University:
California State University San Marcos
Course:
CHEM 160 | General Chemistry II
Academic year:

2020
Views:

259

Pages:

2
Author:

Yemima C.

Determining Hydrate Chemical Formulas Hydrates are solids that bind several water molecules as part of their crystal structure. Example: 1. Continue (CuSO4 .5 H2 O) : copper(II) sulfate pentahydrate 2. Gypsum (CaSO4 .2 H2 O) : calcium sulfate dihydrate 3. English salt (MgSO4 .7 H2 O) : magnesium sulfate heptahydrate 4. Rock soda(Na2 CO3 .10 H2 O) : decahydrate sodium carbonate If a hydrate compound is heated, then some or all of the crystal water can be released (evaporates). If a hydrate is dissolved in water, the water crystals will be released. Example: CuSO4 .5 H2 O(s) CuSO4 (aq) + 5 H2 O(l) The number of crystal water molecules of a hydrate compound can be determined in the following way. Example 1. As much as 5 grams of hydrate of copper(II) sulfate (CuSO4 .5 H2O ) is heated until all the crystalline water has evaporated. If the solid mass of copper(II) sulfate formed is 3.2 grams, determine the formula of the hydrate! (Ar Cu = 63.5, S = 32, O = 16, and H = 1). Answer: The mass of H2 O = 5 grams – 3.2 grams = 1.8 grams Equation for heating reaction CuSO4 .5 H2 O: CuSO4 .x H2 O(s) 0.02 mol 0.1 mol CuSO4 (s) + x H2 O(l) Mole ratio : CuSO4 : H2 O = 0.02 mol : 0.1 mol = 1 : 5 Because the mole ratio = coefficient ratio, then x = 5. So, the formula of the hydrate is CuSO4 .5 H2 O. Exercise 1. 1. As much as 2 grams of calcium chloride (CaCl2 ) absorbs moisture from the air and forms hydrate with a mass of 3.94 grams. Determine the hydrate formula! (Ar Ca = 40, Cl = 35.5, H = 1, and O = 16) 2. The water content of crystals in a hydrate of sodium carbonate (Na2 CO3 ) is 14.5%. Determine the hydrate formula! (Ar Na = 23, C = 12, O = 16, and H = 1) 3. As much as 15 grams of hydrate of iron(II) sulfate (FeSO4 .x H2O ) is heated until all the crystalline water has evaporated. If the mass of solid iron(II) sulfate formed is 8.2 grams, determine the formula of the hydrate! (ArFe = 56, S = 32, O = 16, and H = 1) 4. On the crystallization of 3.19 grams of copper(II) sulfate (CuSO4 ) 4.99 grams of hydrate CuSO4 .x H2 O is formed. Determine the formula of the hydrate! (Ar Cu = 63.5, S = 32, O = 16, and H = 1) 5. Copper(II) nitrate crystals have the formula Cu(NO3 )2 .x H2 O. If the crystals contain 36.54% water, determine the formula of the hydrate! (Ar Cu = 63.5, N = 14, O = 16, and H = 1) 6. If 38 grams of MgSO4 x H2O is heated, 20 grams of anhydrous MgSO4 will be produced . Determine the hydrate formula! (ArMg = 24, S = 32, O = 16, and H = 1) 7. When the compound copper(II) sulfate hydrate (CuSO4 .x H2 O) is heated, it loses 36% in weight. Determine the hydrate formula! (Ar Cu = 64, S = 32, O = 16, and H = 1)