Question

4) A 5.000 g sample that contained NaCl and Bacl2.2H20 was heated. After heating the sample had a weight of 4.488 g. What is the percent NaCl in the sample?

Answer 1

mass of water lost by BaCl2 = 5.000 - 4.488 = 0.512 g

mass of NaCl + BaCl2 = 4.488 g

moles of H2O = mass / molar mass = 0.512 g/ 18 g/mol = 0.0284 mol

The ratio between H2O and BaCl2 is 2 : 1

Hence,

moles of BaCl2 = moles of water /2 = 0.0284/2 = 0.0142 mol

mass of BaCl2 = moles x molar mass = 0.0142 mol x 208.23 g/mol= 2.956 g

Then,

mass of NaCl = mass of NaCl + BaCl2 - mass of BaCl2 = 4.488 g - 2.956 g = 1.532 g

% NaCl = (mass of NaCl / mass of sample) x 100

           =   (1.532 g / 5 g) x 100

          = 30.64 %

Therefore, percent NaCl in the sample = 30.64 %