Self-assessment
Question 1 of 8
A student has a test tube containing 0.1 mol dm–3 ammmonia solution and another test tube containing 0.1 mol dm–3 sodium hydroxide solution. However, she has mixed up the labels and relies on her pH tests and conductivity results in order to identify the correct samples. Which of the results and conclusions below represents her notes.
A
Tube A: pH 11, conductivity low is NaOH(aq)
Tube B: pH 13, conductivity high is NH3(aq)
B
Tube A: pH 1, conductivity high is NaOH(aq)
Tube B: pH 3, conductivity low is NH3(aq)
C
Tube A: pH 13, conductivity low is NaOH(aq)
Tube B: pH 11, conductivity high is NH3(aq)
D
Tube A: pH 13, conductivity high is NaOH(aq)
Tube B: pH 11, conductivity low is NH3(aq)
Which of the following statements about weak acids are true?
A
Carboxylic acids are the commonest weak acids and they contain the –C(O)OH group
B
Carboxylic acids ionise to a limited extent by the loss of a proton from the carboxyl group.
C
A carboxylic acid ionises more easily if it contains electron withdrawing groups that stabilise the carboxylate ion.
D
H2SO3, H2CO3 and HCN are examples of weak acids.
What is the pH of a 0.02 mol dm-3 solution of nitric acid, and how does the pH of an equimolar solution of ethanoic acid compare?
A
pH 1.7 and the pH of weak acid is higher
B
pH 0.4 and pH of weak acid is higher
C
pH 1.7 and the pH of a weak acid is lower.
D
pH 3.9 and pH of weak acid is lower
Consider 1M HCl(aq), approximately what proportion of the HCl molecules are left undissociated (Ka is around 106)
A
1 in every 1,000,000
B
1 in every 100,000
C
1 in every 10,000
D
1 in every 1000
A weak acid has a Ka of around 1 x 10–6. Roughly estimate what proportion of acid molecules dissociate in a 1M solution?
A
1 in 100
B
1 in 1000
C
1 in 10 000
D
1 in 100 000
A student is looking up the pKa values, for some common organic acids. Using your knowedge of chemical structures, choose which of the following lists the acids in order of increasing strength in your estimation. (Hint: think which one ionises most easily).
A
CCl3COOH, C6H5COOH, HCOOH, CH3COOH
B
CH3COOH, C6H5COOH, HCOOH, CCl3COOH
C
HCOOH, CH3COOH, C6H5COOH, CCl3COOH
D
CH3COOH, HCOOH, CCl3COOH, C6H5COOH,
Calculate the concentration of a solution of propanoic acid that has [H+] = 5.70 x 10-4 mol dm–3. The data book value for the Ka of propanoic acid is 1.3 x 10–5.
A
0.025 mol dm–3
B
5.7 mol dm–3
C
0.0125 mol dm–3
D
3.25 x 10–7 mol dm–3
What might you, the teacher, say to a student who was reluctant to use pKa values and would always ignore them and use Ka values instead?
A
pKa values are numerical values that are most often easier to handle than the corresponding Ka.
B
Never mind what it means. You just need to know when to use a pKa in an exam question.
C
Using a pKa value instead of a Ka value is like using a pH instead of the corresponding concentration that can be a number with many powers of ten.
D
Just learn the equation.