Question

what is the molality of ammonia in a solution containing 0.85 grams of NH3 in 100 ml of a liquid of density of 0.85 g cm^-3?

Answer 1

Density = 0.85 grams/cm^3 = 0.85 grams/0.001L = 85grams/0.1L

Every 0.1L of that solution weights 85grams

There are 0.85 grams of NH3 in 100cm^3 = 0.85grams/0.1 solution

Mass of water in solution (0.1L) = 85-0.85 =84.15grams =0.08415kg

Number of moles of NH3 = Mass/Mw of NH3 = 0.85/17=0.05mol

Molality = Number of moles / mass of water in kg = 0.05/0.08415=0.597 Molal

Answer 2

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