Study Hack Lab

RP 5Chemistry

Rates of reaction

Write-up template

Name
Date
Course: GCSE Chemistry
Board and specification: AQA GCSE Chemistry (8462), 4.6.1.2AQA GCSE Combined Science: Trilogy (8464), 5.6.1.2Apparatus and techniques: AT 1, AT 3, AT 5, AT 6
Class and teacher

Aim

Investigate how the concentration of a reactant affects the rate of a reaction: by the volume of hydrogen given off by magnesium and acid, and by the time for sulfur to hide a cross.

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 v2. Original material; not affiliated with AQA, which has not reviewed it.

1 Plan and risk assessment

Particles react only when they collide with enough energy. A more concentrated solution has more particles in the same volume, so collisions are more frequent and the rate is higher. Mean rate = quantity of product ÷ time; the rate at one moment is the gradient of a tangent to the curve.

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) and Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO₂(g) + H₂O(l)

Variables

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

Prediction

As the concentration of sodium thiosulfate goes up, what happens to the time for the cross to disappear?

If you plot rate (1 ÷ time) against concentration, what will the graph look like?

You react the same length of magnesium ribbon with 2.0 mol/dm³ acid instead of 1.0 mol/dm³ (the acid is in excess). How much hydrogen do you get in the end?

Risk assessment

Hazard	Harm it could cause	Control

2 Apparatus

100 cm³ gas syringe (resolution 1 cm³) Collects and measures the hydrogen.
Bung with delivery tube Seals the flask and leads the gas to the syringe.
Clamp stand, boss and clamp Holds the syringe level and safe.
100 cm³ conical flask (gas) Where the magnesium reacts with the acid.
Magnesium ribbon (4.0 cm pieces) and emery paper The metal; emery paper cleans off the oxide.
Hydrochloric acid, 1.0 and 2.0 mol/dm³ Reacts with the magnesium and with the thiosulfate.
Sodium thiosulfate solution, 40 g/dm³ Reacts with acid to make the sulfur that hides the cross.
Distilled water (wash bottle) Dilutes the thiosulfate; rinses the flask.
Measuring cylinders: 10 cm³ and 100 cm³ (resolution 0.2 cm³ and 1 cm³) Measure the acid, the thiosulfate and the water.
100 cm³ conical flask (cross) Where the sulfur forms.
Printed black cross on white paper What you watch disappear.
Stopclock (resolution 1 s (m:ss display)) Times each run.
Thermometer (resolution 1 °C) Room temperature, a control variable.
Safety glasses Protect your eyes from the acid.

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.

Method 1: volume of hydrogen · 4.0 cm of magnesium ribbon in 50 cm³ of hydrochloric acid. Read the gas syringe every 10 s.

Time in s	Volume of hydrogen with 1.0 mol/dm³ acid in cm³	Volume of hydrogen with 2.0 mol/dm³ acid in cm³
0
10
20
30
40
50
60
70
80
90

Method 2: the disappearing cross · Each run: thiosulfate and water (50 cm³ in all) on the cross, then 10 cm³ of 2.0 mol/dm³ hydrochloric acid. The whole set of five, three times.

Volume of sodium thiosulfate in cm³	Volume of water in cm³	Concentration of sodium thiosulfate in g/dm³	Time, trial 1 in s	Time, trial 2 in s	Time, trial 3 in s	Mean time in s
10
20
30
40
50

Anomalies

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

5 Graph

Volume of hydrogen against time · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.

Mean time against concentration · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.

Rate (1 ÷ time) against concentration · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.

6 Analysis

Mean rate, 1.0 mol/dm³ acid
mean rate of reaction = quantity of product formed ÷ time taken
Answer
Mean rate, 2.0 mol/dm³ acid
mean rate of reaction = quantity of product formed ÷ time taken
Answer
Rate of reaction at 30 s
Answer
Rate as 1 ÷ time
rate = 1 ÷ mean time
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 moment the cross can no longer be seen

Reaction time starting and stopping the stopclock

Starting the stopclock after pouring and swirling

The room warming up during the lesson

Hydrogen escaping before the bung goes in

A leaking bung or tube

A sticking syringe plunger

Oxide coating on the magnesium

Sulfur left in the flask (not rinsed between runs)

Improvement

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

8 Make safe and clear up

Pour the last cloudy mixture down the sink with plenty of water, straight away (sulfur dioxide)
Rinse the flasks and brush out the yellow sulfur
Take the bung out, push the syringe plunger back in and unclamp the syringe
Rinse the magnesium flask and wipe up any acid spills
Put the acid and thiosulfate bottles back and wash your hands