A sample of impure NaHCO3 with an initial mass of 0.654 g yielded a solid residue (consisting of Na2CO3 and other solids) with a final mass of 0.456 g. Determine the mass percent of NaHCO3 in the sample.

Explanation:

Mass of impure NaHCO3 = 0.654g

Mass of residue= 0.456g

Mass loss of NaHCO3= 0.654-0.456= 0.198g

Balanced reaction equation:

2NaHCO3(s)> Na2CO3(s) + H2O(g)+CO2(g)

Note CO2 and water vapour produced in the decomposition combines to give H2CO3

84g of NaHCO3 yields 62g of H2CO3

Xg of NaHCO3 yields 0.198g of H2CO3

Therefore X= 84 × 0.198/ 62

=0.268g

Mass%= 0.268/0.654 × 100

=41% NaHCO3