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Compounds AB and AB2 (or PQ and PQ2) raise the boiling point by different amounts: find the atomic masses

The same question, asked 2 times: 2 Apr 2025*, 21 Jan 2026 S1. Every wording below, oldest first.

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  1. Question 1

    2 Apr 2025

    124
    When 1 g each of compounds AB and AB2{AB}_{2} are dissolved in 15 g of water separately, they increased the boiling point of water by 2.7 K and 1.5 K respectively. The atomic mass of A (in amu) is ____ ×10−1\times 10^{- 1} (Nearest integer).(Given : Molal boiling point elevation constant is 0.5 K kg mol−10.5\text{ }K\text{ }kg{\text{ }mol}^{- 1} )

  2. Question 2

    21 Jan 2026 S1

    34
    Elements P and Q form two types of non-volatile, non-ionizable compounds PQ and PQ2PQ_{2}. When 1 g of PQ is dissolved in 50 g of solvent ' A '. ΔTb\Delta T_{b} was 1.176 K while when 1 g of PQ2PQ_{2} is dissolved in 50 g of solvent ' A ', ΔTb\Delta T_{b} was 0.689 K. (KbK_{b} of ' A ' =5 Kkgmol−1= 5\text{ }Kkgmol^{- 1}). The molar masses of elements P and Q (in gmol−1gmol^{- 1}) respectively, are :

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