Solutions Chapters 7.1 and 7.2

7.1 Types of Solutions Solution a homogeneous mixture of a solvent and one or more solutes. it is uniform throughout. Solvent - a substance that has other substances dissolved in it. Ex. In saltwater - water is the solvent. In Kool-Aid - water is the solvent. Solute - a substance that is dissolved in a solution. Ex. In saltwater - salt is the solute. In Kool-Aid - the Kool-Aid and the sugar is the solute.

Solutions have variable composition - different ratios of solute to solvent. Dilute solution - low solute to solvent ratio Concentrated solution - high solute to solvent ratio   When a solute dissolves in a solvent - no chemical reaction occurs. Therefore, the solute and the solvent can be separated using physical properties: boiling points, melting points, distillation, filtration, dissolution , and chromatography, etc.

Types of Solutions Solid - gas, liquid or solid solute dissolved in a solid solvent.   ** Alloy - solid solutions of metals. Liquid - gas, liquid, or solid dissolved in a liquid solvent. Aqueous - a solution where water is the solvent. Gas - gas, liquid or solid dissolved in a gaseous solvent. Special Solution Descriptions Miscible - liquids that readily dissolve in one another. Ex. - Ethanol and water. Immiscible - liquids that do not readily dissolve in one another. Ex. Oil and water

Table 7.1 page 238

7.2 Factors That Affect The Rate of Dissolving Rate of dissolving - how quickly a solute dissolves in a solvent.  Three Factors Affect the Rate of Dissolving 1. Temperature For most solids, the rate of dissolving is greater as temperature increases. 2. Agitation Stirring or shaking increases the rate of dissolving. 3. Particle size Decreasing the particle size increases the rate of dissolving.

How Compounds Dissolve The reasons why a solute may or may not dissolve in a solvent depends on the forces of attraction involved between the two substances: - forces of attraction between the solute-solute particles - forces of attraction between the solvent-solvent particles - forces of attraction between the solute-solvent particles When the forces of attraction between the solute and the solvent is the strongest force of attraction, a solution will form. The strength of each attraction affects solubility.

Dissolving At the Molecular Level 1. Weaken/Break the FOA between the solute particles 2. Weaken/Break the FOA between the solvent particles 3. The attraction between the solute and the solvent particles replaces the original FOA.

Dissolving Ionic Compounds In Water Weaken/Break the FOA between the solute-solute particles. - ionic compound - need to weaken/break the ionic bonds. 2. Weaken/Break the FOA between the solvent-solvent particles. - water is a covalent compound - need to weaken/break the intermolecular forces - LD, DD, HB 3. A FOA forms between the solute-solvent particles. This FOA is Ion-Dipole Forces. - if it is stronger than the other FOA in the solution then the solute will dissolve. - if it is NOT stronger than the other FOA in the solution then the solute will NOT dissolve. (Remember the solubility chart)

Ion-Dipole Forces of Attraction These forces of attraction will occur when an ionic compound dissolves in a polar substance (water). When these forces are strong, they can pull the ions apart from each other and into solution. Ion-dipole forces - the force of attraction between an ion and a polar molecule. Ex. When NaCl dissolves in water, there is an attraction between the partially negative charges of the oxygen in the water molecule and the positive Na+ ion. At the same time, the partially positive charge of hydrogen attracts the Cl- ions. This pulls the ions into solution. This would increase the boiling point of the solution.

Animation of salt dissolving...

Electrolyte - when ions are present in aqueous solution Electrolyte - when ions are present in aqueous solution. - solutions with electrolytes will conduct electricity. Equation: NaCl (s) → Na+ (aq) + Cl- (aq) Non-Electrolyte - when a substance dissolves but will not conduct electricity. Equation: C12H22O11 (s) → C12H22O11 (aq)

Dissolving Covalent Compounds Polar Compounds 1. Polar covalent compound - need to weaken/break the IMF - LD, DD 2. water - need to weaken/break the IMF - LD, DD, HB - more dipole-dipole forces replace the original forces. Non-Polar Compounds 1. Non-polar compound - need to weaken/break the IMF - LD 2. Water - need to weaken/break the IMF - LD, DD, HB 3. LD not strong enough to weaken/break water’s IMF - will not dissolve.

Sucrose – a covalent compound that will dissolve due to numerous possibilities of hydrogen bonding with water molecules.

General Trend  LIKE dissolves LIKE !!!!  Non-polar will dissolve non-polar.  Polar will dissolve polar.

Dissociation Equations When ionic compounds dissolve in water, they dissociate into positive and negative ions that are surrounded by water molecules. Dissociation Equation – a balanced chemical equation that shows all ions that are produced when an ionic compound dissolves in water. Equations must be balanced, include charges for the ions and state subscripts. Use the solubility chart to decide if a substance will dissolve. If it is soluble – dissociate it. If it is not soluble – it stays together.

Solubility Chart

Dissociation the following substances: a) AlCl3 b) KOH c) AgCl d) Sr(ClO3)2 AlCl3 (s) → Al3+(aq) + 3 Cl-(aq) KOH (s) → K+(aq) + OH-(aq) AgCl (s) → AgCl(s) Sr(ClO3)2(s) → Sr2+(aq) + 2 ClO3-(aq)

Reactions That Occur in Solution When reactions occur in solution – it is often desirable to write the equation in ionic form. As long as water, a gas, or a precipitate forms, there is a reaction. (There must be a state change for some ions.) Ex. A soln of barium chloride reacts with a soln of sodium sulfate. Equation: BaCl2(aq) + Na2SO4(aq) → 2NaCl + BaSO4 BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s)

BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s) Ionic Equation: BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s) Net Ionic Equation: Remove Spectator Ions Ba2+(aq)+ 2Cl-(aq) + 2Na+(aq) + SO42-(aq)→ 2Na+ (aq) + 2Cl-(aq) + BaSO4 (s)  Ba2+(aq) + SO42-(aq)→ BaSO4 (s) Ba2+(aq) + 2Cl-(aq) + 2Na+(aq) + SO42-(aq) → 2Na+ (aq) + 2Cl-(aq) + BaSO4 (s)

1. Write dissociation equations for the following: Work Sheet 1. Write dissociation equations for the following: sodium acetate Mercury (I) acetate silver chlorate potassium hydroxide lead (II) phosphate 2. Write balanced net ionic equations for the following reactions: NaBr (aq) + Pb(NO3)2 (aq) → Al(NO3)3 (aq) + Na2S (aq) → (NH4)3PO4 (aq) + Cu(NO3)2 (aq) → AgNO3 (aq) + KI (aq) → KOH (aq) + Ba(ClO4)2 (aq) →

Solubility Solubility - the mass of solute that dissolves in a given quantity of solvent at a specific temperature. Ex. Solubility of Salt - 36 g of NaCl in 100 mL at 20 oC. ¸ or 36 g at 20 oC. 100cm3 Molar Solubility - amount in moles, volume in litres at a certain temperature.

soluble - a solute that has a greater solubility than 1 g/100mL. Solubility Terms:  soluble - a solute that has a greater solubility than 1 g/100mL.  insoluble - a solute that has a lower solubility than 1g/100 mL.  sparingly soluble - solutes with solubilities between these limits  saturated solution - a solution in which when no more of a particular solute will dissolve at a particular temperature. unsaturated solution - a solution in which more of a particular solute can be dissolved at a specific temperature.

Solubility Curves Solubility curves show the solubility of a substance at various temperatures. The curve shows the # of grams of solute in a saturated solution containing 100 mL or 100 g of water at a certain temperature. Any amount of solute below the line indicates the solution is unsaturated at a certain temperature.