1. You are given a sample of green nickel sulfate hydrate for analysis. You weig
ID: 569657 • Letter: 1
Question
1. You are given a sample of green nickel sulfate hydrate for analysis. You weigh the sample in a dry covered crucible and obtain a mass of 22. 068 g for the crucible, cover and sample. The mass of the empty crucible and cover had been found earlier to be 21.214 g. You then heat the crucible to drive off the water of hydration, keeping the crucible at red heat for 10 minutes with cover slightly ajar. On cooling, you find the mas of the crucible, cover and dehydrate to be 21.717 g. The sample was converted in the process to yellow solid anhydrous Niso4 a. what is the mass of the hydrate sample? g b. what is the mass of the anhydrous Niso.? g c. what is the mass of the water driven off? d. What is the percent water in the hydrate? 8 % water = [mass of water in sample / mass of hydrate) x 100 % How many moles of water would there be in 100.0 g of hydrate? (Use the results in Part d to find the number of grams of water in a 100.0 g sample of hydrate and convert that amount to moles.) e. moles H20 f. How many moles of NisOs are there in 100.0 g of hydrate? (What percent of the hydrate is Niso.? Find the number of grams of NiSO4 in 100.0 g of hydrate. Convert that mass to moles of Niso4.) moles NiSO 8. How many moles water are present per mole of NiSO4 h. What is the formula for the hydrate? 2. What is the meaning of "heating to constant weight"? Why is it done?Explanation / Answer
1.
(a)
Mass of hydrate sample = 22.068 - 21.214 = 0.854 g.
(b)
Mass of anhydrous NiSO4 = 21.717 - 21.214 = 0.503 g.
(c)
Mass of the water driven off = 0.854 - 0.503 = 0.351 g.
(d)
% mass of water = 0.351 * 100 / 0.854 = 41.10%
(e)
Mass of water in 100.0 g. of hydrate = 41.1 g.
Moles of water = mass / molar mass = 41.1 / 18 = 2.28 mol
(f)
Mass of NiSO4 = 100 - 41.1 = 58.9 g.
Molar mass of NiSO4 = 154.8 g/mol
Moles of NiSO4 = 58.9 / 154.8 = 0.380 mol
(g)
0.380 mol of NiSO4 has 2.28 mol of water
then,
1 mol of NiSO4 has 2.28 / 0.380 = 6 mol of water
(h)
Formula of hydrate = NiSO4.6H2O
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