JEE Advanced 2022 · Paper 2 · Chemistry Q9

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ChemistryMultiple correct+4 / -2Question 45 of 54

To check the principle of multiple proportions, a series of pure binary compounds $(\mathrm{P_mQ_n})$ were analyzed and their composition is tabulated below. The correct option(s) is(are)

Compound	Weight % of P	Weight % of Q
1	50	50
2	44.4	55.6
3	40	60

If empirical formula of compound 3 is

\mathrm{P_3Q_4}

, then the empirical formula of compound 2 is

\mathrm{P_3Q_5}

If empirical formula of compound 3 is

\mathrm{P_3Q_2}

and atomic weight of element P is 20, then the atomic weight of Q is 45.

If empirical formula of compound 2 is PQ, then the empirical formula of the compound 1 is

\mathrm{P_5Q_4}

If atomic weight of P and Q are 70 and 35, respectively, then the empirical formula of compound 1 is

\mathrm{P_2Q}

Answer and worked solution

Official answer: B, C

Mass ratio. For $\mathrm{P_mQ_n}$ , the ratio of masses is $\dfrac{w_Q}{w_P}=\dfrac{n\,M_Q}{m\,M_P}$ . The three compounds have $\dfrac{w_Q}{w_P}=1,\ 1.252,\ 1.5$ .

Check each option.

(A) If 3 is $\mathrm{P_3Q_4}$ , then $\frac{M_Q}{M_P}=1.5\cdot\frac34=1.125$ . For compound 2, $\frac nm=\frac{1.252}{1.125}=1.11$ , not $\frac53$ . False.
(B) If 3 is $\mathrm{P_3Q_2}$ and $M_P=20$ , then $1.5=\frac{2M_Q}{60}$ , so $M_Q=45$ . True.
(C) If 2 is PQ, then $\frac{M_Q}{M_P}=1.252$ . For compound 1, $\frac nm=\frac1{1.252}=0.8=\frac45$ , which is $\mathrm{P_5Q_4}$ . True.
(D) With $M_P=70$ and $M_Q=35$ , compound 1 has $\frac nm=\frac{70}{35}=2$ , which is $\mathrm{PQ_2}$ , not $\mathrm{P_2Q}$ . False.

(B), (C).

Topics:Empirical and molecular formula Mole concept

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JEE Advanced 2022 · Paper 2, Chemistry question 9