Question

1. The Na2S that we are using for this lab is a hydrated solid. That is, there are water molecules absorbed within the solid itself. You will be using 60% Na S; 60% of the mass of this solid is Na2S and the other 40% is water. For example, if you have a 10 gram sample of Na S (60%), 6 grams is Na2S and 4 grams is H,O. a. You will be using 0.1 gram quantities of NazS (60%) in this lab. In grams, how much of this sample is Na2S? b. Using your answer to part a, calculate how many moles of Na2S are in a 0.1 gram sample of Na2S (60%).

Answer 1

(a) 10 g of Na₂S (60%) contains 6 g Na₂S

$\Rightarrow$ 1 g of Na₂S (60%) contains 6/10 g Na₂S

$\Rightarrow$ 0.1 g of Na₂S (60%) contains (6/10) X 0.1 g Na₂S = 0.06 g Na₂S

(b) number of moles = mass / molar mass = 0.06 g / 78.045 g mol^-1 (molar mass of Na₂S = 78.045 g mol^-1)

number of moles of Na₂S = 0.000769 mol = 7.69 X 10^-4 mol

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