RP5 - Rate of Reaction

Question 1

What is the aim of this experiment?

Answer 1

• Investigate how changes in concentration affect the rates of reactions by both measuring the volume of a gas produced and monitoring a change in colour or turbidity (how cloudy a mixture is).

Question 2

Describe how you would investigate the rate of reaction using volume of gas produced

Answer 2

1. Measure 50 cm3 of 1.0 M hydrochloric acid using one of the measuring cylinders. Pour
   the acid into the 100 cm3 conical flask.
2. Set up the apparatus as shown in one of the diagrams below.
3. Add a 3 cm strip of magnesium ribbon to the flask and quickly place the bung back into
   the flask. At the same time, start the stopwatch.
4. Record the volume of hydrogen gas given off every 10 seconds. Stop when no more gas
   is given off.
5. Repeat steps 1-4 using 1.5 M hydrochloric acid
6. Plot a graph of ‘volume of gas produced’ (y-axis) against ‘time’ (x-axis) . Draw two
   curves, one for each concentration of acid.

Question 3

Describe how you would investigate the rate of reaction using colour change or turbidity

Answer 3

1. Measure 10 cm3 sodium thiosulfate solution into the conical flask.
2. Dilute the solution by adding 40 cm3
   water into the conical flask making the concentration
   8 g/cm3
3. Put the conical flask on the black cross.
4. Measure 10 cm3 of dilute hydrochloric acid.
5. Add the acid to the flask. Then quickly at the same time, swirl the flask gently and start
   the stopwatch.
6. Look down through the top of the flask. Stop the clock when you can no longer see the cross and record the time taken.
7. Repeat steps 1‒6 , using different volumes of sodium thiosulfate and water - 20 cm3
   sodium thiosulphate solution + 30 cm3 water, 30 cm3 sodium thiosulphate solution + 20
   cm3 water, 40 cm3
   sodium thiosulphate + 10 cm3 water).
   This will change the concentration of sodium thiosulfate.
8. Repeat steps 1-7 twice more.
9. Calculate the mean time for each of the sodium thiosulfate concentrations.

Question 4

What are the three ways of measuring the rate of a reaction?

Answer 4

• Observe how quickly a precipitate forms
• Measure the change in mass
• Measure the volume of gas given off

Question 5

Why is the precipitate rate experiment not very reliable?

Answer 5

• Subjective - people might disagree over the exact point she the mark disappears or the solution changes colour