Chemistry - 8 Rates and Equilibrium - Required Practical 5: Rate of Reaction

Aims:

  • investigate how changes in concentration affect the rates of reaction by measuring gas volume and change in colour or turbidity

Risk Assessment:

  • acid is an irritant and could damage the eyes

Safety:

  • wear safety goggles

Equipment:

  • conical flask

  • rubber bung (opt.)

  • delivery tube (opt.)

  • gas syringe (opt.)

  • stopwatch

  • 40 g/cm³ sodium thiosulfate solution

  • 1.0 M and 1.5 M hydrochloric acid solution

  • 3cm lengths of magnesium ribbon

  • printed black cross

  • measuring cylinders

Control variables:

Method 1: Volume of Gas

  • temperature of surroundings

  • size of magnesium ribbon piece

  • volume of hydrochloric acid

Method 2: Disappearing Cross

  • temperature of surroundings

  • total volume of liquid

  • size and colour of cross

  • concentration of original sodium thiosulfate solution

  • volume of hydrochloric acid

  • concentration of hydrochloric acid

Independent variable:

Method 1: Volume of Gas

  • concentration of hydrochloric acid

Method 2: Disappearing Cross

  • concentration of sodium thiosulfate solution

Dependent variable:

Method 1: Volume of Gas

  • rate of production of hydrogen

Method 2: Disappearing Cross

  • time taken for cross to no longer be visible

Method:

Method 1: Volume of Gas

  1. Using the measuring cylinder, measure 50 cm³ of 1.0 M hydrochloric acid into a conical flask

  2. Add a 3 cm strip of magnesium ribbon to the acid and quickly fit the flask with a rubber bung attached to a delivery tube or gas syringe. Start the stopwatch

  3. Every 10 seconds, record the volume of gas produced until no more gas is produced

  4. Repeat steps 1-3 using the 1.5 M hydrochloric acid solution

Method 2: Disappearing Cross

  1. Using a measuring cylinder, measure 10 cm³ sodium thiosulfate solution into a conical flask. Dilute with enough water to bring the total liquid to 50 cm³ (here, 40 cm³)

  2. Place the conical flask on top of the printed black cross

  3. Using a measuring cylinder, measure out 10 cm³ dilute hydrochloric acid. Add the acid to the conical flask, swirl gently and immediately start the stopwatch

  4. Look down into the conical flask, at the black cross. When it can no longer be seen, stop the stopwatch

  5. Repeat steps 1-4, using different volumes of sodium thiosulfate in step 1 (20 cm³, 30 cm³, 40 cm³)

  6. Repeat steps 1-5 again and calculate a mean time for each concentration

Calculations/graphing:

Method 1: Volume of Gas

  • plot a graph of time against gas volume, plotting two curves - one of 1.0 M hydrochloric acid and one for 1.5 M

Method 2: Disappearing Cross

  • plot a graph of sodium thiosulfate concentration against time taken