Elements of the sea

Question 1

Procedure for iodine thiosulfate titration:

Answer 1

• Use a volumetric pipette to transfer 25.0cm3 of bleach solution to a
  conical flask
• Add an excess of a dilute acid and potassium iodide solution (these can be
  measured with a measuring cylinder as they are in excess)
• Add sodium thiosulfate of a known concentration from a burette
• When the iodine in the conical flask has become a pale straw colour,
  add a few drops of starch solution. A blue/black complex will form
• Continue to add thiosulfate from the burette until the colour of the
  starch/iodine complex disappears
• Repeat the procedure until you have 2 concordant results (+/- 0.1
  cm3).
• Mean titre is the average of the 2 concordant results

Question 2

the risks associated with the storage and transport of chlorine

Answer 2

Risk: Toxic gas
Minimise risk of leakage during transportation by preparing on site wherever
possible
Transported as a pressurised gas (pressurised to liquid)
High risk of leak –
* Tanks have valves to release some chlorine if the pressure becomes too
high.
* Better to release a small amount of chlorine to the atmosphere
than to risk a catastrophic explosion
* Tanks must be completely dry:
* Cl2 reacts with water to form corrosive acids
* These acids would damage the tank and cause risk of leakage