Question

when 10.00 g of phosphorus reacts with oxygen, it produces 17.77 g of a phosphorus oxide. This phosphorus oxide was found to have a molecular mass of approximately 220 g/mole. Determine the molecular formula.

Answer 1

Answer:

Molecular formula = P₄O₆

Explanation:

P(s)         +        O₂(g)------------------------------------⇒ PₓOₙ (g)

10g                     (17.77-10)g                                    17.77g

10g                        7.77g                                          17.77g  (gramme ratio)

The molecular mass of Phosphorus  (P) = 31g/mole

The molecular mass of Oxygen atom (O) = 16g/mole

Mole ratio is given by:

P              :             O

10/31                    7.77/16

0.3226       :         0.4856                Mole ratio---------------------------- (1)

Divide (1)  through by 0.3226

 1                 :        1.5-------------------------------------------- (2)

From  (2), the empirical formula for Phosphorus oxide :

Empirical formula = P₁O₁.₅

                               =  PO₁.₅

The molecular formula can be calculated from below:

Since the molecular formula is a multiple of the empirical formula we have

Molecular formula = (PO₁.₅)ₙ----------------------------------- (3)

Since we are given the molecular mass of the oxide formed, we have:

(PO₁.₅)ₙ = 220-----------------------------(4)

[31 + (16 x 1.5)] x n = 220

[31 + 24]n = 220

55n =220

n = 4

Substituting into (3), we have :

Molecular formula = (PO₁.₅)₄

                               = P₄O₆