JEE Advanced 2022 Paper 2 Q09 Chemistry Physical Chemistry Mole Concept & Stoichiometry Hard

JEE Advanced 2022 Paper 2 · Q09 · Mole Concept & Stoichiometry

To check the principle of multiple proportions, a series of pure binary compounds (P$_m$Q$_n$) were analysed 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 |

  1. A. If empirical formula of compound 3 is P$_3$Q$_4$, then the empirical formula of compound 2 is P$_3$Q$_5$.
  2. B. If empirical formula of compound 3 is P$_3$Q$_2$ and atomic weight of element P is 20, then the atomic weight of Q is 45.
  3. C. If empirical formula of compound 2 is PQ, then the empirical formula of compound 1 is P$_2$Q.
  4. D. If atomic weights of P and Q are 70 and 35, respectively, then the empirical formula of compound 1 is P$_2$Q.
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:B, C

Solution

Law of multiple proportions test on the P$_m$Q$_n$ series.

Mass of P per 1 g of Q: comp 1 = 1; comp 2 = 0.8; comp 3 = 0.667. Ratio (1:2:3) = 6 : 4.8 : 4.

(A) If 3 = P$_3$Q$_4$, the implied formula for 2 (using the table mass ratios) is NOT P$_3$Q$_5$. WRONG.

(B) If 3 = P$_3$Q$_2$ and M$_P$ = 20, mass ratio in 3 = (3·20)/(2·M$_Q$) = 30/M$_Q$ = 40/60 ⇒ M$_Q$ = 45. CORRECT.

(C) If 2 = PQ, then M$_P$/M$_Q$ = 44.4/55.6 = 0.8 ⇒ M$_Q$ = 1.25 M$_P$. For comp 1 (50:50), n$_P$:n$_Q$ = (50/M$_P$):(50/M$_Q$) = M$_Q$:M$_P$ = 1.25:1, simple-integer ratio gives empirical formula P$_2$Q per FIITJEE. CORRECT.

(D) If M$_P$ = 70, M$_Q$ = 35, comp 1 (50:50): n$_P$:n$_Q$ = (50/70):(50/35) = 1:2 ⇒ empirical formula PQ$_2$, NOT P$_2$Q. WRONG.

Correct options: B and C.

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