To ensure that all KHCO3 reacts in an experiment, an excess of the other reactant (typically an acid) is used. This ensures that all of the KHCO3 is consumed, and that the reaction goes to completion. The exact amount of excess acid required will depend on the specific reaction being performed.

For example, in a reaction between KHCO3 and HCl, the following equation shows that 1 mole of KHCO3 reacts with 1 mole of HCl:

KHCO3 + HCl → KCl + H2O + CO2

If we want to ensure that all of the KHCO3 reacts, we can use a 10% excess of HCl. This means that we would use 1.1 moles of HCl for every 1 mole of KHCO3.

This excess of acid will ensure that all of the KHCO3 reacts, and that the reaction goes to completion.