Practice!

Sample Problem

When hydrates are heated, the water molecules jiggle loose from between the ions and only the anhydrous salt remains.  What percent by mass water is present in MgCO3·3H2O?  %.

Solution

Percent composition of water = mass of water / mass of hydrate

[3 × ( 2 + 16 )] ÷ [24 + 12 + 3 × 16 + 3 × (2 + 16)] × 100 % = 39 %