DATE SECTION POSTLABORATORY ASSIGNMENT 1 Calculate the theoretical percentage of
ID: 580597 • Letter: D
Question
DATE SECTION POSTLABORATORY ASSIGNMENT 1 Calculate the theoretical percentage of water for the following hydrates. (a) calcium nitrate tetrahydrate, Ca(NO)2 4H20 (b) nickel(II) chloride hexahydrate, NiCl2 6H20 (c) zinc sulfate heptahydrate, ZnSO4-7H2O 2. An unknown hydrate, AC.MH2O, has a mass of 1.632 g and the anhydrous compound, AC, has a mass of 1.008 g. What is the experimental percentage of water in the hydrate? 3. If the anhydrous compound (AC) in the preceding problem has a molar mass of 146 g/mol, what are the water of crystallization (X0 and formula for the hydrate?Explanation / Answer
The percentage of water by mass in a hydrated salt is the ratio of mass of all the water molecules present in the hydrated salt to the mass of the hydrated of the salt converted into percentage. Thus, from the molar mass of water as 18.0152g/mol, that of calcium nitrate tetrahydrate as 236.15g/mol, nickel chloride hexahydrate as 237.683g/mol and that of zinc sulphate heptahydrate as 287.514g/mol, we can calculate the theoretical mass % of water as (Mass of water in salt/Mass of hydrated salt)x100.
This gives:
a) for calcium nitrate as (4x18.01528/236.15)x100 = 30.515%;
b) for nickel chloride (6x18.01528/237.683)x100 = 45.47% and
c) for zinc sulphate (7x18.01528/287.514)x100 = 36.558%.
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