Practical 3

• Outline, a method, to investigate how changing the temperature affects the rate of the reaction

  > Measure out 10 cm3 of sodium thiosulfate solution using a measuring cylinder and transfer into a 100 cm3 conical flask

  > Measure out 10 cm3 of hydrochloric acid solution using a measuring cylinder and transfer into a separate 100 cm3 conical flask

  > Place the two conical flasks into a water bath and record the temperature (i.e. 55 ºC)

  > Place a cross marked on a paper below the conical flask with sodium thiosulfate
• Outline, a method, to investigate how changing the temperature affects the rate of the reaction pt 2

  > Immediately start the timer and record the time taken for the cross to disappear

  > Repeat the experiment using the same volume and concentration of hydrochloric acid and sodium thiosulfate but change the temperature of the water bath (45 ºC, 35 ºC, 25 ºC and room temperature)

  > Calculate rate for each experiment using rate = 1/time

  > Plot a graph of rate (y axis) against temperature (x axis)
• State what causes the cross marked under the reaction vessel to disappear.

  The precipitate of sulfur
• State the effect of increasing the temperature on the time taken for the precipitate of sulfur to form. Explain your answer.

   > As temperature increases, the time taken for precipitate to form decreases

  > More particles have an energy equal to or greater than the activation energy

  > Therefore, there are more successful collisions per unit time
• Why is the reaction mixture put in a stop bath containing saturated sodium carbonate solution

  The sodium carbonate neutralises the hydrochloric acid which stops the reaction. This prevents toxic SO2 gas from being produced