Transcript Molarity and Molality

Molarity and
Molality
Molarity (M)
number of moles of solute (n) per
liter (L) of solution
Molarity (M) = Moles of Solute
Liters of Solution
Note: Moles = Mass of Solute
Molar Mass of Solute
1. What is the molarity of the solution if
3.0 mole of solute is dissolved in 12.0 L
solution?
Given:
Moles of Solute – 3.0 mole
Liters of Solution – 12.0 L
Formula: Molarity = Moles of Solute
Liters of Solution
Answer: M = Moles of Solute
Liters of Solution
= 3.0 mole
12.0L
= 0.25 M
2. What is the molarity of a 400.0 mL
solution containing 8.0 g NaOH?
Given:
Mass of Solute – 8.0 g of NaOH
Liters of Solution – 400.0 mL
Formula: Molarity = Moles of Solute
Liters of Solution
Answer: Moles = Mass of Solute
Molar Mass of Solute
= 8 g of NaOH
(23+16+1g/mole)
= 8 g NaOH
40 g/mole
= 0.2 mole
Given:
Molarity - ?
Liters of Solution – 400.0 mL
Moles of Solute – 0.2 mole
Formula: Molarity = Moles of Solute
Liters of Solution
Answer: M = Moles of Solute
Liters of Solution
= 400mL X 1 L
= 0.2 mole
1000mL
0.4 L
= 0.4L
= 0.5 M
3. How many grams of Ca(OH)2
are needed to prepare an 800.0 mL
solution of 0.015 M concentration?
Given:
Molarity – 0.015 M
Liters of Solution – 800.0 mL
Formula: Molarity = Moles of Solute
Liters of Solution
Answer: Moles = (Molarity) (Liters of Sol’n)
= 0.015 M (0.8 L)
= 800mL X 1 L
= 0.012 moles
1000mL
= 0.8L
Given:
Mass of Solute – ?
Moles of Solute – 0.012 mole
Molar Mass – Ca(OH)2 = [40+([16x2]+[1x2])] = 74g/mole
Formula: Moles = Mass of Solute
Molar Mass of Solute
Answer: Moles = Mass of Solute
Molar Mass of Solute
Mass of Solute = (Moles) (Molar Mass of Solute)
= (0.012moles) (74g/mole)
= 0.89 g
Molality (m)
as the number of moles of solute (n)
per kilogram (kg) of solution
Molality (m) = Moles of Solute
Kilograms of Solvent
Note: Moles = Mass of Solute
Molar Mass of Solute
1. What is the molality of a solution
containing 0.46 mole of solute in 2.0 kg
water?
Given:
Moles of Solute – 0.46 mole
Kilogram of Solvent – 2.0 kg
Formula: Molality = Moles of Solute
Kilogram of Solvent
Answer: m = Moles of Solute
Kilogram of Solvent
= 0.46 mole
2.0kg
= 0.23 m
2. What is the molality of a solution
containing 75.5 g Pb(NO3)2 in 400.0 g
water?
Given:
Mass of Solute – 75.5 g Pb(NO3)2
Molar Mass = [207+([14]2)+([16]6)]
= 331 g/mole
Formula: Moles = Mass of Solute
Molar Mass of Solute
Answer: Moles = Mass of Solute
Molar Mass of Solute
= 75.5 g
331 g/mole
= 0.23 moles
Given:
Molality – ?
Moles of Solute – 0.23 moles
Kilogram of Solvent – 400.0 g = 0.4kg
Formula: m = Moles of Solute
Kilogram of Solution
Answer: m = Moles of Solute
Kilogram of Solution
= 0.23 moles
0.4 kg
= 0.58 m
1. What mass of solute is needed to prepare each of
the following solutions?
a. 1.00 L of 0.125 M K2SO4
b. 375 mL of 0.015 M NaF
2. Calculate the molarity of each of the following
solutions:
a. 12.4 g KCl in 289.2 mL solution
b. 16.4 g CaCl2 in 0.614 L solution
3. Calculate the molality of each of the following
solutions:
a. 2.89 g of NaCl dissolved in 0.159 g of water
b. 1.80 mol KCl in 16.0 mol of H2O