Acids, alkalis and titrations

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Question 2

A student uses the neutralisation method to make a sample of the soluble salt, lithium sulfate.

The equation for the reaction they use is:

2\text{LiOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Li}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)

The student does a titration using these steps to find the ratio of the volumes of reactants needed.

Add $cm325.0\text{ cm}^3$ of lithium hydroxide solution to a conical flask
Add a few drops of phenolphthalein indicator to the conical flask
Add dilute sulfuric acid from a burette until the indicator just changes colour
Repeat the experiment until concordant results are obtained

Which piece of apparatus should the student use to add the lithium hydroxide solution?

[1]

What colour change would the student see when they neutralise the lithium hydroxide solution?

Colour before neutralisation: $\text{_____________}$
Colour after neutralisation: $\text{_____________}$

[1]

The diagram shows the burette readings in one experiment before and after adding the acid.

Burette readings

Use the readings to calculate the volume of acid added, entering all values to the nearest $cm30.05\text{ cm}^3$ .

burette reading after adding acid = $\text{_____________}$ $cm3\text{cm}^3$
burette reading before adding acid = $\text{_____________}$ $cm3\text{cm}^3$
volume of acid added = $\text{_____________}$ $cm3\text{cm}^3$

[3]

The student repeats the experiment and records these results:

	Trial 1	Trial 2	Trial 3	Trial 4
Burette reading after adding acid ( $cm3\text{cm}^3$ )	29.20	28.10	27.45	26.90
Burette reading before adding acid ( $cm3\text{cm}^3$ )	3.10	2.35	1.60	2.10
Volume of acid added ( $cm3\text{cm}^3$ )	26.10	25.75	25.85	24.80
Titration results to be used ( $✓\checkmark$ )

The average (mean) volume of acid added should be calculated using only concordant results (those that differ from each other by $cm30.20\text{ cm}^3$ or less).

Identify the concordant results by stating which trials should be ticked.

[1]

Use your identified results to calculate the average volume of acid added.

[2]

The student uses $cm3500\text{ cm}^3$ of lithium hydroxide solution of concentration $mol/dm30.400\text{ mol/dm}^3$ to prepare a sample of lithium sulfate solution.

Calculate the amount, in moles, of $LiOH\text{LiOH}$ in the lithium hydroxide solution.

[1]

Calculate the amount, in moles, of $H2SO4\text{H}_2\text{SO}_4$ needed to neutralise this amount of $LiOH\text{LiOH}$ .

[1]

Calculate the mass, in grams, of this amount of $H2SO4\text{H}_2\text{SO}_4$ .

[2]

Trial 1

Trial 2

Trial 3

Trial 4

Burette reading after adding acid (

cm3\text{cm}^3

)

29.20

28.10

27.45

26.90

Burette reading before adding acid (

cm3\text{cm}^3

)

3.10

2.35

1.60

2.10

Volume of acid added (

cm3\text{cm}^3

)

26.10

25.75

25.85

24.80

Titration results to be used (

✓\checkmark

)

Acids, alkalis and titrations

Question 2

Acids, alkalis and titrations Questions

Acids, alkalis and titrations

Question 2

Acids, alkalis and titrations Questions