This question is about acids and alkalis.
Dilute hydrochloric acid is a strong acid.
Explain why an acid can be described as both strong and dilute. 2 marks]
ANSWER
A concentrated acid is one in which many acid molecules are dissolved in a set volume of solution, while a dilute acid will have very few molecules per unit volume.
A 1.0 x 10–3 mol/dm3 solution of hydrochloric acid has a pH of 3.0.
What is the pH of a 1.0 x 10–5 mol/dm3 solution of hydrochloric acid?
[1 mark]
ANSWER
pH will be 5
A student titrated 25.0 cm3 portions of dilute sulfuric acid with a 0.105 mol/dm3 sodium hydroxide solution.
Table 4 shows the student’s results.
Table 4
The equation for the reaction is:
Calculate the concentration of the sulfuric acid in mol/dm3.
Use only the student’s concordant results.
Concordant results are those within 0.10 cm3 of each other.
[5 marks]
ANSWER
Keeping in view the concordant results, so we choose values of titrations 3, 4 & 5;
By seeing the given equation, the reacting reaction of NaOH: H2SO4 = 2:1
Therefore,
Explain why the student should use a pipette to measure the dilute sulfuric acid and a burette to measure the sodium hydroxide solution.
[2 marks]
ANSWER
Pipette measures a fixed volume accurately but burette measures variable volume.
Calculate the mass of sodium hydroxide in 30.0 cm3 of a 0.105 mol/dm3 solution.
Relative formula mass (Mr): NaOH = 40
[2 marks]
ANSWER
