Compute the freezing point of this solution: 25.5 g C7H11NO7S (4-nitro-2-toluenesulfoinoic acid dihydrate) in 100 g H2O. (nonionizing solute)
Freezing point depression= molality*Kf
You know Kf for water, so compute the molality of the solution, molessolute/kg of water
-.001853
To compute the freezing point of a solution, we need to use the formula for freezing point depression:
ΔTf = Kf * m
Where:
ΔTf = the change in freezing point
Kf = the cryoscopic constant, which is specific to the solvent
m = molality of the solute in the solution
In this case, the solute is non-ionizing, so we don't need to consider the Van't Hoff factor.
To find the molality (m) of the solute, we need to first calculate the number of moles of the solute using its molar mass.
1. Calculate the number of moles of the solute (C7H11NO7S):
- Determine the molar mass of C7H11NO7S:
Carbon (C) : 12.01 g/mol
Hydrogen (H) : 1.01 g/mol
Nitrogen (N) : 14.01 g/mol
Oxygen (O) : 16.00 g/mol
Sulfur (S) : 32.07 g/mol
Total molar mass: (7 * 12.01) + 11.01 + 14.01 + (7 * 16.00) + 32.07 = X g/mol (X is the molar mass)
- Calculate the number of moles of the solute using the given mass:
Moles of C7H11NO7S = given mass of C7H11NO7S / X
2. Calculate the molality (m) of the solute:
Molality (m) = moles of solute / mass of the solvent (in kg)
- Convert the given mass of water (H2O) to kg:
Mass of H2O = given mass of water / 1000
3. Plug in the values into the freezing point depression formula:
ΔTf = Kf * m
4. Finally, calculate the freezing point of the solution:
Freezing point of the solution = freezing point of the pure solvent - ΔTf
To find the cryoscopic constant (Kf) for water (H2O), you can refer to a reference source or use a standard value, which is 1.86 °C/molal.
By following these steps, you should be able to compute the freezing point of the given solution.