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CHEM 212 > Midterm 2 (CH 17-19) > Flashcards

Midterm 2 (CH 17-19) Flashcards

1
Q

When a chemical system is at equilibrium:

A
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2
Q

Which of the following has an effect on the magnitude of the equilibrium constant?
A)Removing products as they are formed
B)Adding more of a reactant
C)Adding a Catalyst
D)Increasing the pressure, in a gas-gas reaction
E)Change in temperature

A

E)Change in temperature

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14
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15
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16
Q

Which of the following is a strong acid?
A)H2CO3
B)H2SO3
C)H2SO4
D)H3PO3
E)CH3COOH

A

C)H2SO4

Strong acids include the hydrohalic acids (HCl, HBr, HI) and oxoacids in which the number of oxygen atoms exceeds ionizable protons by two or more

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17
Q

Which of the following acids has the lowest pH?

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

pure water

A

HBO (lowest pKA = strongest acid = highest Ka)

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18
Q

What is the pH of a 0.20 M HCl solution?

A

B) 0.70

pH=-log(H3O+)
pH= -log (.2) because HCl fully dissociates in aqueous environments and therefore [H3O+] = .2

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19
Q

What is the pH of a 0.0035 M KOH solution?

A

E)11.54

pOH=-log[OH-] pH + pOH = 14
pOH=-log[.0035]= 2.46

14-2.46=pH
pH=11.54

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20
Q

What is the [OH−] for a solution at 25°C that has [H3O+] = 2.35 × 10−3 M?

A

C)4.26 x 10^-12

[H3O+] x [OH-] = 1x10^-14

[OH-]= (1x10^-14)/(2.35x10^-3)

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21
Q

What is the [H3O+] for a solution at 25°C that has pOH = 5.640?

A

C)4.37x10^-9

pH+pOH=14
14-5.640=8.36

10^-pH = [H3O+]
10^-8.36=[H3O+]

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22
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23
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24
Q

Butyric acid is responsible for the odor in rancid butter. A solution of 0.25 M butyric acid has a pH of 2.71. What is the Ka for the acid?

A

D)1.5x10^-5

CH3CH2CH2COOH = butyric acid

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25
Q

What is the value of Kb for the cyanide anion, CN−? Ka(HCN) = 6.2 × 10−10

A

B)1.6 × 10−5

Kw=Ka x Kb Kw=1x10^-14

(1x10^-14)/(6.2x10^-10) = 1.6x10^-5

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26
Q

Which of the following aqueous liquids is the most acidic?

A
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27
Q

A solution is prepared by adding 0.10 mol of sodium fluoride, NaF, to 1.00 L of water. Which statement about the solution is correct?

A

A) The solution is basic

NaF + H2O -> Na+ F- Solution will be basic as there are no acidic ions to balance the basicity.

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28
Q

A solution is prepared by adding 0.10 mol of iron(III) nitrate, Fe(NO3)3, to 1.00 L of water. Which statement about the solution is correct?

A

C)The solution is acidic

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29
Q

Which of the following is considered a Lewis acid?

A

Lewis acid = lone pair acceptor. Must have an atom that has an empty orbital to accept electrons.

B)BCl3 Boron has empty p orbitals and can accept the lone pairs

30
Q

Which one of the following is a Lewis acid but not a Brønsted-Lowry acid?

A

A)Fe3+

Lewis Acid is a lone pair acceptor whereas Brønsted-Lowry acid donates a proton in aqueous solution and must have a proton in the formula. Fe3+ is a Lewis Acid but doesn’t have a proton to donate and therefore is not a Brønsted-Lowry Acid

31
Q

Which of the following aqueous mixtures would be a buffer system?

A

D)H3PO4, H2PO4−

Buffer system consists of an acid and its conjugate base

32
Q

Which of the following has the highest buffer capacity?

A

0.50 M H2PO4−/0.50 M HPO42−

-Buffer capacity is best at 1:1 ratio of acid and conjugate base
-0.5M + 0.5M

33
Q

A solution is prepared by adding 500 mL of 0.3 M NaClO to 500 mL of 0.4 M HClO. What is the pH of this solution?

A
34
Q

What is the pH of a buffer that consists of 0.45 M CH3COOH and 0.35 M CH3COONa?
Ka = 1.8 × 10−5

A
35
Q

What is the pH of a buffer that consists of 0.20 M NaH2PO4 and 0.40 M Na2HPO4?
For NaH2PO4, Ka = 6.2 × 10−8

A

pH=7.51

36
Q

You need to use KH2PO4 and K2HPO4 to prepare a buffer with a pH of 7.45. Which of the following ratios of [base]/[acid] is required? For phosphoric acid, (H3PO4), Ka2 = 6.2 × 10−8.

A
37
Q

At the equivalence point in an acid-base titration:

A

The moles of acid = moles of base

ensure that it is in stoichiometric ratio

38
Q

When a strong acid is titrated with a strong base, the pH at the equivalence point:

A

is equal to 7.0

39
Q

When a weak acid is titrated with a strong base, the pH at the equivalence point:

A

is >7.0

40
Q

When a strong acid is titrated with a weak base, the pH at the equivalence point

A

is < 7.0

41
Q

Describe the titration curve of a weak acid and weak base

A

Equivalence point depends on relative concentrations of each.

42
Q

Describe the titration curve of a polyprotic acid

A

Multiple equivalence associated with the different Ka values for each acidic proton

43
Q
A
44
Q

The indicator propyl red has Ka = 3.3 × 10−6. What would be the approximate pH range over which it would change color?

A

pH of an indicator = +/- pKa
pKa=-log(3.3x10^-6)= 5.48
pH= 4.5-6.5

45
Q

A 50.0-mL sample of 0.50 M HCl is titrated with 0.50 M NaOH. What is the pH of the solution after 28.0 mL of NaOH have been added to the acid?

A
46
Q

Write the ion product expression for calcium phosphate, Ca3(PO4)2.

A
47
Q

The solubility of silver chromate is 0.0287 g/1.0 L of solution. What is the Ksp for Ag2CrO4?

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CHEM 212 (6 decks)

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