Properties of Solutions

A Solution is A homogeneous mixture The substances in the mixture are in the same physical state (solid, liquid, or gas)

Gas solution… Air is a homogeneous solution of different gases: Nitrogen, oxygen, water vapor, carbon dioxide….etc.

Solid Solution Metals are often mixed together to form a solid solution called an ALLOY Brass is a solid solution of zinc and copper

Liquid Solution Most of the solutions in Chemistry are in the liquid phase Most common solution is a solid substance dissolved in a liquid

Liquid Solution = solvent + solute Solute is the solid (present in small amounts) Solvent is the liquid (present in large amounts) When the 2 are mixed, the final result is a solution

Liquid Solution = solvent + solute

Solvents The most common solvent is water. It is often called the Universal Solvent. Many (but not all!) substances will dissolve in water Can you think of a substance that does NOT dissolve in water?

Aqueous Solutions A solution made with water as the solvent is called an aqueous solution (aq) NaCl (s) Na+ (aq) + Cl- (aq) A salt water solution

Solvents There are solvents other than water. These are often used to dissolve substances that do not dissolve in water. Can you think of a type of solvent besides water?

What do liquid solutions look like? homogeneous mixtures Clear, not cloudy May have color The solute does not settle to the bottom Pass through filters

Are these solutions?

Are these solutions?

Solubility Substances that dissolve easily are called SOLUBLE Salt is soluble in water

Solubility Substances that do not dissolve easily are called insoluble Nickel is insoluble in water

Factors that influence solubility Why are some substances soluble in water, but not in other liquids? Why are some substances not soluble in water? What can be done to make a substance dissolve more easily? It helps to understand what controls solubility….

Factors that influence solubility #1 TEMPERATURE As temperature increases, most solids become more soluble in water. Ex. Sugar in ice tea vs. hot tea

Factors that influence solubility #1 TEMPERATURE As temperature increases, most gases become less soluble in water. Ex. The carbon dioxide (fizz) in cold soda vs. hot soda

Factors that influence solubility #2 Pressure As pressure increases, most gases become more soluble in water. Ex. The carbon dioxide (fizz) in soda in a pressurized can vs. soda that has been left open (goes “flat” at low pressure)

Factors that influence solubility #2 Pressure PRESSURE HAS NO EFFECT ON LIQUID OR SOLID SOLUTES!!!

Factors that influence solubility #3 The Nature of the solute and solvent where “like” refers to the polarity of the molecule Like dissolves Like

Factors that influence solubility #3 The Nature of the solute and solvent POLAR solvents dissolve POLAR solutes (Polar includes ionic compounds) “Like dissolves Like”

Factors that influence solubility #3 The Nature of the solute and solvent POLAR solvents dissolve POLAR solutes So ionic NaCl will dissolve in polar water Like dissolves Like”

What is going on at the molecular level when a polar substance dissolves? Cl- The polar water molecule pulls apart the ionic compound into anions and cations If you evaporate away the water, the Na and Cl will join together again to make NaCl (s)

attraction between the positive end of the water Na+ Cl- For this to happen, the attraction between the positive end of the water molecule and the negative ion must be STRONGER than the attraction between the positive and negative ion.

Factors that influence solubility #3 The Nature of the solute and solvent NON POLAR solvents dissolve NON POLAR solutes Non polar solvents and solutes simply mix together “Like dissolves Like”

Factors that influence solubility #3 The Nature of the solute and solvent fats and oil are non polar Oil (non polar) will not dissolve in water (polar) “Like dissolves Like”

Soaps Soaps are long molecules that have a polar end and a non polar end Grease (non polar) does not dissolve in water alone (polar), but if soap is added, the grease will dissolve in the non polar end of the soap. The polar end of the soap allows it to dissolve in the water, washing away the grease