When 2.50g of an unknown solute is dissolved in 40.0g of ethanol the solution boils at 79.4C. The normal boiling point of this substance is 78.4C and it has a kb of 1.22C/m.
(a) What is the molality of this solution?
(b) What is the molecular weight of the solute?
delta T = Kb*m
Solve for m
molality = grams/molar mass
solve for molar mass.
To find the molality of the solution, you need to calculate the moles of solute dissolved in the given mass of ethanol.
(a) First, find the moles of the solute:
To do this, you can use the formula:
moles = mass / molar mass
Given:
Mass of solute = 2.50 g
To calculate the molar mass of the solute, we need additional information. However, we can use the provided data to find the molecular weight in part (b) and then come back to part (a).
(b) To find the molecular weight of the solute, we can use the equation:
Change in boiling point = kb * molality
Given:
Change in boiling point (ΔTb) = 79.4°C - 78.4°C = 1.0°C
Kb = 1.22°C/m
Rearranging the equation, we get:
molality = ΔTb / Kb
Substituting the values:
molality = 1.0°C / 1.22°C/m
Now that we have the molality, we can go back to part (a) and find the moles of solute:
(a) moles = mass / molar mass
moles = 2.50 g / molar mass
Solve for the molar mass by rearranging the equation:
molar mass = mass / moles
Substituting the given values:
molar mass = 2.50 g / moles
Now that we have both the molality and the molar mass of the solute, we can proceed to calculate the answers.