RQP 7: Measuring the rate of a reaction

Question 1

What are the two ways of calculating the initial rate of a reaction

Answer 1

1. Taking the gradient of a continuous monitoring conc vs time graph at time=zero
2. From clock reactions where the time taken to reach a fixed concentration is measured

Question 2

How do you determine the order of reactants experimentally

Answer 2

By doing a series of experiments and differing the concentration of only one reactant whilst keeping the others contant then looking at the effect this has on initial rate to determine its order

Question 3

What can be use as initial rate of a reaction

Answer 3

1/t

Question 4

What is a common reaction that may be asked using the initial rate method

Answer 4

The reaction between hydrogen peroxide and iodide ions

Question 5

Describe how to measure the initial rate of the reaction between hydrogen peroxide and iodide ions in order to determine the order of the reactants

Answer 5

• put each of the chemicals in separate burettes
• In each experiment measure out required volumes of the potassium iodide, sodium thiosulfate, starch and water into a small conical flask from the burettes.
• Measure the hydrogen peroxide into a test tube
• Pour the hydrogen peroxide from the test tube into the conical flask and immediately start the timer. Stir the mixture.
• Time until the first hint of blue/black colour appears
• repeat with diffderent concentrations of potassium iodide
• Do each reaction at the same temperature

Question 6

What is the most common continuous monitoring method used to measure the rate of a reaction

Answer 6

Using a gas syringe

Question 7

Describe how to use a gas syringe to measure the rate of reaction between magnesium and hydrochloric acid

Answer 7

1. Measure 50cm^3 of the 1 moldm^-3 hydrochloric acid and add to a conical flask.
2. Set up the gas syringe in the stand
3. Weigh 0.2g magnesium
4. Add the magensium ribbon to the conical flask, place the bung firmly into the top of the flask and start the timer.
5. Record the volume of hydrogen gas collected every collected every 15 seconds for 3 minutes
6. Plot a graph of volume of gas produced against time