Tuesday 21st (c)

The effect of concentration and the rate of reaction


Aim: To see if changing the concentration of solution A affects the rate of reaction with solution B.


Theory: In the reaction the soluble starch will react, instantly changing the colour of the mixed solutions dark blue. The speed at which he colour change depends on the concentration of solution, which is diluted by water each time.

2x concentration  → 0.5 time


Method: Solution A is mixed using 2g of potassium iodate and 1000ml of water. Solution B is mixed using 2g of soluble starch, 0.4g sodium metabisulphite, 5mol l-1 of sulphuric acid and 1000ml of water. Measure out 160ml of each solution into beakers. With a stopwatch, time how long it takes for the two solutions to react once mixed together. The results are recorded. Repeat process but using 80ml of solution A, 80ml of water and 160ml of solution B. repeat the process again using 40ml of solution A, 120ml of water and 160ml of solution B. the results are recorded in a table.




Solution A(ml) Water(ml) Solution(ml) Time(s) Rate 1/t(s-1)
160 0 160 90 0.01
80 80 160 170 0.005
40 120 160 360 0.002


Conclusion: the lower the concentration of solution A, the longer it takes to react therefore the reaction rate decreases.