when a certain amount of calcium chloride (CaCl2) was dissolved 100.g of water, the boiling point rose from 100.0*C to 104.4*C; calculate the molality of this solution.
delta T = i*Kb*m
delta T = 4.4
i for CaCl2 = 3
Kb for water you know
solve for m.
To calculate the molality (m) of a solution, you need to know the amount of solute (in moles) and the mass of the solvent (in kilograms).
Step 1: Calculate the molality of the solution.
Molality (m) is defined as the moles of solute per kilogram of solvent.
Given:
Mass of water (solvent) = 100.0 g = 0.100 kg
Boiling point elevation (ΔTb) = 104.4°C - 100.0°C = 4.4°C
Step 2: Convert the boiling point elevation (ΔTb) into kelvin (K).
Kelvin temperature (ΔTb) = 4.4°C + 273.15 = 277.55 K
Step 3: Calculate the molal concentration (molality) of the solution.
The boiling point elevation (ΔTb) is related to the molality (m) of the solution by the equation:
ΔTb = Kb * m
where Kb is the molal boiling point elevation constant for the solvent. For water, Kb is approximately 0.512 °C/molal.
Rearranging the equation gives:
m = ΔTb / Kb
Substituting the known values:
m = 277.55 K / 0.512 °C/molal
Step 4: Convert the temperature increase back to Celsius to get the molality.
m = 541.6 °C/molal
Therefore, the molality of the solution is 541.6 °C/molal.