ZIMSEC O Level Combined Science Notes: Experiment: Demonstrate the effect of surface area on the rate of a reaction

Materials: magnesium ribbon, magnesium powder, marble chips (another form of calcium carbonate), powdered calcium carbonate, 250cm3 beakers, dilute hydrochloric acid, spatula, splint

Method a

  1. Into two beakers pour an equal volume of dilute hydrochloric acid about 20cm3
  2. Add a small spatula load of magnesium powder to one beaker an at the same time a small piece of magnesium ribbon to the other
  3. Put a lighted splint into the top of each beaker

Observations and results

  • The magnesium powder reacts quickly with the acid and dissolves in the acid at a more rapid rate than the magnesium ribbon
  • Hydrogen is produced and it burns with a popping sound
  • \text{magnesium+hydrochloric acid}\rightarrow\text{magnesium chloride+hydrogen}

Method b

  1. Pour two equal measures into two beakers
  2. Add a small spatula of powdered to calcium carbonate to one beaker containing acid
  3. At the same time add one or two marble to the other beaker

Observations and results

  • Bubbles start to form as a gas is given out by the reactions
  • The reaction with the powdered calcium carbonate finishes first
  • Carbon dioxide is evolved
  • \text{calcium carbonate+hydrochloric acid}\rightarrow\text{calcium chloride+carbon dioxide+water}


  • The smaller the particles involved the faster the rate of the equation
  • The larger the particle size the slower the rate of reaction
  • Crushing or breaking down the solids into powder speeds the rate of reaction
  • This is because the surface area is increased increasing the amount of particles that collide with each other at one given moment in the solution

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