Unit: Chemical InteractionsChapter 8: Solutions

When substances dissolve to form solutions, the properties of the mixture change.

8.1: A solution is a type of mixture8.2: The amount of solute that dissolves

can vary8.3: Solutions can be acidic, basic, or

neutral8.4: Metal alloys are solid mixtures

Review / warm-up What are their chemical formulas? What are the elements? Which is an ionic compound and which is a covalent

compound? Are the properties of each compound the same/different than

the atoms/elements that form them? What is the different in how these compounds are held

together?

8.1: A solution is a type of mixture

Na Cl O

CO

animation

8.1 A solution is a type of mixture

8.1: A solution is a type of mixture

The parts of a solution are mixed evenly Mixture: a combination of substances – ex: fruit salad, chili

Can physically separate ingredients because they are not chemically changed – still the same substances

If a mixture is so completely blended together… The ingredients canNOT be separated and identified as different

substances Solution: a type of mixture, called a homogeneous mixture

“same throughout” (“well-mixed”) All portions of the the mixture have the same properties

Sand + Water Sand sinks to the bottom ; Solution? Sugar + water sugar is dispersed throughout; Solution? Other common solutions: seawater, gasoline, liquid part of blood

8.1: A solution is a type of mixture

Solutes and Solvents – components of a solution Solutions – have a definite composition Solute – a substance that is dissolved to make a solution

When it dissolves, it separates into individual particles It is dissolved into the…

Solvent – a substances that dissolves a solute Most common: water Others – ex: turpentine, soaps - to remove oils

After the solute dissolves and separates into individual particles, it is not possible to identify the solute and solvent as different substances

Ex:

8.1: A solution is a type of mixture

Solution Solute solventSalt waterblood

salt

waterCalcium ions, sugar

water

8.1: A solution is a type of mixture

Solvent (water)

animation

Solute

(salt)

A salt water solution

Types of Solutions Gas Solution:

Ex: air = oxygen (an other gases) dissolved in nitrogen Liquid Solution:

Ex: vinegar = acetic acid dissolved in water Solid Solution:

Ex: bronze = tin dissolved in copper Must first be melted to a liquid, then mixed, then cooled to solid

Mixed? Ex: soda = carbon dioxide dissolved in water solution Ex: saltwater = salt dissolving in water

8.1: A solution is a type of mixture

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tion

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etsolute

solvent

solutesolutesolutesolutesolutesolutesolute

solventsolventsolventsolventsolventsolventsolvent

Suspensions Suspension: the particles added are larger than

those found in a solution, so instead of dissolving, these larger particles turn the liquid cloudy Ex: Flour added to water Can sometimes separate the components of the

suspension using a filter

8.1: A solution is a type of mixture

Solvent and solute particles interact The parts of a solution are not changed into new

substances The solute and the solvent can still be physically

separated, though they do interact Ex: a solid dissolves in a liquid, the particles of the

solute are surrounded by particles of the liquid (solvent) The solute particles become evenly distributed through

the solvent

8.1: A solution is a type of mixture

Solvent and solute particles interact (2)

The way a solid compound dissolves in a liquid depends on the type of bonds in the compound

Ionic compounds split apart into individual ions Ex: table salt dissolves in

water – the sodium and chloride ions separate, and each ion is surrounded by water molecules

Covalent compounds dissolved in water, the molecules stay together and are surrounded by solvent molecules Ex: table sugar dissolves in

water – C12H22O11 stays as such

8.1: A solution is a type of mixture

Properties of solvents change in solutions Solutes change the physical properties of a

solvent in every solution A solution’s physical properties differ from the

physical properties of the pure solvent Dependent on the amount of solute added

Lowering the Freezing Point Freezing Point: temperature Liquid Solid

A solvent’s freezing point is lowered when a solute is dissolved in it Ex: add salt to water – freezing point drops below 32oF (0oC)

Useful for snow and ice on sidewalks and roads (water freezes at a lower temperature, can help to melt ice)

• A limit: can get down to -6oF (-21oC) before the melted ice will freeze again

• Ice cream maker:• Canister surrounding ingredients holds a mixture of salt

and ice• The lower freezing point causes the ice to melt, absorbing

heat from surroundings• This includes the ice cream ingredients, which get

chilled• Then tiny ice crystals form all at once in the ice cream

mixture rather than a few crystals growing larger over time (as would happen in a regular freezer)

Raising the Boiling Point Boiling Point: temperature liquid gas

Boiling point of a solution is higher than the boiling point of the pure solvent Solution can remain a liquid at a higher temperature than its pure solvent

Ex: boiling point of water = 212oF (100oC) Salt raises the boiling point of water

Dependent on amount of salt added

Summary: a solute lowers the freezing point and raises the boiling point of the solvent in the solution Extends the temperature range in which the solvent remains a liquid

Uses: antifreeze in a car’s radiator (ethylene glycol added to water) Prevents the water from freezing in the winter Keeps it from boiling in the summer

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