2 Colourimetric tests
This method involves adding reagents to form a coloured compound with the analyte, then either measuring the intensity of that colour by eye or using a portable photometer.
As we are carrying out some chemistry to enable us to measure an analyte either visually or instrumentally, the very fact that we are doing this in the field may throw up an additional problem. You will be aware that the rate of a chemical reaction increases with increasing temperature, so the temperature in the immediately surrounding area when the test is carried out must also be taken into account.
For example, a reaction leading to a colour change would be significantly slower on a cold winter's day than in the heat of summer.
Considering what's going on at the molecular level, why does the rate of a chemical reaction increase with increasing temperature?
A greater proportion of reactants encounter each other with sufficient energy to overcome the energy barrier for the reaction.