Substance X raises the boiling point of 150g of water to 101.3 C. What is the molecular mass of substance X? (assume x does not ionize/ is not volatile)
delta T = K b*molality.
molality = mols/kg solvent
what is the value for Kb? .52?
Yes, Kb is 0.52 for water.
By the way, the Kf for water is 1.86 degrees c/m. I think I may have given you 0.52 for the freezing point constant in an earlier problem.
Yes, I just wanted to verify it was the same thanks
It isn't the same. Kf for water is 1.86.
Kb for water is 0.52
To find the molecular mass of substance X, we need to use the colligative properties of a solution, specifically the boiling point elevation. The boiling point of a solvent increases when a non-volatile solute is added to it.
The formula to calculate the boiling point elevation (ΔTb) is:
ΔTb = Kb * m
Where:
- ΔTb is the change in boiling point
- Kb is the molal boiling point elevation constant (a constant specific to the solvent)
- m is the molality of the solute
In this case, the solute is substance X and the solvent is water. Since substance X does not ionize or is not volatile, we can assume it does not dissociate into ions or molecules in water and is therefore a non-electrolyte.
Given:
- ΔTb = 101.3 °C (boiling point elevation)
- mass of water = 150 g
The molal boiling point elevation constant for water (Kb) is approximately 0.512 °C/m.
We can now rearrange the formula to solve for the molality (m):
m = ΔTb / Kb
Substituting the known values:
m = 101.3 °C / 0.512 °C/m
m ≈ 198.04 mol/kg
The molality (m) represents the number of moles of substance X per kilogram of water.
Now, to find the molecular mass of substance X, we need to calculate the number of moles of substance X dissolved in the water.
moles of substance X = molality * mass of water (in kg)
mass of water (in kg) = 150 g / 1000 = 0.15 kg
moles of substance X = 198.04 mol/kg * 0.15 kg
moles of substance X ≈ 29.706
Finally, to determine the molecular mass (M) of substance X, we divide the mass of substance X by the moles of substance X:
M = mass of substance X / moles of substance X
Assuming the mass of substance X is given, you can substitute it into the formula to find the molecular mass.