Calculation of Molality of Ammonia

To find the molality of ammonia in the given solution, we need to follow a few steps.

Step 1: Calculate the number of moles of ammonia (NH3)

To calculate the number of moles, we can use the formula:

Number of moles = Mass / Molar mass

The molar mass of ammonia (NH3) is calculated by adding the atomic masses of nitrogen (N) and hydrogen (H):

Molar mass of NH3 = (1 × atomic mass of N) + (3 × atomic mass of H)

Using the atomic masses from the periodic table, the molar mass of ammonia is:

Molar mass of NH3 = (1 × 14.01 g/mol) + (3 × 1.01 g/mol) = 17.03 g/mol

Now, we can calculate the number of moles of ammonia:

Number of moles = 0.85 g / 17.03 g/mol = 0.0499 mol

Step 2: Calculate the mass of the liquid

We are given the density of the liquid as 0.85 g/cm^3 and the volume of the liquid as 100 mL. To calculate the mass of the liquid, we can use the formula:

Mass = Density × Volume

Converting mL to cm^3:

Volume = 100 mL = 100 cm^3

Now, we can calculate the mass of the liquid:

Mass = 0.85 g/cm^3 × 100 cm^3 = 85 g

Step 3: Calculate the molality

Molality is defined as the number of moles of solute per kilogram of solvent. In this case, the solvent is the liquid.

To calculate the molality, we can use the formula:

Molality = Number of moles of solute / Mass of solvent (in kg)

Converting the mass of the liquid from grams to kilograms:

Mass of solvent = 85 g / 1000 = 0.085 kg

Now, we can calculate the molality:

Molality = 0.0499 mol / 0.085 kg = 0.587 mol/kg

Conclusion:

The molality of ammonia in the given solution is 0.587 mol/kg.