Solutions

Homogeneous mixture = solution

Solutethe substance that’s being dissolved

Solvent - the substance that the solute is dissolved in.

Types

Gas/gas

Gas/liquid

Liquid/liquid

Solid/liquid

Air is 78% N2 and 21% O2

Carbonated sodas are made by dissolving CO2 gas in water

Vinegar is 5% acetic acid, 95% water

Sports drinks are 0.1% NaCl, 5% sugar and 94.9% water.

Examples

Which one is the solventand which one is the solute?

How much will dissolve?

Saturated solution: No more solute will dissolve.

Unsaturated solution: Haven’t added enough solute to the solvent for the solution to be saturated. If more solute is added, it will dissolve.

Supersaturated solution: Have ‘tricked’ the solution so that there is more solute dissolved in the solvent than is present in a saturated solution. Adding more solute causes the excess solute to precipitate out of solution.

Solubility curves

Plots the MAXIMUM

number of grams of

a solute that will

dissolve in 100 g of

the solvent at

particular

temperatures.

2. Is a solution containing 80 g of NH4Cl at 80o C saturated, unsaturated or supersaturated?

1. Is NaNO3 or KNO3 more soluble at 50o C?

4. Is a solution containing 80 g of KNO3 at 80o C saturated, unsaturated or supersaturated?

Ce2(SO4)3

3. What is least soluble at 40oC?

5. At what temp. will crystals appear for the solution in #4?

50oC

Temperature effects

If the solute is a liquid or a solid, solubility increases as temperature increases.

TemperatureSolubility

as

Solubility of gases

•As the TEMPERATURE INCREASES, the SOLUBILITY of the gas DECREASES.

This is because the intermolecular forces between the gaseous solute and the solvent decrease with increased thermal motion.

•As the PRESSURE of the gas ABOVE THE SOLVENT INCREASES, the SOLUBILITY of the gas INCREASES.

The relationship between pressure and gas solubility is given by Henry’s Law (yes, another named gas law )

2

2

1

1PS

PS

Solution concentration calculations

Mass% (m/m) = 100solvent) of masssolute of (mass

solute of mass

Example: What is the m/m% of NaCl if 5 g of NaCl is dissolved in 95 g of water?5% by mass

100solvent) of volume solute of (volume

solute of volume Volume% (v/v) =

Example: What is the v/v% if 20 mL of ethanol is dissolved into 80 mL of water?20% by volume

Mass/Volume% (m/v) = 100solvent of volumesolute of mass

Example: What is the m/v% if 15 g of NaCl is dissolved into 100 mL of water?15% mass/volume

Mole Fraction: If substance A is the solute and substance B is the solvent, the concentration of both can be expressed in terms of their relative number of moles.

BA

AA nn

nX

BA

BB nn

nX

Example: A solution of hydrochloric acid contains 1.03 mol HCl and 3.47 mol water. What is the mole fraction for both substances?

0.229OH mol 3.47HCl mol 1.03

HCl mol 1.03nn

nX

2H2OHCl

HClHCl

0.771OH mol 3.47HCl mol 1.03

OH mol 3.47nn

nX

2

2

H2OHCl

H2OH2O

Molarity =solvent of literssolute of moles

Example 1: What is the molarity of a solution prepared by dissolving 1.5 mol NaOH in 500 mL of water?

M 3.0OH L 0.500

NaOH mol 1.5

2

Example 2: How could 1.5 L of a 2.5 M solution of NaCl be prepared?

Step 1: Calculate how many moles of NaCl are needed

M = n/V n = MV n = (2.5 M)(1.5 L)

n = 3.75 moles of NaCl

Step 2: Calculate the weight of 3.75 mol NaCl

M =Vn

3.75 mol NaCl x 58.443 g/mol NaCl = 219.16 g NaCl

Solution Dilution

Concentrated hydrochloric acid is 12 M. How could 1.5 L of 2.5 M HCl be prepared?

The key principle behind the ‘magic equation’ for dilution is that the number of moles of HCl is conserved…we’re just increasing the amount of water.

M1V1 = M2V2

M1 = 12 MV1 = ?

M2 = 2.5 MV2 = 1.5 L

(12 M)V1 = (2.5 M)(1.5 L)

V1 = 0.313 L

Ans: Dissolve 0.313 L of concentrated HCl in 1.187 L of water to give a total volume of 1.5 L of 2.5 M HCl.

Definitions:

Electrolytes: solutions in which the solutes are ions. Electrolyte solutions will conduct electricity.

Nonelectrolytes: solutions in which the solutes are molecules and NOT ions. Nonelectrolytes will NOT conduct electricity.