When doing the nitrate test, why can't I use 5 ml of water, one spoon of Reagent 1 and 3 drops of Reagent 2 ? Wouldn't that result in twice as many measurements ?
If you use 5 ml instead of the 10 ml of sample liquid, this would yield distorted results for two reasons.
For one, the powder for the reduction of NO₃ doesn't dissolve completely so that it forms a thin layer of sediment which causes difficulties when reading the results with too little water. Tapping the cuvette on the side several times helps by causing the powder to be deposited on the side.
Secondly, attention must be paid to the drop size of reagent 2, as the first drop from the drop dispenser can turn out to be smaller in individual cases, especially when the bottle is not held in a fully vertical position. This may also lead to incorrect measuring results. Therefore, it is advisable to use 10 ml in order to ensure accurate test results. Please make sure to really shake hard for exactly one minute in order for the colour to develop properly.