colorimetry

• when is colorimetry used?

  when one of the reactants/products is a coloured solution.
• what is a colorimeter used for?

  to measure the intensity in the solution's colour. It uses a light source to shine white light through a filter into the reaction mixture. Some white light frequencies are absorbed by the sample and other white light frequencies are transmitted through the sample.
• what is the progress of the reaction followed by?

  monitoring the changes in the solution's colour intensity over time during the formation of a coloured product/removal of a coloured reactant.
• what is a light sensitive cell used for?

  a light sensitive cell detects the frequencies of the light transmitted through or absorbed by the sample. This is then displayed on the colorimeter. The readings are measured at specific time intervals throughout the reaction and this can be used to produce a graph of absorption or transmission against time.
• how can we determine the concentration of the reactant/product at each time interval?

  the absorption/transmission values can be compared to a calibration curve to work out concentration of reactant/product at each time interval.
• what can the results be used for?

  to draw a graph of concentration over time.