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Calculate Molarity and Molality of 6.3% Solution of Nitric Acid Having Density 1.04 G Cm−3

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Question

Calculate molarity and molality of 6.3% solution of nitric acid having density 1.04 g cm−3
. (H = 1, N = 14, O = 16)

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Solution

Given: Density of 6.3% HNO3 = 1.04 g cm−3

To find: a. Molarity b. Molality

Formulae:

a) Molarity = Number of moles of solute/Volume of solution in L b) Molality = Number of moles of solute/Mass of solvent in kg

Calculation: Density of solution = Mass of solution/Volume of solution

∴ Volume of solution = `100/1.04` = 96.15 cm3 = 96.15 × 10–3 dm3

Molarity = `"Massof solute"/"Molar mass of solute×Volume of solution in L"`

∴ Molarity  = `(6.3 xx 10^(-3))/(63 xx 10^(-3) xx 96.15 xx 10^(-3))` = 1.04 mol/dm3

b) 6.3% HNO3 is present means 6.3 g of HNO3 is present in 100 g of solution.

Mass of H2O = 100 − 6.3 = 93.7 g

Molality of HNO3 = Massof HNO3/Molar mass of HNO3 ×Massof solvent in kg

`= (6.3 xx 10^(-3))/(63xx10^(-3) xx 93.7 xx 10^(-3))`

= 1.067 mol/kg

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2012-2013 (October)

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