P and Q

Chemistry Level 3

$\ce P$ and $\ce Q$ are two elements which form $\ce{P2Q3}$ and $\ce{PQ2}$ molecules. If $0.15\text{ mole}$ of $\ce{P2Q3}$ and $\ce{PQ2}$ weighs $15.9\text{ g}$ and $9.3\text{ g}$ , respectively, what is the sum of atomic masses of $\ce P$ and $\ce Q$ ?

The answer is 44.

1 solution

Abhiram Rao
May 1, 2016

Let atomic weight of P be x and atomic weight of Q be y, then atomic weight of P2Q3 = 2x + 3y. Similarly atomic weight of PQ2 is x + 2y.

So, weight if 0.15 moles of P2Q3 = 0.15 × (2x + 3y) = 15.9. 0.3x + 0.45y = 15.9 (1)

Weight of 0.15 moles of PQ2 = 0.15 × (x + 2y) = 9.3 0.15x + 0.3y = 9.3 (2)

Multipying the equation above by 2, we get:- 0.3x + 0.6y = 18.6

Subtracting (1) from (2), we get:- 0.15y = 2.7 y = 18

Substituting y=18 in (1) , we get:- 0.3x + 0.45 × 18 = 15.9 0.3x = 15.9 - 8.1 0.3x = 7.8 x = 26

x+y=18+26=44

P and Q

The answer is 44.

1 solution

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