## nellysmith Does anybody know please how to calculate the percent water of KAl(SO4)2•12 H2O? 2 years ago 2 years ago

the formula of the hydrate tells us that 1 unit of alum (the salt) will be surrounded by 12 water molecules. This ratio is constant, so a MOLE of alum will have 12 MOLES of water surrounding it. The molar masses of these pieces are easy to find. The % water is calculated by:$\%H{_2}O = \frac{MM (H{_2}O)}{MM(hydrate)} * 100\%$ I get about 54.4% water