Question

The method of continuous variation was applied to the complex formed between P and X. A plot of mole fraction X versus PaXb absorbance shows a maximum at 0.80. What is the stoichiometry for the complex?

(A) P2X3 (B) PX4 (C) PX5 (D) P3X2 (E) P4X

Correct Answer: (B) PX4

Answer 1

Mole fraction of P = moles of P/(moles of P+moles of X)

SImilarly,

Mole fraction of X = moles of X/(moles of P+moles of X)

For the plot of mole fraction X vs absorbance, it has maximum at 0.80.

This mole fraction of X = 0.80

If we say that moles of P = 1 mol

Let moles of X = x mol

Put his value in above equation,

Mole fraction of X = moles of X/(moles of P+moles of X)

0.80 = x/(1+x)

0.80(1+x) = x

0.80+0.80x = x

0.80 = 0.20x

x = 4

So, moles of X = 4 mol

Moles of P = 1 mol

The formula becomes PX₄