standard 6: solutions chapter 16

Standard 6: Solutionschapter 16

ChemistryMs. Siddall

Standard 6a: solution definitions• Solution: a homogeneous mixture of 2 or

more substances in the same physical state.

• Properties:

– Particles are small

– Particles are evenly mixed

– Particles will not separate• Examples:

– air (nitrogen & oxygen)

– Gatorade (water, sugar, etc)

– NaCl(aq) (salt & water)

Summary 1

• Is muddy water a solution? Why/why not?

• Solute: substance that is dissolved e.x. sugar

• Solvent: does the dissolving e.x. water

• Concentration: The amount of solute in a given amount of solvent e.x. [HCl]

• (aq) = aqueous = A solution where water is the solvent

Summary 2

Consider lemonade.

1. What is the solvent?

2. What are the solutes?

• Solvent: H2O molecules with dipole

• Solute: Ionic crystal lattice

Standard 6b: Dissolving Process

+

-

+

+

++

++

+

-

-

-

-

-

• Polar H2O molecules surround positive and negative ions and break apart crystal lattice

• Water molecules move away (diffusion) so the process is repeated

Show animation

Summary 3

Explain how water dissolves ionic compounds

• It takes energy to break bonds

NaCl(s)

NaCl(aq)en

erg

y

Energy needed to overcome

lattice energyEnergy

released during

dissolvingDissolving

Summary 4

Does the energy diagram for dissolving NaCl represent anendothermic or exothermic process? Explain your answer.

Saturated solution: A solvent can not dissolve any more solute

• A saturated solution is at equilibrium. Particles are dissolving and precipitating at the same rateNaCl(s) Na+

(aq) + Cl-(aq)

Summary 5

Does the dissolving process stop at equilibrium? Explain why/why not.

• Some factors affect solubility (how much solute is dissolved)

• Some factors affect rate (how fast solute is dissolved)

• Some factors affect rate and solubility

Standard 6c: Factors that affect the dissolving process

Standard 6c: Factors that affect the dissolving process

Factors affecting how much solute is dissolved

1. Type of solvent / solute

• Polar solvents dissolve polar & ionic solutes

• Non-polar solvents dissolve non-polar & covalent solutes

e.x oil and water do not mix

Summary 6

Is oil a polar compound or a non polar compound? How do you know?

2. Temperature• For solids: Temperature solubility

Temperature increases kinetic energy of solvent particles therefore more solute can be dissolved

• For gases: Temperature solubility Temperature increases the kinetic energy of solute particles therefore more particles escape from solution

Summary 7

Why does the solubility of gas in solution decrease with increasing temperature?

Solubility of solids & gases

3. Pressure (Gasses Only!)

• Increasing pressure forces more gas into solution

• Pressure solubility • Pressure solubility

High pressure

low pressure

solution

air

Gas

Summary 8

Does the concentration of carbon dioxide in your soda increase or decrease when you open the bottle? Why?

Factors that affect the rate of solubility (how quickly something dissolves)

1. Temperature:

• T rate • T rate • Increasing temperature increases kinetic

energy = increased motion = increased diffusion

2. Surface Area (particle size):

• S.A. (particle size ) rate • S.A. (particle size ) rate • Increasing surface area increases

opportunity for interaction between solute and solvent

3. Stirring:

• stirring rate • stirring rate • Stirring increases particle motion so more

particles can be dissolved at the surface of the solid

Summary 9

1. Name one factor that affects only solubility

2.Name one factor that affects only rate

3.Name one factor that affects rate and solubility

Standard 6d: calculations• Molarity (mol/L)Molarity = Moles solute Liters solution • Grams per Liter (g/L)

= Grams solute

Liters solution

• Percent Composition (%)

grams solute x 100%

grams solution• Parts Per Million (ppm)

grams solute x 106

grams solution

Summary 10

A solution contains 80g of NaOH in 500ml of solution. Calculate:

1.‘grams per liter’2. Molarity3. percent composition for the solution

• Using ‘Parts per Million’ (ppm)• Usually used to measure solutions

containing a small amount of solute • e.x air quality or drinking water quality

– Air contains about 1ppm CO2 (Every 1million grams of air contains 1g CO2)

• smaller concentrations are measured in ppb(parts per billion)– Drinking water usually contains ≤ 0.5 ppb lead

Summary 11

Which solution has the highest concentration of fluoride ions?a) 10 ppm F-

b) 100 ppm F-

c) 10 ppb F-

d) 100 ppb F-

• Example: What is the concentration (ppm) of a 1L solution containing 5mg arsenic?

(The density of aqueous solutions = 1g/ml)

Standard 6e: effect of solute on freezing and boiling point.

Molality (m) = moles solute Kg

solvent

e.x. what is the molality of a solution made by dissolving 180g sugar (C6H12O6) in 500g water?

180g sugar

500g water 180g sugar

1 mol sugar 1000g

1 kg= 2m

Summary 18

what is the molality of a solution made by dissolving 92g ethanol (C2H6O) in 200g water?

92g ethanol

200g water 46g ethanol

1 mol ethanol 1000g

1 kg= 20m

Freezing point depression and boiling point elevation: adding solute to a solvent lowers the freezing point and raises the boiling point of the solvent.

• Solute particles disrupt crystallization and evaporation.

• The change in freezing point or boiling point is directly proportional to the molality of solute particles.

• A solute that produces more ions in solution has the greatest effect.

Summary 19

Explain why it takes more energy to boil water when it has more solute particles dissolved in solution.

3m sugar

3 moles NaCl produces 6m of solute particles

3moles CaCl2 produces 9m of solute particles

Summary 19

Which will affect the boiling point of solution more? WHY?

a) 1m NaClb) 1m CaCl2c) 1m AlCl3

6f: Chromatography and distillation.

Chromatography: the separation of solution into individual substances using differences in polarity.

e.x. DNA analysis

Distillation: separation of solutions into individual substances using differences in physical properties (boiling point)

e.x. salt water can be purified by distillation

Summary 20

Why is it possible to separate alcohols by distillation?