Chapter 17 Homework Flashcards Preview

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Flashcards in Chapter 17 Homework Deck (20)
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1
Q

The three intermediate reactions and the final reaction of acetic acid and ammonia are shown below.
Reaction 2: CH3COOH(aq) + H2O(l) <==> CH3OO-(aq) + H3O+(aq) (Ka = 1.810^-5)
Reaction 3: NH3(aq) + H2O(l) <==> NH4+(aq) + OH-(aq) (Kb = 1.8
10^-5)
Reaction 4: H3O+(aq) + OH-(aq) <==> 2H2O(l) (Ka = 1/Kw = 1/(1*10^-14))
What is the expression and value for KFinal?

A
KFinal = Ka Kb (1 / Kw );
KFinal = 3.2 × 10^4
2
Q

The following reaction represents a buffer system, which responds to the addition of a base or an acid.

CH3COOH(aq) + H2O(l) <==> CH3OO-(aq) + H3O+(aq)

Which statement about this reaction is not correct?

A

The weak acid acts as a proton (H3O+ ) acceptor; the H3O+ ions come from the addition of the strong acid.

3
Q

Suppose that you want to prepare an acidic buffer solution. You add 0.93 M Na2HPO4 to 1.23 M KH2PO4. If Ka (for H2PO4− ) = 6.2 × 10^−8, what is the pH of this buffer solution?

A

7.09

4
Q

Suppose that you have 1.00 liters of a solution of 1.25 M HCOOH and 0.83 M HCOO−. To the solution you add 0.20 mol HCl. What is the first event that will occur?

A

HCl will dissociate to its component ions, H + and Cl −. The HCOO− will react with H + (or H3O+ ) ions to form HCOOH

5
Q

What is the pH difference between a 1.00 L buffer solution (Solution A) of 1.25 M HCOOH and 0.920 M HCOO− and a 1.00 L buffer solution (Solution B) of 2.75 M HCOOH and 0.920 M of HCOO−? when 0.10 moles of HCl is added to both buffer solutions? The Ka = 1.77 × 10−4

A

0.325

6
Q

Which characteristic defines the main difference between a basic buffer system and an acidic buffer system?

A

A basic buffer system is a solution that can maintain a basic pH as more acid or base is added.

7
Q

Suppose that you have a 75 mL solution of 0.200 M HCl that is being titrated with 0.125 M NaOH. At the point indicated by the arrow, 49 mL of NaOH have been added. What is the pH of the solution at this point?

A

1.14

8
Q

Which point on the titration curve for a weak acid shows the point at which we have half of the original amount of weak acid left?

A

B

9
Q

Look at Point D in the titration curve for a weak acid.

CH3COOH(aq) + OH-(aq) <==> Ch3COO-(aq) + H2O(l)

Which statement about the reaction at Point D is not true?

A

The pH at Point D, the equivalence point, is 7.0

10
Q

Which statement about the deprotonations of a diprotic acid is not correct?

A

The value of Ka for the first deprotonation event with a diprotic acid is less than the Ka value for the second deprotonation event.

11
Q

Pb2+ (2.0 × 10−8 moles) is added to a 1 L solution of chromate, CrO42−.

Pb2+(aq) + CrO42-(aq) <==> PbCrO4(s)

(where Ksp = 2.8 × 10−13 )
at which point precipitation begins to occur. What was the concentration of chromate ion in the solution?

A

1.4 × 10^−5

12
Q

What is the solubility of aluminum hydroxide,
Al(OH)3, if Ksp for Al(OH)3 is 3.0 × 10−34?
Al(OH)3(s) <==> Al3+(aq) + 3OH-(aq)

A

1.8 × 10^−9 M

13
Q

The dissociation reaction for CuBr is

What is the solubility of CuBr in a 0.05 M HBr (strong) acid solution? The Ksp for the dissociation of CuBr(s) is 4.2 × 10−8.

A

8.4 × 10^−7

14
Q

Consider the reaction of formic acid and sodium hydroxide.
HCOOH(aq) + NaOH(aq) <==> Na(HCOO)(aq) + H2O(l)
The acid constant, Ka, for formic acid is 1.8*10^-4. From this, calculate the equilibrium constant for the above reaction

A

1.8 × 10^10

15
Q

Which statement about the reaction below is not correct?

HA(aq) <==> H+(aq) + A-(aq)

A

A decrease in [H + ] will cause an increase in [HA].

16
Q

What is the solubility of CaF in 0.08 M NaF solution? Ksp = 3.9 × 10−11 and the dissociation reaction for CaF2 is
CaF2(s) <==> Ca2+(aq) + 2F-(aq)

A

6.1 × 10^−9

17
Q

Which statement about phenolphthalein is not correct?

A

Phenolphthalein indicator works because there is a protonation event that occurs between the central carbon atom and an oxygen atom.

18
Q

Adding Ag+ to a 0.10 M chromate CrO42− solution, eventually yields silver chromate, Ag2CrO4(s).

Ag2CrO4(s) <==> 2Ag+(aq) + CrO42-(aq)

(where Ksp = 9.0 × 10−12 )

Which statement about this reaction is not correct?

A

Initially, when Ag+ is first added, you have a nonprecipitate solution of Ag+ and Ag2CrO4 in equilibrium with each other.

19
Q

Suppose that you wanted to prepare a buffer solution with a pH of 2.07. Which of the following tells you which acid-base pair to use and how you must alter that acid-base pair to get as close as possible to the pH?

A

Acid-base pair #1; You would have to increase the [A− ].

20
Q

Suppose that you wanted to prepare a acetate ion / acetic acid buffer solution with a pH of 5.01. What is the value of [A− ] / [HA] for the correct buffer solution for this event? The Ka is 1.8 × 10^−5

A

1.86

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