Rates of Reaction

Rates of Reaction Coursework

Aim:

To find out how different concentrations of sodium thiosulphate (Na S2 O3) affects the speed of its reaction with Hydrochloric acid (HCL).

Introduction

When Sodium Thiosulphate and Hydrochloric acid react they produce a cloudy precipitate. Both of the chemicals are clear solutions and they react together to form a yellow precipitate of sulphur, the equation for this reaction is:

Na2 S2 O3 + HCL, H2 O + NaCL + SO2 + S

Sodium Thiosulphate + Hydrochloric acid, Water + Sodium chloride + Sulphur dioxide

Because the solution turns cloudy we observe the rate of reaction by putting a black cross under the flask and watch and time the reaction until the cross disappears. Factors that can affect this experiment are temperature, concentration and time. I will change the concentration of the Sodium Thiosulphate because this is easily varied.

Preliminary work

For my preliminary work I tried doing the experiment with 40cm3 of Hydrochloric acid and I used the same concentration of Sodium Thiosulphate. I was given 0.1m of Sodium Thiosulphate and required to change the concentration I had. I had to dilute the solution and make different concentrations on my own. I added the Hydrochloric acid to the Sodium Thiosulphate and watched it until the solution turned cloudy and I couldn’t see the black cross at the bottom of the flask anymore. I timed how long it took for that to happen.

Apparatus

Method

1. Measure 30cm3 of Hydrochloric acid

2. Measure 30cm3 of Sodium Thiosulphate and out and ‘x’ mat under the flask.

3. Add the 30cm3 of Hydrochloric acid to a flask and then add the Sodium Thiosulphate and start the stop watch.

4. Keep watching the solution until it goes cloudy enough that you can’t see the black cross on the mat anymore, which you placed under the flask, then stop the stop watch.

5. Keep repeating and adding 5cm3 less Sodium Thiosulphate and 5cm3 more water each time to make different concentrations.

6. The concentrations I will use are :

• 0.1

• 0.08

• 0.06

• 0.05

• 0.03

• 0.01

To make it a fair test I will do the experiment three times. I will keep the same flask, same black cross, same measuring cylinders, same volume and concentration of Hydrochloric acid and I am just going to change the concentration of the Sodium Thiosulphate. The concentrations I will use are: 30cm3 of Hydrochloric acid and for the Sodium Thiosulphate I will keep repeating but adding 5cm3 less Sodium Thiosulphate and 5cm3 more water each time to make my different concentrations.

Main experiment

Prediction

My prediction is that the lower the concentration the slower the reaction

Hypothesis

I think that the lower the concentration the slower the reaction will be, I think this because I know that before two particles can react they have to meet. In a low concentration there will be very few particles and they will be spread. This means that the number of reactions will be less because fewer particles will meet. When there is a high concentration there are more particles and so there is more chance of them coming into contact with other particles.

Concentrated solution dilute solution

If the two molecules collide and go off as new substances that means that it is a successful reaction. It produces new substances. A chemical reaction can only occur if the reacting particles collide with enough energy (activation energy)