Lesson test: Buffers and titrations

1.[2p]
A buffer contains $0.090$ mol dm⁻³ acetic acid and $0.110$ mol dm⁻³ acetate, with $p K_{a} = 4.76$ . What is its pH?

CorrectNot quite: 4.85

2.[2p]
Why does diluting a buffer tenfold barely change its pH?

The Henderson-Hasselbalch equation depends on the ratio of the two species, which dilution does not change

Correct

The buffer generates more acid as it is diluted

The answer is: The Henderson-Hasselbalch equation depends on the ratio of the two species, which dilution does not change

Water has no effect on equilibria

The answer is: The Henderson-Hasselbalch equation depends on the ratio of the two species, which dilution does not change

The equilibrium constant changes to compensate

The answer is: The Henderson-Hasselbalch equation depends on the ratio of the two species, which dilution does not change

3.[3p]
$25.00$ mL of $0.1000$ mol dm⁻³ acetic acid ( $p K_{a} = 4.76$ ) is titrated with $0.1000$ mol dm⁻³ NaOH. What is the pH after $12.50$ mL?

CorrectNot quite: 4.76

4.[3p]
For that same titration, what is the pH at the equivalence point, given $K_{b} = 5.71 \times 10^{- 10}$ for acetate and a concentration there of $0.0500$ mol dm⁻³?

CorrectNot quite: 8.73

5.[1p]
The equivalence point of a titration is always at pH 7.

True

The answer is: False

False

Correct

6.[3p]
Methyl orange changes colour between pH $3.1$ and $4.4$ . Why is it the wrong indicator for acetic acid titrated with sodium hydroxide?

Its range lies in the buffer region, far below the vertical jump of that curve

Correct

It is not a weak acid

The answer is: Its range lies in the buffer region, far below the vertical jump of that curve

It reacts with acetate

The answer is: Its range lies in the buffer region, far below the vertical jump of that curve

Its range is too wide to read

The answer is: Its range lies in the buffer region, far below the vertical jump of that curve

7.[2p]
How is a $p K_{a}$ read straight off a titration curve?

It is the pH at the half equivalence point

Correct

It is the pH at the equivalence point

The answer is: It is the pH at the half equivalence point

It is the pH at the start

The answer is: It is the pH at the half equivalence point

It is the volume at the equivalence point

The answer is: It is the pH at the half equivalence point

8.[2p]
Carbonic acid has $p K_{a 1} = 6.35$ and $p K_{a 2} = 10.33$ . What is the approximate pH of a sodium hydrogencarbonate solution?

CorrectNot quite: 8.34

9.[3p]
Which raise the buffer capacity of a solution?

Select all that apply

Increasing the total concentration of the conjugate pair

Correct

Setting the ratio of acid to base near one

Correct

Choosing an acid whose $p K_{a}$ is close to the target pH

Correct

Diluting the solution tenfold

The answer is: Increasing the total concentration of the conjugate pair, Setting the ratio of acid to base near one, Choosing an acid whose $\mathrm{p}K_a$ is close to the target pH

1.[2p] A buffer contains 0.090 mol dm⁻³ acetic acid and 0.110 mol dm⁻³ acetate, with pKa=4.76. What is its pH?

2.[2p] Why does diluting a buffer tenfold barely change its pH?

3.[3p] 25.00 mL of 0.1000 mol dm⁻³ acetic acid (pKa=4.76) is titrated with 0.1000 mol dm⁻³ NaOH. What is the pH after 12.50 mL?

4.[3p] For that same titration, what is the pH at the equivalence point, given Kb=5.71×10-10 for acetate and a concentration there of 0.0500 mol dm⁻³?

5.[1p] The equivalence point of a titration is always at pH 7.

6.[3p] Methyl orange changes colour between pH 3.1 and 4.4. Why is it the wrong indicator for acetic acid titrated with sodium hydroxide?

7.[2p] How is a pKa read straight off a titration curve?

8.[2p] Carbonic acid has pKa1=6.35 and pKa2=10.33. What is the approximate pH of a sodium hydrogencarbonate solution?

9.[3p] Which raise the buffer capacity of a solution?

1.[2p]
A buffer contains $0.090$ mol dm⁻³ acetic acid and $0.110$ mol dm⁻³ acetate, with $p K_{a} = 4.76$ . What is its pH?

2.[2p]
Why does diluting a buffer tenfold barely change its pH?

3.[3p]
$25.00$ mL of $0.1000$ mol dm⁻³ acetic acid ( $p K_{a} = 4.76$ ) is titrated with $0.1000$ mol dm⁻³ NaOH. What is the pH after $12.50$ mL?

4.[3p]
For that same titration, what is the pH at the equivalence point, given $K_{b} = 5.71 \times 10^{- 10}$ for acetate and a concentration there of $0.0500$ mol dm⁻³?

5.[1p]
The equivalence point of a titration is always at pH 7.

6.[3p]
Methyl orange changes colour between pH $3.1$ and $4.4$ . Why is it the wrong indicator for acetic acid titrated with sodium hydroxide?

7.[2p]
How is a $p K_{a}$ read straight off a titration curve?

8.[2p]
Carbonic acid has $p K_{a 1} = 6.35$ and $p K_{a 2} = 10.33$ . What is the approximate pH of a sodium hydrogencarbonate solution?

9.[3p]
Which raise the buffer capacity of a solution?