Design- Rate of Reaction

HYPOTHESIS

It can be predicted that if the concentration of a reactant is increased, the rate of reaction is increased. Thus, at a higher concentration of a reactant, the rate at which the reaction will occur will be higher whereas if the concentration of a reactant is lowered, the rate at which the reaction will occur will be lower i.e. decreased. It can also be predicted that the equilibrium of the reaction will be shifted depending on the increase or decrease in concentrations.

VARIABLES

Dependant Variable

Time taken for yellow Sulphur particles to form which obscures the ‘X’ mark.

Independent Variable

Concentration of reactant (Na2S2O3)

Controlled Variables

1. The volume of acid (HCl) added to the various concentrations of Na2S2O3
2. Room Temperature (to be kept constant
3. Pressure
4. Surface Area
5. Number of stirs

APPARATUS

CHEMICALS

1. 0.15 M Sodium Thiosulphate solution (23.7 g Na2S2O3 dissolved in deionized or distilled water to make one liter of solution)
2. 6 M HCl solution (dilute 500 dm3 concentrated HCl solution to one liter with distilled or deionized water)

EQUIPMENT

1. 0.250 dm3 beakers
2. Stirring rods
3. 0.025 dm3 graduated cylinder
4. Clock (which can measure in seconds)
5. White Paper
6. Black/Dark coloured marker

6. The level of sodium thiosulphate and hydrochloric acid in the beaker
7. The room temperature and pressure (as these are other factors which affect the rate of reaction.)

PROCEDURE

1. Obtain five 0.250 dm3 beakers, about 0.03 dm3 of hydrochloric acid solution, and about 0.080 dm3 of sodium thiosulphate solution. Label the beakers from 1 to 5. Add the amounts of sodium thiosulfate solution and distilled or deionized water to each cup indicated in the following table:

2. Make a table that shows the information in the table above and also includes a column for time (sec) and relative rate (sec-1).
3. Ensure that the fan is switched off and there is no form of external air to ensure a constant temperature and pressure.

4. Make a small "x" on a sheet of white paper with a pencil. Place a beaker containing the sodium thiosulfate solution over this "x." Add 0.005dm3 HCl solution and begin timing the reaction as soon as the acid touches the sodium thiosulfate solution. Stir the reaction mixture at a constant rate throughout the reaction. Ensure that the volume of HCl is the same in all beakers.

5. Stop timing when the "x" under the beaker is no longer visible through the solution. Record this time in your data table.

6. Repeat steps 2-4 for the remaining samples.

7. Make a graph of your data by plotting the time (in sec) for each reaction on the y-axis against the volume (in dm3) of sodium thiosulfate stock solution on the x-axis.

8. Calculate the relative rate of each reaction by taking the reciprocal of each time measurement. Record these results in your data table.

9. Make a second graph by plotting the relative rate of each reaction on the y-axis against the volume of sodium thiosulfate solution on the x-axis.

PRECAUTIONS

1. Concentrated solution of HC1 will burn skin or damage clothing; avoid skin contact with acid.

2. Reactions should be carried out in a hood or well-ventilated room.

3. Some poisonous SO2(g) is produced. Students should be cautioned against leaning over reaction vessel too closely as they observe the "x" under the beaker.

4. Goggles should be worn throughout the experiment.

DATA TABLE