SolutionsChemistry, Ch. 13, pg 454-486

Today’s Learning Objectives

1. Know the vocabulary of solutions.

2. Learn to calculate parts per million

3. Learn to calculate molarity

4. Use molarity in BBTT

5. Learn to calculate molality.

What is a Solution? (13-1)

Solution – a homogenous mixture, usually a liquid

Which of these is a solution?

What is a Solution?

2 parts to a solution:

1. Solvent – the substance doing the dissolving

2. Solute – the substance being dissolved

Essentially, whichever one there is more of, is the solvent

Could there be more than one solute?

Concentration & Molarity (13-2)

Would Kool-aid taste the same if you used 2 cups of sugar instead of one?

Concentration – the amount of a particular substance in a given quantity of solution

Symbolized with brackets []

I.e. the concentration of H+ = [H +]

Concentration & Molarity

Dilute – relatively small amount of solute in solution

Concentrated – relatively large amount of solute in solution

Concentration & Molarity

Three ways to measure concentration

1. Parts per million (ppm)

2. Molarity (M)

3. Molality (m)

Concentration & Molarity

Parts per million – the number of grams solute per 1,000,000 g solution

Often used in pollution, air quality, water quality – places where extremely small concentrations are important

Just like a percent, but per million instead of per hundred

000,000,1solution g

solute gppm

Concentration & Molarity

Example:

There are 2.2 mg of lead in exactly 500 g of a water sample. How many ppm are there?

4.4 ppm

Concentration & Molarity

Molarity (M) – the concentration of a solution expressed in moles of solute per liter of solution

Measurement used most often in general chemistry labs

solution L

solute mol Molarity

L

mol M

Concentration of Solutions

As you might guess, we’ll be using that formula…

Also molarity makes for great BBTT!

Use it as a conversion factor between volume (L) and moles

Probs…

Problem Type 1: Calculate Molarity

What is the molarity of a 3.50 L solution that contains 90.0 g of NaCl?

Answer: 0.440 M NaCl

Probs…

Problem Type 2: Calculate part of the molarity formula (mol or L)

How many moles of HCl in 0.8 L of a 0.5 M HCl solution?

Answer = 0.4 mol HCl

Probs…

Problem Type 3: Use molarity in BBTT

If you have 2.1 g of KCl available, how many liters of a 0.55 M KCl solution can you make?

Answer: 0.051 L (51 mL)

Molality

Molality (m) – The concentration of a solution expressed

in moles of solute per kg of solvent

Used when studying solutions with temperature changes, molality doesn’t change with temp, molarity can

solventkg

solutemolmmolality )(

Molality problem

A solution of I2 in CCl4 is used when iodine is needed for certain chemical tests. How much I2 must be added to prepare a 0.480 m solution of iodine in CCl4 using 100.0 g of CCl4?

0.0480 mol or 12.2 g I2

Application

Form lab groups of 3

Each group calculates the number of grams needed to make a 0.500 L of a 0.100 M solution of CuSO4·5H2O.

Then each group mixes it according to the procedure on page 463 in text.

Goggles & Aprons, please.

Each group at a different lab table.

Solubility & Dissolving (13-3)

Today’s Learning Objectives:

Understand why some combinations of chemicals dissolve and others do not.

Know factors speeding the rate of dissolution.

Be able to use the terms of solubility.

Use a solubility chart.

Solubility & Dissolving

What happens when you mix grease and water? Sand and water? Sugar and water?

Why do some things dissolve when others do not?

Solubility & Dissolving

Solubility – the ability of a substance to dissolve into another

General rule: “Like Dissolves Like”

link

Solubility & Dissolving

Vitamin example:

Vitamin C has a shape with little –OH groups attached to it

The –OH groups are polar and participate in hydrogen bonding

So Vitamin C is soluble in water

Solubility & Dissolving

Vitamin A also has an –OH group, but it contains a long chain of carbons

Long chains of carbons tend to behave as if nonpolar and certainly don’t participate in hydrogen-bonding

Consequently the molecule (over all) is not soluble in water

Solubility & Dissolving

Vitamin C is water soluble Vitamin A is fat soluble

Solubility & Dissolving

Other terms:

Miscible – two or more liquids that can dissolve into each other in any proportion

Ex. ethyl alcohol and water

Immiscible – two liquids that can not dissolve into each other at all

Ex. oil and water

Solubility & Dissolving

Most solids fall between miscible and immiscible

There is a limit to how much sugar will dissolve in a given amount of water

Text notes that even a tiny amount of glass will dissolve into water!

Solubility & Dissolving

Factors speeding the rate of dissolution Increasing the surface area of the solute

Molecularly speaking… the larger surface area allows for more interaction between the solvent and solute particles

Stirring or shaking the solution

Molecularly speaking… Moving the solvent around brings less-concentrated solution close to solute and it diffuses faster

Heating the solvent

Molecularly speaking… Speed the molecules up, and they collide at higher speeds

Solubility & Dissolving

At some point, no more solute can be dissolved in a solution Saturated solution – A solution that contains the

maximum amount of dissolved solute

Unsaturated solution – A solution that contains less

solute than a saturated solution at the same temp

Supersaturated solution – A solution that contains

more dissolved solute than a saturated solution at that temp

Formed by cooling a saturated solution

Solubility Rules: Determined by

experiment

Solubility Chart: Blank = no combos precipitate (ppt). Shaded = all combos

precipitate.

Where certain ions will precipitate, but others will not, notes are written that indicate

what will happen.

Physical Prop. Of Solutions (13-4)

Today’s Learning Objectives:

Know what an electrolyte is.

Explain and predict colligative properties.

Physical Prop. Of Solutions

The properties of a solvent change when solutes are added

Examples:

Conductivity

Freezing point / boiling point

Physical Properties Of Solutions

Electrolyte – a substance that dissolves in a solvent and makes it conduct electricity

Ex. all salts, acids

Pure water does not conduct electricity

Tap water, lake water, and ocean water do…

Physical Properties Of Solutions

Colligative property – property of a substance that is determined by the number of particles present, yet independent of the identity of the particles

2 Colligative properties:

Boiling-point elevation

Freezing-point depression

Physical Properties Of Solutions

Adding any solute to water will raise the boiling point of water

Physical Properties Of Solutions

Adding any solute to water will lower the freezing point of water (link)