8.2 Solubility and Concentration

Key Concepts

• How are solutions with different amounts of solute described?

• What factors determine the solubility of a solute?

• What are three ways to measure the concentration of a solution?

Solubility

• The _______________ amount of solute that dissolves in a given amount of solvent at a constant temperature is called _______________

• Solubilities are usually expressed in _______ of solute per 100 grams of ____________

maximum

solubility

gramssolvent

At a given temperature, different substances have different solubilities in water.

Which compound is the most soluble in water at 20°C

Table sugar

Unsaturated Versus Saturated• If the amount of solute dissolved is _______

than the maximum that could be dissolved, the solution is called an ______________ solution

– Ex: Earth’s oceans contain _______ dissolved salt than they can hold

less

unsaturated

less

• A solution that holds the ____________ amount of solute per amount of solution under the given conditions is called a ______________ solution– Ex: The Dea Sea has a salinity of ______ salt

compared to only about ______ percent for ocean water

• _______________ solutions contain ________ solute than the usual maximum amount and are typically _____________– Ex: While making fudge, you heat a highly concentrated mixture of sugar, chocolate and a water-based solvent to a _________ enough temperature to make a

__________ solution that is supersaturated

maximum

saturated25%

3.5

Supersaturated more

unstable

highsugar

Like Dissolves Like

• Water can dissolve an enormous variety of substances, but it does ______ dissolve everything

• The phrase that scientists often use when predicting solubility is _____________________

• This phrase means that dissolving occurs anytime a solute and solvent have ______________ in polarity

NOT

“like dissolves like”

similarities

Practice Solubility Questions!• Can water dissolve other polar molecules?

• Can water dissolve other compounds that are similar to it in structure and hydrogen bonding?

• Can water dissolve a nonpolar molecule like oil?

• Can oil dissolve other nonpolar molecules?

Yes…both are polar

Yes…similar structure and bonding

No…not similar or “unlike”

Yes….both are nonpolar

Special Topic: Soap

• Soap has unique propertiesbecause one end of the moleculeis ____________ and the otherend is _____________

• The polar end attracts ____________ and the nonpolar end attracts ___________

• Basically, the nonpolar end ____________ the oil and the polar end interacts with water to ____________ the oil away

polar

nonpolar

wateroil

dissolves

rinse

Effect of Temperature on Solubility

• The solubility of most __________ solutes _____________ with an increase in temperature

• What is being plotted on the x-axis?

• What is being plotted on the y-axis?

solidincrease

temperature

Grams of solute

• At 20°C, how many grams ofNaNO3 are dissolved?

• At 50°C, how many grams ofNaNO3 are dissolved?

• If 130 grams of NaNO3 were dissolved at 50°C, what kind of solution would it be?

• If 80 grams of NaNO3 were dissolved at 50°C, what kind of solution would it be?

83 g

112 g

supersaturated

unsaturated

Solubility of Gases

• The solubility of a _________ in a liquid actually ______________ with increases in temperature

• Due to this many fish must live in _______ water so that the concentration of dissolved ____________ remains high

• Think of soda in a bottle…does it taste

more carbonated (bubbly) when it is cold

or hot?

gasdecreases

cold

oxygen

Cold…contains more CO2

• Pressure also affects the solubility of a gas…

• Increasing pressure allows ________ carbon dioxide to dissolve in a liquid

• Think of soda in a bottle again…is it more carbonated with or without the cap on?

more

With the cap…more pressure

Molarity• Suppose you are hospital or pharmacy worker,

and you need to make a salt solution that matches the salt concentration of a _____________ blood

• Blood is a ___________ solution, but this term gives only __________________ information

•You will need to measure things accurately using numbers or _________________ information

patient’s

dilute

qualitative

quantitative

• Concentration units can ________ greatly.

• For chemistry applications, the concentration term ____________ is generally the most useful

• Molarity, symbolized with an ______, is defined as the number of _________ of solute per __________ of solution

Molarity = _moles of solute_ liter of solution

• Notice that the ______________ in liters is the total volume for the _____________

vary

molarity

Mmoles

liter

volumesolution

• Concentration can also be expressed as percent by _____________– Example: Fruit juice labels

– What percentage of cranberrry

juice is found in the product

shown?

volume

27%

Percent by Mass

Concentration expressed as a percent by ___________ is more useful when the solute is a solid.

Concentration of Solutions

mass

Review Question 1

• Explain the difference between an unsaturated, saturated, and supersaturated solution

Contains less than the max.amount of dissolvedsolute Contains more

than the max.amount of dissolvedsolute

Contains themax. amountof dissolved solute

Review Question 2

• How does temperature affect solubility for most solid solutes?

• And for gases dissolved in a liquid?

As temp. increases, so does solubility

As temp. increases, solubility decreases

Review Question 3

• What is the equation for molarity?

M = _moles of solute_ liter of solution