Displacement reactions and reactivity

Introduction

Displacement reactions occur when a more reactive metal is added to a solution of a compound of a less reactive metal. The reactivity series can be used to predict the outcome of these reactions.

This experiment investigates how temperature changes during displacement reactions using temperature sensors and how this can be used to predict the reactivity of the metals used.

Materials

• Computer
• Datalogger
• Temperature sensor
• 150 ml and 250 ml beakers
• 1M copper sulphate solution
• Iron powder
• Magnesium powder
• Zinc powder

Methods

The apparatus was set up as in the photograph below. The temperature was taken over a three-minute period using the graphing application of datalogging software. The experiment was started as soon as the metal was added to the copper sulphate.

Three experiments were carried out:

• A displacement reaction between 50cm³ 1M copper sulphate solution and 3 spatulas of zinc powder.
• A displacement reaction between 50cm³ 1M copper sulphate solution and 3 spatulas of magnesium powder.
• A displacement reaction between 50cm³ 1M copper sulphate solution and 3 spatulas of iron powder.

Results

The data above are available in several different forms, depending on which software you have available and whether you want to carry out extra analysis using the datalogging software.

Formats available

SID file.
CSV file [suitable for using directly as a table in Excel].
ISA file.
ISD file.

More information on using these files can be obtained from Introduction to datalogging.

Conclusions

1. What is the general pattern seen in the graph above for experiments A-C after the two reactants are added together?
2. What word from the following list best describes experiments A-C:
              Neutralisation, endothermic, exothermic, isothermic?
3. Produce an order of reactions for experiments A-C, from the one in which there is the greatest temperature change to one in which there is the least.
4. Identify which reaction is A-D if one of them is the room temperature graph and the other three are the experiments.
5. Explain your answer to question 4.
6. Explain why it is important to look at temperature change instead of optimum temperature to compare the results of the experiments.

Extension questions

1. Write down word equations for all three reactions used in this experiment.
2. Write down symbol equations for all three reactions used in this experiment.
3. Explain what you think would happen when:
        a) Iron sulphate was added to zinc.
        b) Magnesium was added to zinc sulphate.
        c) Copper sulphate was added to silver.

Extension tasks

Investigate what happens to the temperature when different displacement reactions are used, for example:
        a) when lead and tin are added to copper sulphate.
        b) when magnesium, zinc, lead, tin and copper are added to iron sulphate.