBr, NH4Br, KBr, NaCH3CO2, NaOH

B NaOH, NaCH3CO2, KBr, NH4Br, HBr

C HBr, KBr, NH4Br, NaCH3CO2, NaOH

D NaOH, NaCH3CO2, NH4Br, KBr, HBr

Question #13

If the pOH of an aqueous H2SO4 solution is 12
Would the pOH of solution in part A increase, decrease or remain the same if the water evaporates on a hot day

A increase

B remain the same if the water evaporates on a hot day

C decrease

Question #14

If the pOH of an aqueous H2SO4 solution is 12
What would be the concentration of H2SO4 ?

A 0.005

B 0.008

C 0.015

D 0.05

Question #15

The acid-dissociation constants of phosphorous acid (H3PO3) are Ka1 = 7.5 × 10-3, Ka2 = 6.2 × 10-8, and Ka3 = 4.2 × 10-13 at 25.0°C. Which dissociation constants would you use to solve for the pH of 0.5M solution of Na3PO3?

A Kb3 and Ka2

B Kb3

C Kb3 and Ka1

D Kb1 and Ka2

E Kb2 and Ka3

F Ka1

Question #16

A BrØnsted-Lowry base is defined as a substance that __________.

A increases Ka when placed in H2O

B acts as a proton acceptor

C acts as a proton donor

D decreases [H+] when placed in H2O

E increases [OH-] when placed in H2O

Question #17

Which one of the following, A–D, is correct?

A K2SO3 is a weaker base than KHSO3.

B Na2HPO4 is a stronger acid than NaH2PO4.

C NaHSO3 is a stronger base than NaHSO4.

D K2CO3 is a weaker base than KHCO3.

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