Applications Safety Reagents & Buffers Ammonium Beer's Law Biological membranes Chlorine (Free) Chlorine (Total) Crystal Violet Enzymes Ethanol Fats/Oils Glucose Halogenoalkanes Hill Reaction Iodination of propanone Iodine Clock Reaction Iron Manganese in Steel Nitrate Nitrite Phosphate Population growth Protein Thiosulphate/HCl Vitamin C

Reaction of sodium thiosulphate with acid

This is a well-known reaction found in most chemistry books and often carried out at GCSE level.

Sodium thiosulphate reacts with acid to produce sulphur which is deposited in the solution causing it to become opaque.

    Na2S2O3 + 2HCl → 2NaCl + S + SO2 + H2O

The colorimeter can be used to measure the rate of this reaction since the increasing opacity scatters the light passing through.

Safety

There are no hazards associated with the basic investigations described here.
At 0.1M the concentration of hydrochloric acid used in the examples given is well below that requiring a hazard warning label.

Good laboratory practices should be observed.

Go back to the top of the page
Video
Go back to the top of the page
Results
    thiosulphate

    thiosulphate graph

Go back to the top of the page
Methods

This investigation can be carried out with small volumes and low concentrations of the reactants.

  • put 1.5cm3 of dilute hydrochloric acid into a cuvette
  • add 1.5cm3 of sodium thiosulphate
  • read absorbance (best with the blue LED).

pdf Click to download a pdf file containing much of the information about this topic.

Go back to the top of the page

Copyright 2012 Mystrica Ltd.