Chemistry question

Question

Consider the ionic compound, sodium sulfate decahydrate salt, Na₂SO₄.10H₂O 

a)      Calculate the molar mass of the salt and give appropriate units. Note the following atomic masses, Na = 23; S= 32; H = 1; and O = 16

 b)     Calculate the total mass of water in the salt  

c)    Calculate the percentage of water in the salt.

Answer 1

The molar mass of a compound (M) is the sum of the masses of the atoms that make up the compound expressed as grams per mole (g/mol).

So,

(a) M (Na₂SO₄.10H₂O) = (2 x 23 g/mol) + (1 x 32 g/mol) = (14 x 16 g/mol) + (20 x 1 g/mol) = 322 g/mol

(b) From the formula for the compound, we know that each mole contain 10 moles of water.

So, mass of H₂O = 10 moles x ( 2 g/mol + 16 g/mol) = 180 g

(c) % H₂O = (180 g/mol) / (322 g/mol) x 100% = 55.9%