6.7 – NOTES Hydrates

4. Hydrates Definition: salt crystal with water molecules inside the crystal; if water is removed the substance becomes an anhydrous; CuSO4  5 H2O + heat  CuSO4 + 5 H2O

CuSO4 + 5 H2O

Naming hydrates the salt is named as an ionic compound; the water is named with the word hydrate; a prefix is placed in front of hydrate to show how many water molecules are found inside the salt crystal;   1 = mono 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deca For example – CuSO4  5H2O = copper II sulfate pentahydrate

Percentage composition of compounds (review of Chapter 3) and percentage composition of hydrates. Similar to finding % composition; when adding up the elements add up water as H2O; Example: Determine the percentage composition of sodium oxide. Na2O Na = 2 x 23.0 = 46.0 % Na = 46.0 / 62.0 x 100 = 74.2% O = 1 x 16.0 = 16.0 % O = 16.0 / 62.0 x 100 = 25.8% 62.0 g/ mol

Determine the percentage of water in Na2CO3 • 10 H2O. Na = 2 x 23.0 = 46.0 % H2O = 180. / 286 x 100 = 62.9% C = 1 x 12.0 = 12.0 O = 3 x 16.0 = 48.0 106.0 H2O = 10 x 18.0 = 180. 286  

Example: CuSO4 • 5H2O Name the compound, then write the equation for the heating of this compound. CuSO4 • 5 H2O = copper (II) sulfate (or cupric sulfate) pentahydrate CuSO4 • 5 H2O  CuSO4 + 5 H2O (anhydrous + water) water driven off as vapor

B. Determine the % of water in this compound. Cu = 63.5 90.0 x 100 = 36.1% S = 32.1 249.6 O = 64.0 (= 4x16.0) H2O = 90.0 (= 5x18.0) 249.6