Required Practical 7 - Measuring Rate of Reaction

In what 2 ways can rate of reaction be calculated from the initial rate?

The gradient of a continuous time-conc graph at t = 0

Clock reactions where time to reach a fixed conc is measured

Briefly describe how a clock reaction works.

When a reagent is used up in the first of 2 reactions, it results in a sudden colour change due to the second reaction

How can order of reaction with respect to a certain reactant be measured using a clock reaction?

Repeat the experiment several times, varying the concentration of the reactant and measuring the time for each

How is initial rate represented for a clock reaction?

1/t

Describe a method to carry out an iodine clock reaction.

1. Add each chemical to a separate burette 

2. Measure out the required volume of potassium iodide, sodium thiosulfate, water and starch into the conical flask

3. Measure the hydrogen peroxide into a test tube

4. Add the hydrogen peroxide into the conical flask and start the timer

5. Stop the timer when the mixture turns blue-black 

Describe how to work out the order of reaction graphically for a clock reaction.

Plot a graph of log(rate) against log(conc I^-)

The gradient of the graph is equal to the rate of reaction

What is represented by the gradient of conc vs time using the continuous rate method?

The rate of reaction 

What is represented by the gradient of 0 on a continuous rate graph?

The reaction has stopped

What must be the case for a continuous rate method where volume of gas is measured? 

One of the reaction’s products must be a gas 

Describe a method for monitoring the volume of gas produced in the continuous rate method. 

1. Measure 50cm³ of the 1.0mol dm^-3 HCl into the conical flask 

2. Set up the apparatus 

3. Add 0.2g magnesium to the acid and place the bung onto the flask and start the times

4. Record the volume of hydrogen produced every 15 seconds for 3 minutes 

How can human error be reduced in the iodine clock reaction?

Use a colorimeter to measure the colour change instead of estimating