Answer:
a. 2.41 molal
b. 0.21 M
c. 58.5 mL
Explanation:
First of all let's think the data 10 % by mass, which means, that 10 grams from the solute is contained in 100 g of this solution.
So If we know solution density, we can get its volume.
Solution density = Solution mass / Solution volume
0.984 g/ml = 100 g / Solution volume
Solution volume = 100 g/ 0.984g/ml
Volume = 101.6 mL
As we have 10 g of solute, 100 g of solution, we have 90 g of solvent.
Solute mass + Solvent mass = Solution mass
How many moles do we have in 10 g of ethanol?
Molar mass of ethanol: 46.07 g/m
Mass / molar mass = Moles
10 g/ 46.07 g/m = 0.217 mol
This quantity is in 90 g of solvent and 101.6 mL of solution. For molality and molarity, we should use a rule of three to find out the moles in 1 kg of solvent and 1 L of solution.
1 L = 1000 mL
1kg = 1000 g
Molality
90 g _____ 0.217 moles
1000 g _____ (1000 . 0.217)/ 10 = 2.41 molal
Molarity
101.6 mL ___ 0.217 moles
1000 mL ____ (1000 . 0.217) / 101.6 = 0.21 M
What volume of the solution would contain 0.125 mole of ethanol?. Let's think a new rule of three.
0.217 moles of solute ___ are in __ 101.6 mL of solution
0.125 moles of solute___ are in (0.125 . 101.6)/0.217 = 58.5 mL
