sodium thiosulphate

• Measuring the rate of a chemical reaction

  1. Prepare sodium thiosulfate and hydrochloric acid solutions

  2. Mix the solutions and observe the reaction

  3. Measure the time for the solution to become cloudy and obscure a cross drawn on paper

  4. Repeat the experiment with different concentrations of sodium thiosulfate

  5. Plot a graph of concentration vs reaction time
• Reaction between sodium thiosulfate and hydrochloric acid

  Produces an insoluble precipitate of sulfur, causing the solution to become cloudy and yellow
• Experimental procedure


  1. Measure 50 cm³ of sodium thiosulfate solution

  2. Measure 10 cm³ of hydrochloric acid

  3. Mix the solutions and start timer

  4. Observe the solution and stop timer when cross is obscured
• Increasing the concentration of sodium thiosulfate

  Decreases the reaction time
• The line of best fit on the graph of concentration vs reaction time is a curve, not a straight line
• Plotting 1/time would give a measure of the reaction rate, as rate decreases as time increases