Required practical 5 - Measure the rate of reaction by an initial rate method and a continuous monitoring method.

What is initial rate?

rate at the start of the reaction where it is fastest

What is continous rate?

measuring the change in concentration of a reactant or product over time (or measuring volume of gas released) as the reaction progresses.

How can you calculate initial rate?

Taking the gradient of a Continuous monitoring conc vs time graph and time = zero or clock reactions.

What is a common clock reaction?

Iodine clock - hydrogen peroxide reacts with iodide ions to form iodine. Iodine then reacts with thiosulfate ions. When excess I2 remains in the solution, it turns into a blue black colour.

How can you find the order with this reaction?

Repeating the experiment several times, varying the concentration of a reactant.

Describe the method of this reaction.

Put each of the chemicals in seperate burrettes. Measure out the required volumes of pottasium iodide, sodium thiosulfate, starch and water into a small conical flask. Measure the hydrogen perioxide from the test tube into the conical flask and immediately start the timer. Stop the timer until the first hint of black/blue colour appears.

How do you find the rate of a continous monitoring method?

Find the gradient. The reaction is the fastest where the gadient is the steepest.

What experiment and apparatus is usually used to demonstrate continuous monitoring method?

Mg + HCl and gas syringe.

What happens to the rate when one of the reactants is in a large excess?

If the concentration of one of the reactants is kept at a large excess, than that reactant will appear not to affect rate as its concentration stays virtually constant and does not affect rate.

What are the different ways to measure the rate of reaction?

Change in volume of a gas

Change of mass

Titrating samples of reaction mixture

Colorimetry

Change in electrical conductivity

Optical activity.