METHOD 1:

• INDEPENDENT VARIABLE:

  Volume of SODIUM THIOSULPHATE solution
• DEPENDENT VARIABLE:

  • TIME taken for the CROSS to DISAPPEAR
• CONTROL VARIABLES:

  • Same TEMPERATURE
  • VOLUME/ CONCENTRATION of HYDROCHLORIC acid
• STEP 1:

  • Using a measuring CYLINDER, add 10cm3 of SODIUM THIOSULFATE solution into a CONICAL flask
• STEP 2:

  • Place the FLASK over a PRINTED black CROSS
• STEP 3:

  • Add 10cm3 of HYDROCHLORIC acid, SWIRL flask and start the STOPWATCH
• STEP 4:

  • Look down through the TOP of the FLASK
  • Solution should turn CLOUDY
  • Stop the STOPWATCH when CROSS cannot be seen
• STEP 5:

  • Carry out the experiment again using a LOWER concentration of SODIUM THIOSULFATE
• STEP 6:

  • REPEAT the WHOLE experiment again
  • Calculate a MEAN for each CONCENTRATION
  • Ignore ANOMALOUS results
• PROBLEM:

  • Different PEOPLE, different EYESIGHTS (FASTER / SLOWER idea of the ROR)
  • SOLUTION: Same SIZE of the CROSS should be used