What is the boiling point of a 25.20% (m/v) KNO3 solution ? (Kf of water = 1.86
0C/molal) (Kb of water = .52 0C/molal) (molar mass potassium nitrate = 101.10324 g/mole)
The density of the solution is 1.09 g/ml
What is the molarity of the solution?
What is the molality of the solution?
What is the boiling point of the solution?
To find the molarity of the solution, we need to know the number of moles of solute (potassium nitrate, KNO3) and the volume of the solution.
1. Convert the percentage mass/volume (m/v) to grams per milliliter (g/mL):
- The density of the solution is given as 1.09 g/mL.
- This means that for every 1 mL of solution, there are 1.09 grams of solution.
2. Calculate the mass of the solute (KNO3) in the solution:
- Multiply the volume of the solution (in mL) by the density (in g/mL) to get the mass of the solution in grams.
- Since we have a percentage mass/volume, we assume that 100 mL of the solution contains 25.20 grams of KNO3.
3. Convert the mass of KNO3 to moles:
- Divide the mass of KNO3 by its molar mass (101.10324 g/mol) to get the number of moles of KNO3 in the solution.
4. Finally, calculate the molarity of the solution (moles of solute per liter of solution):
- Divide the number of moles of KNO3 by the volume of the solution in liters (which is the same as the volume in mL divided by 1000).
To find the molality of the solution, we need to know the number of moles of solute (KNO3) and the mass of the solvent (water) in kilograms.
1. Calculate the mass of the solvent in grams:
- Since we know the density of the solution is 1.09 g/mL and the volume of the solution in mL, we can multiply the volume by the density to get the mass of the solution in grams.
- Subtract the mass of KNO3 from the total mass of the solution to get the mass of the solvent (water) in grams.
2. Convert the mass of the solvent to kilograms:
- Divide the mass of the solvent (water) by 1000 to convert it to kilograms.
3. Calculate the molality of the solution (moles of solute per kilogram of solvent):
- Divide the number of moles of KNO3 by the mass of the solvent in kilograms.
To find the boiling point of the solution, we can use the equation for boiling point elevation:
ΔTb = Kb * m
where ΔTb is the boiling point elevation, Kb is the boiling point elevation constant (provided as 0.52 °C/molal), and m is the molality of the solution.
1. Plug in the given value for Kb and the calculated value for molality to calculate ΔTb.
2. Add ΔTb to the boiling point of pure water (100 °C) to find the boiling point of the solution.
Note: In this case, since the density and molar mass of the solute are provided, we don't need to convert between mass/volume and mass/mass.