Que: A compound made up of two elements A and B has A= 70 %, B = 30 %. Their relative number of moles in the compound are 1.25 and 1.88. calculate a. Atomic masses of the elements A and B b. Molecular formula of the compound, if its molecular mass is found to be 160.
Ans. Relative no. of moles of an element = % of the element/Atomic mass
Atomic mass = % of the element/Relative no. of moles = 70/1.25 = 56
Atomic mass of B = 30/1.88 = 16
Calculation of Empirical formula
| Element | Relative no. of moles | Simplest molar ratio | Simplest whole no. molar ratio |
| A | 1.25 | 1.25/1.25 = 1 | 2 |
| B | 1.88 | 1.88/1.25 = 1.5 | 3 |
Empirical formula = A2B3
Calculation of molecular formula
Empirical formula mass = 2 x 56 + 3 x 16 = 160
n = molecular mass / Empirical formula mass = 160/160 = 1
Molecular formula = A2B3
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