Quiz of the Day - Mono Mole

#1. Which is the best way to prepare 500 mL of a 2.00 M solution of aqueous H₂SO₄ from deionised water (M = 18.02, density = 1.00 g mL^-1) and concentrated H₂SO₄ (M = 98.08, density = 1.84 g mL^-1)?

Weigh 98.1 g concentrated sulphuric acid into a 500 mL beaker, then slowly add deionised water to the beaker, with occasional swirling, until the liquid reaches the 500 mL mark.

Weigh 98.1 g concentrated sulphuric acid into a 500 mL volumetric flask, slowly add deionised water to the mark, and mix.

Weigh 98.1 g concentrated sulphuric acid into a100 mL beaker, then slowly pour the H₂SO₄ into a 500 mL beaker with about 250 mL deionised water in it. Pour this solution into a 500 mL volumetric flask and fill to the mark with deionised water and mix.

Weigh 446.6 g deionised water into a 500 mL volumetric flask, fill to the mark with concentrated sulphuric acid, and mix.

You must always add acid to water in a stepwise dilution process, not water to acid. This is a standard laboratory safety rule. Adding water to concentrated sulphuric acid can cause violent splattering due to the highly exothermic nature of the dilution.

Assuming that concentrated sulphuric acid consists almost entirely of pure H₂SO₄ with negligible water, 98.1 g of the acid is equivalent to 1 mole of the acid, with a volume of 53.3 mL (1/0.0533 = 18.76 M). Topping up the solution to 500 ml is equivalent to a dilution of 500/53.3 = 9.38 times. The resulting molarity of the diluted acid is 18.76/9.38 = 2 M.

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