Calculating the Results for Using the Iodine Clock Method to Find the Order of a Reaction Activity E

1
Calculating the Results for Using the Iodine
Clock Method to Find the Order of a Reaction
(Activity EP6.4)
2

• The following series of steps is required to
  complete the calculations
• Calculating the concentration of I- in the 5
  reaction mixtures
• Mixture 1 I- Volume of KI x KI
• Total volume of mixture
• 5.0 x 0.1
• 10
• 0.5 mol dm-3
• For the other mixtures substitute the appropriate
  volumes into the above equation

3
Reactant in excess (part c)

• The number of mol of I- in mixture 5 is
  calculated as follows
• Concentration volume of KI x KI
  1 x 1.0 0.1 mol dm-3
• Total volume of mixture 10
• The S2O82- in mixture 5 is calculated as
  follows
• Concentration volume of K2S2O8 x
  K2S2O8 2 x 0.04
• Total volume of mixture 10
• 8 x 10-3 mol dm-3
• The calculation shows that I- is in excess.
• Why is mixture 5 used?

4
Total amount of iodine produced (part d)

• This is calculated from the reaction between
  peroxodisulphate(VI) ions and iodide ions. The
  reaction for this is
• S2O82- (aq) 2I- (aq) 2SO42- (aq) I2 (aq)
• The total moles of iodine produced is calculated
  as
• K2S2O8 x Total volume of
  mixture
• 
  1000
• 8 x 10-3 x 10
• 1000
• 8 x 10-5 moles I2 can be produced

5
The amount in moles of thiosulphate ions added to
each mixture (part e i)

• This is calculated as
• Na2S2O3 x volume added
• 1000
• 0.01 X 2
• 1000
• 2 x 10-5 moles

6
The amount of iodine used up by thiosulphate
ions (part e ii)

• The reaction is
• 2S2O32- (aq) I2 (aq) S4O62- (aq) 2I-
  (aq)
• In the reaction 2 moles thiosulphate ions react
  with 1 mole of iodine.
• The reaction is 21 and the moles of iodine used
  up is calculated to be
• 1 x 10-5 moles

7
The percentage of the reaction studied (part e
iii)

• This is calculated as follows
• Reaction studied Moles of iodine used x
  100
• Moles of iodine made
• 1 x 10-5 x 100
• 8 x 10-5
• 12.5

8
Calculating the initial rate

• The can be calculated for each mixture as
  follows
• Rate The number of moles of iodine used
• Time taken for colour to appear (T)
• Or
• 1 x 10-5
• T

9
Tabulating the results