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Consider 100 ml of 0.3 molar solution formed by dissolving 3.33g of XCl2 in water. What is the molar mass of element X? (Atomic mass of Cl = 35.5)(a) 9(b) 24(c) 40(d) 87The question was asked in an interview.My enquiry is from Expressing Concentration of Solutions topic in division Solutions of Chemistry – Class 12

Answer»

Right option is (c) 40

To explain I would say: Given,

CONCENTRATION, c = 0.3 MOLE/L

Volume, v = 100 ml = 0.1 L

Number of moles, n = concentration (mole/L) x volume (L)

n = 0.3 mole/L x 0.1 L = 0.03 moles

0.03 moles of XCL2 corresponds to 3.33g, then 1 mole CONTAINS 3.33/0.03 = 111 g of XCl2.

Hence, molecular mass = 111 g/mole.

Let x be the atomic mass. Then –

111 = x + 2(35.5)

x = 40g/mole.



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