💧 Percent Water in a Hydrate Calculator
Enter the mass of a hydrate before and after heating to drive off the water, and find out what percent of its mass was water.
What is a hydrate?
A hydrate is an ionic compound that has water molecules trapped within its crystal structure, written as part of its formula (for example, CuSO4·5H2O). Heating a hydrate drives off this water of crystallization, leaving behind the anhydrous (water-free) salt.
How this calculator works
This calculator uses the classic experimental approach: weigh the hydrate sample, heat it until the mass stops changing, then weigh the remaining anhydrous salt. The difference between the two masses is the mass of water that was driven off. Dividing that by the original hydrate mass and multiplying by 100 gives the percent water by mass.
Percent water = (mass of hydrate − mass of anhydrous salt) ÷ mass of hydrate × 100
Common sources of error in this experiment include incomplete heating (not all water removed) or overheating (decomposing the anhydrous salt itself), both of which can skew the result. This tool is for general chemistry education purposes.