Study Hack Lab

RP 2Chemistry

Neutralisation

Write-up template

Name
Date
Course: GCSE Chemistry
Board and specification: AQA GCSE Chemistry (8462), 4.4.2.5Apparatus and techniques: AT 1, AT 8
Class and teacher

Aim

Find the volume of dilute sulfuric acid that exactly neutralises 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide solution, then (Higher tier) the acid’s concentration in mol/dm³ and g/dm³.

Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up

A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. Layout v1, practical v4. Original material; not affiliated with AQA, which has not reviewed it.

1 Plan and risk assessment

Acid neutralises alkali: H⁺ ions react with OH⁻ ions to make water. The indicator changes colour at the end point, when the alkali has just been neutralised. From the volume of acid needed (the titre) and the known concentration of the alkali, you can work out the concentration of the acid: moles = concentration × volume in dm³.

2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)

Variables

Independent (you change)
Dependent (you measure)
Control (you keep the same)

Prediction

Methyl orange is added to the sodium hydroxide in the flask. You add acid from the burette. What colour change shows the end point?

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O. If the sulfuric acid were 0.050 mol/dm³, what volume would neutralise 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide?

How will you know when you have done enough titrations?

Risk assessment

Hazard	Harm it could cause	Control

2 Apparatus

Safety goggles Protect your eyes from the alkali and the acid.
50 cm³ burette (resolution 0.05 cm³) Adds the acid and measures how much was added.
Clamp stand with a burette clamp Holds the burette vertical over the flask.
Small funnel For filling the burette.
25.0 cm³ pipette and pipette filler (resolution ±0.06 cm³) Measures exactly 25.0 cm³ of alkali.
250 cm³ conical flask Holds the alkali; can be swirled without spilling.
White tile Makes the colour change easy to see.
Sodium hydroxide solution, 0.100 mol/dm³ The alkali of known concentration.
Dilute sulfuric acid (concentration unknown) The acid you are finding the concentration of.
Indicators in dropping bottles Methyl orange, phenolphthalein and universal indicator.
Labelled beakers and a wash bottle of distilled water For the acid, the alkali, waste and rinsing.

3 Method

Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.

4 Results

The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.

Titrations of 25.0 cm³ of sodium hydroxide solution with sulfuric acid · Record each burette reading to 2 decimal places (to the nearest 0.05 cm³). Titre = final reading − initial reading. If you retake a titration, the table shows the retake’s final reading; the colour cell still records what you saw in the first flask, whose reading is no longer used.

Titration	Initial burette reading in cm³	Final burette reading in cm³	Titre in cm³	Colour at the end
Rough
1
2
3
Mean (concordant)

Anomalies

Ring any anomalous result. Say what probably went wrong and whether you repeated it.

5 Graph

This practical has no graph: summarise your results in a sentence.

6 Analysis

Mean titre
mean = sum of the concordant titres ÷ number of them
Answer
Moles of sodium hydroxide (Higher tier)
moles = concentration × volume in dm³
Answer
Moles of sulfuric acid (Higher tier)
2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)
Answer
Concentration of the acid (Higher tier)
concentration = moles ÷ volume in dm³
Answer
In g/dm³ (Higher tier)
mass concentration = concentration × Mr (Mr of H₂SO₄ = 98)
Answer

7 Conclusion and evaluation

Conclusion

Conclusion: what do your results show? Use your own numbers.

Sources of error

For each, say whether it is systematic or random, and how it affected your results.

Judging the end point (the colour change)

Reading the burette (parallax and the 0.05 cm³ resolution)

Burette rinsed with water, not the acid

Pipette rinsed with water, not the alkali

Conical flask rinsed with the alkali

Measuring the alkali with a measuring cylinder

Improvement

How could you improve the method? Say why it would help.

8 Make safe and clear up

Run the acid left in the burette into a beaker, rinse the burette with water and clamp it upside down with the tap open
Rinse the pipette with water and put it back in its rack
Pour the neutralised solutions from the flasks down the sink with plenty of water
Wipe up any drips with a damp cloth, then take off your goggles and wash your hands