Investigating the effect of changing concentration on the rate of reaction

Research Question:

How does concentration of a reactant affect the rate of reaction in an experiment?

Hypothesis:

I predict that the higher the concentration the faster the rate of reaction in the experiment will be. This is because for substances to react it involves collisions between the particles in the solution, so if the solution has a higher concentration then there will be a greater number of molecules reacting at the same time meaning that there will be more collisions per second (as with more molecules there are greater chances of collision) and so the reaction will occur faster.

Variables:

Independent Variable:  Concentration of the reactant (mols of Hydrochloric Acid)

Dependant Variable: Time taken to react (seconds)

Control Variables: Volume of hydrochloric acid, Volume and concentration of Sodium Thiosulphate, temperature of the room, air pressure in the room, size and shape of beaker

Apparatus:

• Hydrochloric acid (1M, 2M, 3M, 4M, 5M)
• Beakers
• Sodium Thiosulphate
• Conical Flask
• Paper marked with a cross
• Measuring cylinder
• Stop-clock

Method:

1. Collect all the apparatus and set it up as shown in the diagram (except without the reactants)
2. Measure out 25 cm3 of 1M Hydrochloric acid and 10 cm3 of Sodium Thiosulphate using a measuring cylinder
3. Pour the 1M Hydrochloric acid into the flask
4. Pour the sodium thiosulphate into the flask and start the stop-clock immediately
5. Watch the cross on the piece of paper looking down through the flask, and as soon as the cross disappears because the contents of the flask get cloudier, stop the stop-clock
6. Record the time, and repeat the experiment again but with 2M Hydrochloric acid and so on until 5M of Hydrochloric acid is reached
7. Repeat the entire experiment again to obtain a second set of results at every concentration of acid, average the two results and draw a graph