II III I C. Johannesson I. The Nature of Solutions Ch. 14 - Solutions.

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C. Johannesson

I. The Nature of SolutionsI. The Nature of Solutions

Ch. 14 - SolutionsCh. 14 - Solutions

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Definitions Definitions

Solution - Solution - homogeneous mixture

Solvent Solvent - present in greater amount

Solute Solute - substance being dissolved

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Definitions Definitions

Solute Solute - KMnO4 Solvent Solvent - H2O

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Solvation Solvation

Solvation – Solvation – the process of dissolving

solute particles are separated and pulled into solution

solute particles are surrounded by solvent particles

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SolvationSolvation

StrongElectrolyte

Non-Electrolyte

solute exists asions only

- +

salt

- +

sugar

solute exists asmolecules

only

- +

acetic acid

WeakElectrolyte

solute exists asions and

molecules DISSOCIATION IONIZATION

View animation online.

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Solvation Solvation

NONPOLAR

NONPOLAR

POLAR

POLAR

““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”

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Solvation Solvation

Soap/DetergentSoap/Detergent• polar “head” with long nonpolar “tail”• dissolves nonpolar grease in polar water

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Solubility Solubility

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

concentration

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Solubility Solubility

SolubilitySolubility• maximum grams of solute that will

dissolve in 100 g of solvent at a given temperature

• varies with temp• based on a saturated soln

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Solubility Solubility

Solubility CurveSolubility Curve• shows the

dependence of solubility on temperature

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Solubility Solubility

Solids are more soluble at...Solids are more soluble at...• high temperatures.

Gases are more soluble at...Gases are more soluble at...• low temperatures &• high pressures

(Henry’s Law).• EX: nitrogen narcosis,

the “bends,” soda

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II. ConcentrationII. Concentration

Ch. 14 - SolutionsCh. 14 - Solutions

C. Johannesson

ConcentrationConcentration

The amount of solute in a solution.

Describing Concentration

• % by mass - medicated creams

• % by volume - rubbing alcohol

• ppm, ppb - water contaminants

• molarity - used by chemists

• molality - used by chemists

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MolarityMolarity

Liters

moles(M)molarity

Must be in liters

1000 mL = 1 L L 1

mol0.25 0.25M

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MolalityMolality

solvent ofkg

solute of moles(m)molality

mass of solvent only

1 kg water = 1 L waterkg 1

mol0.25 0.25m

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2211 VMVM

Dilution Dilution

Preparation of a desired solution by adding water to a concentrate.

Moles of solute remain the same.

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Preparing Solutions Preparing Solutions

500 mL of 1.54M NaCl

500 mLwater

45.0 gNaCl

• mass 45.0 g of NaCl• add water until total

volume is 500 mL• mass 45.0 g of NaCl• add 0.500 kg of water

500 mLmark

500 mLvolumetric

flask

1.54m NaCl in 0.500 kg of water

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Preparing Solutions Preparing Solutions

Copyright © 1995-1996 NT Curriculum Project, UW-Madison(above: “Filling the volumetric flask”)

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Preparing Solutions Preparing Solutions

Copyright © 1995-1996 NT Curriculum Project, UW-Madison(above: “Using your hand as a stopper”)

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Preparing Solutions Preparing Solutions

250 mL of 6.0M HNO3 by dilution

• measure 95 mL of 15.8M HNO3

95 mL of15.8M HNO3

water for

safety

250 mL mark

• combine with water until total volume is 250 mL

• Safety: “Do as you oughtta, add the acid to the watta!”

C. Johannesson

Solution Preparation LabSolution Preparation Lab

Turn in one paper per team. Complete the following steps:

A) Show the necessary calculations.

B) Write out directions for preparing the solution.

C) Prepare the solution. For each of the following solutions:

1) 100.0 mL of 0.50M NaCl

2) 0.25m NaCl in 100.0 mL of water

3) 100.0 mL of 3.0M HCl from 12.1M concentrate.

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III. Colligative Properties

III. Colligative Properties

Ch. 14 - SolutionsCh. 14 - Solutions

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Definition Definition

Colligative PropertyColligative Property

• property that depends on the

concentration of solute particles, not

their identity

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Types Types

Freezing Point DepressionFreezing Point Depression (tf)

• f.p. of a solution is lower than f.p. of the pure solvent

Boiling Point ElevationBoiling Point Elevation (tb)

• b.p. of a solution is higher than b.p. of the pure solvent

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Types Types

View Flash animation.

Freezing Point Depression

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Types Types

Solute particles weaken IMF in the solvent.

Boiling Point Elevation

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Types Types

Applications• salting icy roads• making ice cream• antifreeze

• cars (-64°C to 136°C)• fish & insects

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Calculations Calculations

t: change in temperature (°C)

k: constant based on the solvent (°C·kg/mol)

m: molality (m)

n:# of particles

t = k · m · n

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Calculations Calculations

# of Particles# of Particles

• Nonelectrolytes (covalent)• remain intact when dissolved • 1 particle

• Electrolytes (ionic)• dissociate into ions when dissolved• 2 or more particles

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Calculations Calculations

At what temperature will a solution that is composed of 0.73 moles of glucose in 225 g of phenol boil?

m = 3.2mn = 1tb = kb · m · n

WORK:

m = 0.73mol ÷ 0.225kg

GIVEN:b.p. = ?tb = ?

kb = 3.60°C·kg/moltb = (3.60°C·kg/mol)(3.2m)(1)

tb = 12°C

b.p. = 181.8°C + 12°C

b.p. = 194°C

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Calculations Calculations

Find the freezing point of a saturated solution of NaCl containing 28 g NaCl in 100. mL water.

m = 4.8m

n = 2

tf = kf · m · n

WORK:

m = 0.48mol ÷ 0.100kg

GIVEN:

f.p. = ?

tf = ?

kf = 1.86°C·kg/mol

tf = (1.86°C·kg/mol)(4.8m)(2)

tf = 18°C

f.p. = 0.00°C - 18°C

f.p. = -18°C