Experiments

The experiment’s aim

The experiment’s aim is to design an experiment set-up that proves how a fine grind, temperature and stirring affect the reaction rate.

The experiment can be carried out using different sugars, for example. Remember that sugar dissolution is different from ion compound dissolution. You can review the phenomenon on a molecular level with this Java simulation.

Experiment design and execution

Decide which substances and pieces of equipment you need in the experiment. For example:

• Beakers
• ...
• ...

Plan how you will carry out the experiment. Write a description about how the experiment will progress, and draw illustrative images. Carry out the experiment and write down all observations as thoroughly as possible.

Reporting

Write a report on what took place based on the assignment instructions. The report should present the work progress, results and results-based discussion on the factors that affect the reaction rate.

Simulation: sugar and salt solution

Theory

Iodate and sulphite ions react with each other in the following way:

${\text{IO}}_3^{-<!--\; -\; -->}\text{(aq)}+{\text{3 SO}}_3^{2-<!--\; -\; -->}\text{(aq)}\to <!--\; \to \; -->{\text{I}}^{-<!--\; -\; -->}\text{(ag)}+{\text{3 SO}}_4^{2-<!--\; -\; -->}\text{(ag)}$

The reaction is easy to observe, because the substance colours change clearly. The reaction continues as follows:

${\text{5 I}}^{-<!--\; -\; -->}\text{(ag)}+{\text{IO}}_3^{-<!--\; -\; -->}\text{(ag)}+{\text{6 H}}^{+}\text{(ag)}\to <!--\; \to \; -->{\text{3 I}}_2\text{(ag)}+{\text{3 H}}_2\text{O (l)}$

${\text{I}}_2\text{(ag)}+\text{starch}\to <!--\; \to \; -->\text{blue colour}$

The iodine colours the starch solution a strong shade of blue. The reason is that the iodine molecules place themselves inside the spiral-like starch molecules.

The experiment’s aim

We can experimentally prove that concentration affects the rate at which iodate and sulphite ions react with each other. The colour change can be used to determine differences in the reaction rate. The name iodine clock comes from how precise the reaction is.

Solution preparation

Equipment and reagents:

• 2 beakers
• 2 normal 100 ml beakers
• 2 tall 250 ml beakers
• starch
• potassium iodate, KIO₃
• sodium sulphate, Na₂SO₃
• 2 M of sulphuric acid solution
• distilled water

To make the starch solution, mix 1 g of starch (potato or rice starch) into 10 ml of cold water. Pour the mixture into 90 ml of hot water. When mixed well in hot water, the starch becomes a colloidal solution (compare with thickening custard in the kitchen).

To make solution A, dissolve 0.5 g of potassium iodate into 300 ml of water. Check that all potassium iodate has dissolved into the water (slowly dissolving salt).

To make solution B, add 0.3 g of sodium sulphite, 8 ml of sulphuric acid solution and 12 ml of starch solution into 280 ml of water.

Place 100 ml of solution A into a beaker. This makes solution A1. Then, take another beaker, and place 50 ml of solution A and 50 ml of distilled water into it. This makes solution A2. Take two 250 ml beakers, and pour 100 ml of solution B in both of them. This makes solutions B1 and B2.

Instructions

The potassium iodate concentration is higher in solution A1 than in solution A2. The sodium sulphite concentration, on the other hand, is the same in both B solutions. Simultaneously pour solution A1 into solution B1 and solution A2 into solution B2.

Results and discussion

Which of the reactions is faster? Why?

The experiment studies changes in reaction rates using the principles of colorimetry. In other words, the solution concentration is determined with a change in colour. The studied reaction’s original colour disappears as the reaction progresses.

${\text{2 MnO}}_4^{-<!--\; -\; -->}\text{(ag)}+{\text{16 H}}^{+}\text{(ag)}+{\text{5 (COO}}^{-<!--\; -\; -->}{\text{)}}_2\text{(ag)}\to <!--\; \to \; -->{\text{2 Mn}}^{2+}+{\text{8 H}}_2\text{O(l)}+{\text{10 CO}}_2\text{(g)}$

Excitation

The experiment studies the decomposition reactions of hydrogen peroxide. Find out what the reaction equation is to learn what happens chemically.

Equipment and substances

• hydrogen peroxide (30 %)
• potassium iodide
• dishwashing detergent
• test tube and test tube rack
• saucer to place below the test tube rack
• safety gloves, safety glasses and lab coat

Work safety

Hydrogen peroxide is corrosive, so the teacher will give instructions on how to handle it.

Instructions

Place the test tube rack on top of the saucer. Measure 3 ml of hydrogen peroxide into a test tube. Observe the situation for a moment. Are there reactions occurring in the test tube? Add a few drops of dishwashing detergent. Then, add one spoon-tip of potassium iodide.

Results and discussion

• What happens in the test tube?
• Which substance functioned as a catalyst in the reaction?
• What was the dishwasher detergent’s purpose in the reaction?
• Why did the reaction container heat up as the reaction progressed?