Solutions

Pure Substances & Mixtureso What's the matter?o Pure Substances have a definite set of physical properties.

o (melting point, density, reactivity, etc)o Elements – cannot be broken downo Compounds – can be broken down

o Mixtures are two or more substances physically combined but not chemically combinedo Heterogeneous- a mixture that is not uniform throughout.

o Looks opaque – particles are large enough to block lighto Examples: dirt, chocolate chip cookies, milk, you

o Homogeneous- uniform throughouto Solution- a special homogeneous mixture where one substance is

dissolved into another. Almost always clear.o Examples: salt water (ionic compound + water), syrup, rubbing

alcohol

Everything! (har har)

MixturesActivity:• 1. Left-hand side of your notebook, draw 4 gas tanks and label them “H2 Gas,” “O2 Gas,”

“Hydrogen & Oxgen compound,” and “H2 & O2 Mixture.”• 2. Fill each tank with the appropriate molecules. Use open circles for hydrogen atoms and

filled-in circles for oxygen atoms.

H2 Gas O2 Gas O2 & H2

MixtureOyxgen & Hydrogen

Compound

PurePure

Pure Not pure

Not pure

Separating Mixtures Separating Mixtures:

distillation – using different boiling points to separate substances in a mixtureExamples: desalination

filtration – Using particle size to separate substances through a semi-permeable membrane.Examples: air filter in a car, tea bag, coffee filter

Chromatography- using a molecule’s ability to move through a medium. (demo)Examples: gel electrophoresis, HPLC

Solutions• Solutions have two components:

• Solvent – major component of a solution, dissolves the solute• Solute – minor component of a solution,dissolved by solvent

• The solute is the active ingredient of a solution.• Solutions used in chemical equations have (aq) added• aq = aqueous

• Steps of solution process: Known as solvation. (video)• Solute particles separate – energy is absorbed in order to

separate solute particles• Solvent molecules separate – energy also absorbed• Solvent particles surround solute particles – energy is released

• Solutions that release more energy than absorbed are called exothermic (energy EXiting).

• Solutions that absorb more energy than released are called endothermic (energy ENters)

SolubilitySolubility- able to be dissolved

Solids, liquids and gases can be dissolved.“Like dissolves Like”

Ionic & polar solutes dissolve in polar solvents.Non-polar solutes dissolve more in non-polar solvents.

• Immiscible - liquids that are not soluble in each other● Ex: Oil and water do not dissolve in each other because of

different polarities: Water is polar and oil is nonpolar

• Solubility

Not all ionic compounds are soluble in water Insoluble compounds will fall out of solution, forming a

precipitate Solubility for ionic compounds can be predicted using

solubility rules

Temperature & Pressure

Temperature and solubility•Solids dissolve better at higher temperatures

• Faster solvent particles allow solute particles more movement• Example: hot tea can dissolve more sugar than cold tea

•Gases do not dissolve well at higher temperatures• Gas molecules tend to disperse with higher temperatures• Example: soda bottle at room temperature will be less fizzy

than when coldPressure and solubility•Pressure has no effect on solid solutes•High pressure allows gases to dissolve better

• High pressure does not allow gas molecules to disperse easily• Example: sealed soda bottles stay fizzy longer

Saturation

Saturated solution- solution containing the maximum amount of solute for a specific amount of solvent at a given temperature and pressure.

More solute will not dissolve Unsaturated solution- does not contain the maximum amount of

solute in solution.More solute can dissolve until the maximum is reached

Supersaturated solution- an unstable solution that contains more solute than it can theoretically hold at a given temperature

Created by cooling a saturated solutionAdding more solute causes the excess solute to precipitate

• Precipitate- a solid that forms and settles down in a liquid mixture

Solubility Curves

• Solubility Curve– graph of solubility versus temperature

• compares the solubilities of multiple compounds in water as a function of temperature.

• solubility is expressed in terms of grams of solute per 100 grams of H2O.

Solubility Curves

How many grams of KNO3 can dissolve in 100 grams of water at 30ºC?Answer: About

48 grams.

Solubility Curves

How many grams of KClO3 can dissolve in 100 grams of water at 55ºC?Answer: About

25 grams.

Solubility Curves

How many grams of NH4Cl can be dissolved in 200 grams of water at 40ºC?Answer: About

96 grams.

Solubility Curves

A saturated solution of NaNO3 is prepared at 70ºC in 100 grams of water. If the temperature is lowered to 40ºC, how many grams of NaNO3 will precipitate?Answer: About

30 grams will precipitate out.

Solubility Curves

If 35 grams of NH4Cl are dissolved in 100 grams of water at 30ºC, is the solution unsaturated, saturated, or supersaturated?Answer: The

solution is unsaturated.