Question

# A pure sample of cobalt chloride weighing 1.30 g was found to contain 0.59 g of cobalt and 0.71g of chloride on quantitative analysis. If the percentage composition of cobalt = x% and chloride = y%, then the value of x and y are, respectively(a) 45.4,54.6(b) 40.2,60.4(c) 50.0,50.2(d) None of the above

Hint: According to the law of definite composition which states that in a compound, the elements are present in a definite proportion by mass and the percentage purity of any substance/ material  can be calculated by dividing the mass of the each element by the total mass of the compound and then multiplying it by 100.

1 g of the compound of cobalt chloride contains = $\frac {0.59} {1.30}$g of Co 100 g of the compound of cobalt chloride contains = $\frac {0.59\times 100} {1.30}$g of Co = 45.38%
1 g of the compound of cobalt chloride contains = $\frac {0.71} {1.30}$g of Cl 100 g of the compound of cobalt chloride contains = $\frac {0.71\times 100} {1.30}$g of Cl = 54.61%