Derive the chemical formula of a substance if it is known that a) w (Ca) = 36%, w (Cl) = 64%

Derive the chemical formula of a substance if it is known that a) w (Ca) = 36%, w (Cl) = 64% b) w (Na) 29.1 =%, w (S) = 40.5%, w ( O) = 30.4%

The mass fraction of the element in the compound is calculated by the following formula:

w (X) = n * A (X) / Mr.

The molar mass of the compounds is unknown, but the same in each case (a, b). If we know the ratio of the mass fraction and atomic mass of an element, then we can find the number of atoms n.

w (X) / A (X) = n / Mr = constant.

a). w (Ca) / A (Ca) = 36/40 = 0.9

w (Cl) / A (Cl) = 64 / 35.5 = 1.8

Divide the larger number by the smaller and get the ratio of atoms in the compound.

n (Ca) / n (Cl) = 0.9 / 1.8 = 1/2

Formula: CaCl2.

b). w (Na) / A (Na) = 29.1 / 23 = 1.26

w (S) / A (S) = 40.5 / 32 = 1.26

w (O) / A (O) = 30.4 / 16 = 1.9

n (Na) / n (S) / n (O) = 1.26 / 1.26 / 1.9 = 1/1 / 1.5 = 2/2/3

Formula: Na2S2O3.