Solutions

1
Solutions

• Molality

2
Molality (m)

• A concentration that expresses the
• moles of solute in 1 kg of solvent
• Molality (m) moles of solute
• 1 kg solvent

3
Units of Molality

• 2.0 m HCl 2.0 moles HCl
• 1 kg solvent
• 6.0 m HCl 6.0 moles HCl
• 1 kg solvent

4
Molality Calculation

• NaOH is used to open stopped sinks, to treat
• cellulose in the making of nylon, and to
• remove potato peels commercially.
• If 4.0 g NaOH are used with 500. g of water,
  what is the molality (m) of the solution?

5
Calculating Molarity

• 1) 4.0 g NaOH x 1 mole NaOH 0.10 mole NaOH
• 40.0 g NaOH
• 2) 500. g x 1 kg _ 0.500 kg
  water
• 1000 g
• 3. 0.10 mole NaOH 0.20 mole NaOH
• 0.500 kg water 1 kg water
• 0.20 m NaOH

6
Calculating Molality

• A KOH solution contains 400. g water and 2 mole
  KOH. What is the molality of the solution?
• 1) 8 m
• 2) 5 m
• 3) 2 m

Drano
7
Solution

• 2) 5 m
• M 2 mole KOH 5 m
• 0.4 kg water

Drano
8
Calculating Molarity

• A glucose solution is made with 2.0 kg water and
  72 g glucose (C6H12O6). If glucose has a molar
  mass of 180. g/mole, what is the molality of the
  glucose solution?
• 1) 0.20 m
• 2) 5.0 m
• 3) 36 m

9
Solution

• A glucose solution is made with 2.0 kg water and
  72 g glucose (C6H12O6). If glucose has a molar
  mass of 180. g/mole, what is the molality of the
  glucose solution?
• 1) 72 g x 1 mole x 1 0.20 m
  
• 180. g 2.0 kg

10
Molality Grams Volume

• What is the molality of a solution prepared by
  mixing 3.0 moles NaOH with sufficient solvent to
  make a total mass of 400 g?
• 1) 12 m
• 2) 10.7 m
• 3) 300 m

11
Solution

• 2) 3.0 mol x 40 g 120 g solute
• 1 mol
• mass of solvent 400 g total 120 g solute
  280 g solvent
• m 3.0 mol
• 0.280 kg
• m 10.7 m