Introduction  (Page 3/3)

$CaC{O}_3+2HCl\to CaC{l}_2+H_{2}O+C{O}_2$

Aim:

To determine the effect of the surface area of reactants on the rate of the reaction.

Apparatus:

2 g marble chips, 2 g powdered marble, hydrochloric acid, beaker, two test tubes.

Method:

1. Prepare a solution of hydrochloric acid in the beaker by adding 2 cm ${}^3$ of the concentrated solution to 20 cm ${}^3$ of water.
2. Place the marble chips and powdered marble into separate test tubes.
3. Add 10 cm ${}^3$ of the dilute hydrochloric acid to each of the test tubes and observe the rate at which carbon dioxide gas is produced.

Results:

• Which reaction proceeds the fastest?
• Can you explain this?

Conclusions:

The reaction with powdered marble is the fastest. The smaller the pieces of marble are, the greater the surface area for the reaction to take place. The greater the surface area of the reactants, the faster the reaction rate will be.

Experiment : reactant concentration and reaction rate.

Aim:

To determine the effect of reactant concentration on reaction rate.

Apparatus:

Concentrated hydrochloric acid (HCl), magnesium ribbon, two beakers, two test tubes, measuring cylinder.

Method:

1. Prepare a solution of dilute hydrochloric acid in one of the beakers by diluting 1 part concentrated acid with 10 parts water. For example, if you measure 1 cm ${}^3$ of concentrated acid in a measuring cylinder and pour it into a beaker, you will need to add 10 cm ${}^3$ of water to the beaker as well. In the same way, if you pour 2 cm ${}^3$ of concentrated acid into a beaker, you will need to add 20 cm ${}^3$ of water. Both of these are 1:10 solutions. Pour 10 cm ${}^3$ of the 1:10 solution into a test tube and mark it 'A'. Remember to add the acid to the water , and not the other way around.
2. Prepare a second solution of dilute hydrochloric acid by diluting 1 part concentrated acid with 20 parts water. Pour 10cm ${}^3$ of this 1:20 solution into a second test tube and mark it 'B'.
3. Take two pieces of magnesium ribbon of the same length . At the same time, put one piece of magnesium ribbon into test tube A and the other into test tube B, and observe closely what happens.

The equation for the reaction is:

$2HCl+Mg\to MgC{l}_2+H_2$

Results:

• Which of the two solutions is more concentrated, the 1:10 or 1:20 hydrochloric acid solution?
• In which of the test tubes is the reaction the fastest? Suggest a reason for this.
• How can you measure the rate of this reaction?
• What is the gas that is given off?
• Why was it important that the same length of magnesium ribbon was used for each reaction?

Conclusions:

The 1:10 solution is more concentrated and this reaction therefore proceeds faster. The greater the concentration of the reactants, the faster the rate of the reaction. The rate of the reaction can be measured by the rate at which hydrogen gas is produced.

Group work : the effect of temperature on reaction rate

1. In groups of 4-6, design an experiment that will help you to see the effect of temperature on the reaction time of 2 cm of magnesium ribbon and 20 ml of vinegar. During your group discussion, you should think about the following:
   • What equipment will you need?
   • How will you conduct the experiment to make sure that you are able to compare the results for different temperatures?
   • How will you record your results?
   • What safety precautions will you need to take when you carry out this experiment?
2. Present your experiment ideas to the rest of the class, and give them a chance to comment on what you have done.
3. Once you have received feedback, carry out the experiment and record your results.
4. What can you conclude from your experiment?