Question

What is the molality of nitric acid in a concentrated solution of nitric acid (68.0% HNO3 by mass)? (a) Outline the steps necessary to answer the question. (b) Answer the question

Answer 1

Answer:

The molality of HNO3 is 33.75 molal

Explanation:

Step 1: Data given

mass % of HNO3 = 68 %

Step 2: Calculate masses

If the mass % of HNO3 is 68 %, this means that 68 of 100 grams are HNO3

This means that 100-68 = 32 grams are water.

So mass HNO3 = 68 grams

Mass H2O = 32 grams

mass solution = 100 grams

Step 3: Calculate moles HNO3

Moles HNO3 = mass HNO3 / molar mass HNO3

Moles HNO3 = 68.0 grams / 63.02 g/mol

Moles HNO3 = 1.08 moles

Step 4: Calculate molality

Molality = number of moles HNO3 / mass of water

Molality = 1.08 moles / 0.0320 kg

Molality = 33.75 molal

The molality of HNO3 is 33.75 molal

Answer 2

Answer:

33.8 m

Explanation:

(a) We want to know the molality of nitric acid in a concentrated solution of nitric acid (68.0% HNO₃ by mass).

Step 1: Determine the mass of HNO₃ and water in 100 grams of solution.

Step 2: Convert the mass of HNO₃ to moles.

Step 3: Convert the mass of water to kilograms.

Step 4: Calculate the molality.

(b)

Step 1

In 100 g of solution, there are 68.0 g of HNO₃ and 100 g - 68.0 g = 32.0 g of water.

Step 2

The molar mass of HNO₃ is 63.01 g/mol. The moles corresponding to 68.0 g are:

68.0 g × (1 mol/63.01 g) = 1.08 mol

Step 3

The mass of water is 32.0 g = 0.0320 kg

Step 4

The molality of HNO₃ is:

m = moles of solute / kilograms of solvent

m = 1.08 mol / 0.0320 kg

m = 33.8 m