Concentration varies directly with the rate of reaction

Concentration varies directly with the rate of reaction

ZIMSEC O Level Combined Science Notes: Experiment: Investigating the effects of concentration on marble chips

Aim: To investigate the effect of concentration on the reaction between marble chips and hydrochloric acid

Materials : conical flask/glass jam jars, measuring cylinder, stop clock/watch with seconds/stop watch app, direct reading balance, dilute hydrochloric acid, cotton wool, marble chips


  1. Place 40cm3 of hydrochloric acid in an conical flask
  2. Add 20g of marble chips
  3. Place a loose plug of cotton wool in the neck of the flask to prevent acid spray escaping
  4. Place the whole apparatus on a balance and find its mass
  5. Note the time as soon as the mass is known
  6. Note the mass every half minute for about 10 minutes
  7. Put the results in a table
  8. Plot a graph showing the loss of mass on the vertical/y-axis and time one the x-axis
  9. Repeat the experiment with 20g of the same marble chip size and 20cm3  of the acid made up to 40 using distilled water
  10. Plot the results on the same graph
  11. Compare the slopes of the two graphs

Observation and results

  • The reaction using a higher concentration of hydrochloric acid is faster
  • The resulting graph has a steeper slope showing a quick reduction in mass
  • The second reaction takes longer
  • The resulting graph has a gentler slope


  • The higher the concentration of the acid the faster the reaction
  • Reactions can be sped up by using reagents with a higher concentration

To access more topics go to the Combined Science Notes page.