Acids               Quiz #8           Buffers and Indicators                      

 

1.         Consider the following acid solutions:

            I. H2CO3          II. HClO4         III. HF

 

            Which of the above acids would form a buffer solution when its conjugate base is             added?

 

            A.        I only

            B.        II only

            C.        I and III only

            D.        I, II, and III only

 

2.         Consider the following base indicator:

                        HInd ⇄ H+ + Ind-     

            When the indicator is added to different solutions, the following data are      obtained:

 

Solution

1.0 M HCl

1.0 M HAl

1.0 M HA2

Colour

Yellow

Blue

Yellow

 

 

 

           

            The acids HAl, HA2, and HInd listed in the order of decreasing acid strength is

            A.        HA2, HInd, HAl

            B.        HInd, HAl, HA2

            C.        HA2, HAl, HInd

            D.        HAl, HInd, HA2

 

3.         Which of the following compounds, when added to a solution of ammonium

            nitrate, will result in the formation of a buffer solution?

            A.        Ammonia

            B.        Nitric acid

            C.        Sodium nitrate

            D.        Ammonium chloride

 

4.         Which of the following represents a buffer equilibrium?

            A.        HI + H2O ⇄ H3O+ + I-

            B.        HCl + H2O ⇄ H3O + Cl-

            C.        HCN + H2O ⇄ H3O+ + CN-

            D.        HClO4 + H2O ⇄ H3O + ClO4-      

 

5.         Consider the following equilibrium:

                        HF(aq) + H2O(l) ⇄ H3O+(aq) + F-(aq)

            The above system will behave as a buffer when the [F-] is approximately equal to

            A.        Ka

            B.        [HF]

            C.        [H2O]

            D.        [H3O+]

 

6.         A basic buffer solution can be prepared by mixing equal numbers of moles of

            A.        NH4Cl and HCl

            B.        NaCl and NaOH

            C.        Na2CO3 and NaHCO3

            D.        NaCH3COO and CH3COOH

 

7.         Which of the following would be used to prepare an acidic buffer solution?

            A.        HF and H3O+

            B.        NaHS and H2S

            C.        NH3 and NH4Cl

            D.        HCl and NaCl

 

8.         HCN(aq)  +  H2O           ⇌        H3O+(aq)            +          CN-(aq)

            1.0 M                                       0.0001 M                     0.0001 M

            Why is the solution above not considered to be a true buffer solution?

            A.        excessive [HCN]

            B.        excessive [H3O+]

            C.        insufficient [CN-]

            D.        insufficient [HCN]

 

9.         What could be added to 1.0 L of this solution in order for it to behave as a true buffer?

            A.        1.0 mol HCl

            B.        1.0 mol HCN

            C.        1.0 mol H3O+

            D.        1.0 mol NaCN

 

10.       Which of the following could typically be used to prepare a buffer solution?

            A.        NaHS and H2S

            B.        HS and Na2S

            C.        HNO3 and NaNO3

            D.        HNO3 and NaNO2

 

11.       What happens to the pH of a buffer solution if a small amount of acid is added?

            A.        The pH remains constant.

            B.        The pH increases slightly.

            C.        The pH decreases slightly.

            D.        The pH decreases significantly.

12.       Consider the following buffer equilibrium:

            HF       +    H2O     ⇌     H3O+   +   F-

            What concentration would limit the buffering action if acid were added?

            A.        [F-]

            B.        [HF]

            C.        [H2O]

            D.        [H3O+]

 

13.       Consider the following buffer equilibrium:

            HF       +    H2O     ⇌     H3O+   +   F-

            What concentration would limit the buffering action if base were added?

            A.        [F-]

            B.        [HF]

            C.        [H2O]

            D.        [H3O+]

 

14.       Which term does the following statement best describe?  A mixture of a weak

            acid and its conjugate base, each with distinguishing colours.           

