Hydrate formula calculator

How to find the water of hydration

The mass difference supplies the water mass. Convert that mass and the dry-salt mass to moles separately, then divide. A gram ratio would give a different answer because water and salt have different molar masses.

The same grams-to-moles relationship is used twice. Le Moyne College's hydrate analysis describes this water-to-salt ratio method. This page analyzes supplied measurements; it is not a heating procedure.

Worked example: a five-to-one ratio

Take idealized sample masses of 2.49677 g before and 1.59602 g after water loss, with CuSO₄ as the known dry residue. The formula mass used here is 159.602 g/mol.

1. Water lost: 2.49677 − 1.59602 = 0.90075 g.
2. Water: 0.90075 ÷ 18.015 = 0.05 mol.
3. CuSO₄: 1.59602 ÷ 159.602 = 0.01 mol.
4. Ratio: 0.05 ÷ 0.01 = 5 mol water per mol salt.

Those ideal values are consistent with CuSO₄·5H₂O. They were chosen to make the arithmetic transparent, not to imply this precision in an ordinary balance reading. Water is about 36.08% of the starting mass.

Subtract the container once

If your notebook records the container and sample together, select that method and enter the empty-container mass as well. For the example above, a 20 g container gives readings of 22.49677 g and 21.59602 g. The calculator subtracts 20 g from both readings.

The container cancels when finding water loss, but it does not cancel from the dry-salt mass used to find salt moles. Leaving it in the denominator can badly change the ratio. Include the same lid or other weighed pieces in every relevant reading.

Why the calculator does not force a whole number

A result such as 4.97 may suggest comparison with a five-water hydrate, but rounding alone is not evidence for a chemical formula. Check the expected material and the precision and repeatability of the measurements. Some hydrate ratios are fractional when expressed per formula unit, so the app preserves the numerical ratio instead of converting every result to an integer.

If your assignment expects a whole-number coefficient, compare the unrounded ratio with the expected chemistry and the experiment's uncertainty. This tool does not apply a universal tolerance or claim that the nearest integer is correct.

What the calculation assumes

• The residue has the anhydrous formula you entered.
• The measured loss is water, without loss or decomposition of the salt.
• The starting and final masses refer to the same sample and container basis.

Incomplete water removal, moisture uptake, sample loss or a wrong residue formula can change the result. A noninteger ratio by itself cannot identify which problem occurred. Follow the original laboratory method for evaluating a constant mass; do not invent a new heating step from a calculator result.

Already know the hydrate formula? Enter the complete formula, including the dot and water count, in the main grams to moles calculator. For a solution made with that compound, the molarity calculator uses the final solution volume.

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