5.70 g of NH4Cl is added to 13.3 g of water. Calculate the molality of the solution.
moles NH4Cl = grams NH4Cl/molar mass
m NH4Cl = moles/kg solvent.
7.30 g of NH4Cl is added to 11.9 g of water. Calculate the molality of the solution.
To calculate the molality of a solution, you need to know the amount of solute (in moles) and the mass of the solvent (in kilograms). Here's how you can calculate the molality of the solution:
Step 1: Convert the mass of NH4Cl to moles.
The molar mass of NH4Cl is calculated by adding up the atomic masses of its constituent elements: nitrogen (N), hydrogen (H), and chlorine (Cl). The atomic masses of N, H, and Cl are approximately 14.01 g/mol, 1.01 g/mol, and 35.45 g/mol, respectively.
Molar mass of NH4Cl = [1 mol NH4Cl = (1 mol N + 4 mol H + 1 mol Cl)]
= (14.01 g/mol + 4 * 1.01 g/mol + 35.45 g/mol)
≈ 53.49 g/mol
To convert the mass of NH4Cl to moles, divide the mass (5.70 g) by the molar mass of NH4Cl:
moles of NH4Cl = (mass of NH4Cl) / (molar mass of NH4Cl)
= 5.70 g / 53.49 g/mol
≈ 0.107 mol
Step 2: Convert the mass of water to kilograms.
Since the molality of a solution is expressed in moles of solute per kilogram of solvent, you need to convert the mass of water to kilograms by dividing it by 1000:
mass of water (in kg) = (mass of water) / 1000
= 13.3 g / 1000
= 0.0133 kg
Step 3: Calculate the molality.
The molality (m) is calculated by dividing the number of moles of solute (NH4Cl) by the mass of solvent (water) in kilograms:
molality (m) = (moles of solute) / (mass of solvent in kg)
= 0.107 mol / 0.0133 kg
≈ 8.02 mol/kg
Therefore, the molality of the solution is approximately 8.02 mol/kg.