            A.        buffer

            B.        titration

            C.        indicator

            D.        conjugate

 

15.       The HC2O4-(aq) ion will act as

            A.        a base since Ka  >  Kb

            B.        a base since Ka  <  Kb

            C.        an acid since Ka  >  Kb

            D.        an acid since Ka  <  Kb

 

16.       What do a chemical indicator and a buffer solution typically both contain?

            A.        a strong acid and its conjugate acid

            B.        a strong acid and its conjugate base

            C.        a weak acid and its conjugate acid

            D.        a weak acid and its conjugate base

 

17.       What is the approximate pH and Ka at the transition point for phenol red?

           

                        pH                   Ka

            A.        6.0                   6.3  x  10-7

            B.        7.3                   3.1  x  10-14

            C.        7.3                   5.0  x  10-8

            D.        8.0                   1.0  x  10-8

 

18.       Which of the following acids could not be present in a buffer solution?

            A.        HF

            B.        HNO2

            C.        H2SO3

            D.        HCl

 

19.       The indicator phenol red will be red in which of the following solutions?

            A.        1.0 M HF

            B.        1.0 M HBr

            C.        1.0 M NH4Cl

            D.        1.0 M NaHCO3

 

20.       Which of the following chemical indicators has a Ka  =  1.6  x  10-4 ?

            A.        methyl orange

            B.        phenolphthalein

            C.        thymolphthalein

            D.        bromcresol green

 

21.       Which of the following chemical indicators has a Ka  =  7.9  x  10-10 ?

            A.        methyl orange

            B.        phenolphthalein

            C.        thymolphthalein

            D.        bromcresol green

 

22.       What is the Ka for phenolphthalein?

            A.        1  x  10-14

               B.        8  x  10-10

               C.        1  x  109

               D.        1.0  x  10-7

 

23.       What volume of  0.250 M KOH is required to titrate 0.00230 mol of the weak

            acid H2CO4 ?

            A.        1.15 mL

            B.        4.60 mL

            C.        9.20 mL

            D.        18.4 mL

 

24.       What is the net ionic equation for the titration of H3PO4(aq) with Sr(OH)2(aq) ?

            A.        H+(aq)     +     OH- (aq)     ®     H2O(l)

           

            B.        6H+(aq)     +     6OH-(aq)     ®     6H2O(l)

           

            C.        2H3PO4(aq)  +  3Sr2+(aq)  +  6OH-(aq)   ®   Sr3(PO4)2(s)   +    6H2O(l)

           

            D.        6H+(aq)  +   2PO43-(aq) + 3Sr2+(aq) +  6OH- (aq)   ® 3Sr2+ + 2PO43-(aq) +  6H2O(l)

 

25.       Which of the following will have the smallest Ka value?

            A.        HF

            B.        H2CO3

            C.        H3PO4

            D.        CH3COOH

 

26.       Which of the following will have the smallest Kb value?

            A.        IO3-

            B.        NH3

            C.        CN-

            D.        HPO42-

 

27.       What volume of 0.500 M NaOH is required to neutralize 25.0 mL 0.250 M HBr ?

            A.        5.00 mL

            B.        12.5 mL

            C.        20.0 mL

            D.        25.0 mL

 

28.       Which of the following equations correctly represents the reaction of a metallic

            oxide with water?

            A.        K2O   +   H2O   ®   2KOH

            B.        SO3    +   H2O    ®   H2SO4

            C.        Na2O  +  H2O    ®    Na2O2   +   H2

            D.        NaOH   +   HCl   ®   NaCl   +  HOH

 

29.       Which of the following equations describes the dissociation of the salt,

            ammonium chloride, in water?

            A.        NH4Cl(s)   ®   NH4Cl(aq)

            B.        NH4+(aq)   +   Cl-(aq)   ®   NH4Cl(s)

            C.        NH4Cl(s)   ®  NH4+(aq)   +   Cl-(aq)

            D.        NH4+(aq)  +   H2O(l)    ®   H3O+(aq)   +   NH3(aq)

 

30.       Which of the following salt solutions is acidic?

            A.        NaBr

            B.        AlCl3

            C.        Li2CO3

            D.        NaHCO3