Solutions

Definitions

• Solution – Homogeneous mixture of two or more substances

• Solute – Substance that is dissolved

• Solvent – Substance that dissolves the solute

• Aqueous Solution – water is the solvent

Example: NaCl(aq) = NaCl + H2O

(solute) (solvent)

Concentration

• Concentration - Quantity of solute in a given measure (volume or mass) of solution

• Concentration can be expressed as: – Molarity (M)– Percent Composition/Percent Mass– Parts per million (ppm)

Molarity

• Number of moles of solute in one liter of solution

M = moles of solute

liters of solution

Examples:• 1.0L of 6.0M HCl contains 6.0 moles of HCl• 1.0L of 1.0M HCl contains 1.0 mole of HCl

Molarity Examples

1. What is the molarity of a solution that contains 1.0 mole of solute in 5.0L of solution?

2. What is the molarity of a solution that contains 2.5 moles of NaCl in 3500mL of solution?

3. What is the molarity of a solution that contains 50.0g of AgNO3 in 2.0L of water?

4. How many grams of H2SO4 are present in 5.0L of 3.0M H2SO4?

Percent Composition/Percent Mass

= mass of part x 100

mass of whole

Percent Composition Examples

1. If 5.0g of a 200.g sample is aluminum, what is the percent mass of aluminum?

2. 10.0g of NaCl is dissolved in 150.g of water. What is the percent mass of NaCl in the solution?

3. If 23% of a 58.5g sample is calcium, how many grams of calcium are in the sample?

Parts per million (ppm)

= grams of solute x 1,000,000

grams of solution

ppm Examples

1. Calculate the concentration (in ppm) if 0.010g of NaCl is dissolved in 750g of solution.

2. Calculate the concentration (in ppm) if 1.25g of CuSO4 is dissolved in 550g of water.

3. How much Fe is in a 5000.g solution, if it has an iron concentration of 500.ppm?

Dilution

M1V1 = M2V2

M = Molarity

V = Volume

Dilution Examples

1. How many milliliters of 12M HCl must be added to water to make a 300.0mL solution of 6.0M HCl?

2. How many milliliters of 18M H2SO4 must be used to make a 1.0L sample of 1.0M H2SO4?

3. 15mL of 3.0M NaOH are diluted to a volume of 500.mL. What is the resulting concentration of the diluted solution?

Warm - up

1. 250mL of 3.0M NaOH is diluted to 0.10M. What is the volume of the diluted solution?

2. How many grams of KCl are required to make 500.mL of a 1.25M solution?

Solubility

Depends on:

1. The nature of the solute and solvent– “Like dissolves Like”

• Polar solvents dissolve polar and ionic solutes

• Nonpolar solvents dissolve nonpolar solutes

Solubility

2. Temperature• For solids, solubility increases as

temperature increases• For gases, solubility increases as

temperature decreases

3. Pressure• Gases are more soluble at higher pressures

Factors that influence the rate of dissolving

1. Size of the particles• More surface area (smaller

pieces) = faster

2. Stirring

3. Amount of solute already dissolved

4. Temperature

Saturated Solutions

• Contain the exact amount of solute that can be dissolved at a certain temperature and pressure

• Solute is added under constant conditions until no more will dissolve

• If additional solute is added it will not dissolve

Unsaturated Solutions

• Contain less solute then can be dissolved at a certain temperature and pressure

• If additional solute is added it will dissolve

Supersaturated Solutions

• Contains more solute then should be dissolved (more than the saturated solution)

• A saturated solution is made at a high temperature and allowed to gradually cool

• Very rare, very unstable

• If additional solute is added the “extra” solute will fall out of solution (re-crystallize)

Solubility Curves – Table G

• Saturated Solution– on the line

• Unsaturated Solution– below the line

• Supersaturated Solution– above the line

Examples

1. 60g of NH4Cl is dissolved in 100g of water at 70oC. What type of solution is this?

2. How many grams of NaCl must be dissolved in 100g of water at 40oC to make a saturated solution?

Examples

3. How many grams of KNO3 must be dissolved in 200g of water at 55oC to make a saturated solution?

4. A solution contains 25g of KCl in 100g of water at 50oC. How much additional KCl must be added to make a saturated solution?

Table F – Solubility Guidelines

• Explains if a combination of ions will be soluble or insoluble in water

Table F Examples

• Indicate if the following are soluble or insoluble

1. LiNO3

2. Li3PO4

3. NaOH

4. Al(OH)3

5. MgCO3

Colligative Properties

• Properties that depend on the number of particles in solution

Examples: Boiling Point, Freezing Point, Vapor Pressure

Boiling Point / Freezing Point• The addition of a solute to a solvent

causes the– Boiling point to increase– Freezing point to decrease

• The great the concentration of particles the greater the effect

Example: The addition of antifreeze (ethylene glycol) to your radiator increases the boiling point and decreases the freezing point

Boiling Point

• The addition of a solute raises the boiling point of the solvent

• One mole of particles raises the boiling point of water by 0.52oC

Freezing Point

• The addition of a solute lowers the freezing point of the solvent

• One mole of particles lowers the freezing point of water by 1.86oC

Electrolytes / Nonelectrolytes• Electrolytes dissociate (break apart) in

solution– Ionic Compounds, Acids, BasesEx: NaCl in water breaks apart into Na+ and Cl- ion

NaCl Na+ + Cl-

• Nonelectrolytes do not dissociate in solution– Molecular substances

Ex: sugar in water

C6H12O6 C6H12O6

H2O

H2O

Dissociation Factor

• How many particles (ions) the molecule dissociates into

Examples:

1. NaCl Na+ + Cl- (df = 2)

2. CaCl2 (df = )

3. C6H12O6 (df = )

Examples

1. Equal amounts of which will lower the freezing point of water more?

a. Sugar (C6H12O6)

b. Salt (NaCl)

2. Explain why

NaCl breaks into 2 particles (df = 2), sugar does not break apart (df = 1)

Examples

3. Which would have a lower freezing point, 3.0M CaCl2(aq) or 3.0M NaCl(aq)? Explain why.

4. Which will have a higher boiling point,6.0M HCl or 3.0M HCl? Explain why.

5. Which would have a lower freezing point, 6.0M HCl or 3.0M HCl? Expain why.