Solutions

Ch.13

(13-1) Mixtures

• Suspension: appears uniform, but separates out when settled– Ex: muddy water

• Colloid: small particles suspended in a solvent & doesn’t settle out– Ex: milk

Solution

• Solvent: substance in which solute dissolves

• Solute: substance dissolved

• Aqueous: soln in which solvent is H2O

Concentration

• Amt. of solute in a specific amt. of solvent or soln– Low conc. = dilute soln– High conc. = concentrated soln

Measuring Conc.

• Molarity (M) = mols of solute

L of soln

• Molality (m) = mols of solute

kg solvent

Molarity Practice

What’s the molarity of a KCl soln that has a V of 400 mL & contains 85 g of KCl?

1. List knownV = 400 mL

m = 85 g

Molarity Practice

2. Convert into appropriate units400 mL x 1 L = 0.4 L

1000 mL

85 g KCl x 1 mol = 1.14 mol KCl

74.6 g

3. Substitute & solveM = mols = 1.14 mol = 2.85 M

L 0.4 L

Molality Practice

How many mols of NaF are required to make a 0.30 m soln using 0.6 kg of water?

1. List knownm = 0.30

kg solvent = 0.6

Molality Practice

2. Write eq., substitute, & solve

m = mols mols = (m)(kg)

kg = (0.30 m)(0.6 kg)

= 0.18 mol

Separating Mixtures

• Filtration

• Evaporation

• Centrifuge

• Distillation– Drinking water from sea water

• Chromatography– Separating dyes in ink

(13-2) Solubility

• Max amt. of a chemical that will dissolve in a given quantity of solvent at a specified T

• Soluble: can be dissolved

• Insoluble: does not dissolve

Rxn of KI soln & Pb(NO3)2 soln

Shellfish form their shells from CaCO3. The organism secretes Ca2+ from cells in contact w/ seawater, which contains dissolved CO2, some of which is present as CO3

2-. The ions combine to give a precipitate of CaCO3.

Kidney stones are generally also insoluble calcium cmpds such as calcium carbonate, calcium phosphate, or calcium oxalate.

Henry’s Law

• Solubility of a gas in a liquid is directly proportional to the partial P of that gas– Pop bottle w/ CO2

• Gas solubility depends on P & T– Inc. P, inc. solubility– Inc. T, dec. solubility

Saturated

• Containing amt. of solute specified by solubility

• Supersaturated: containing more than the amt. of solute specified by solubility

Miscible

• Liquids that dissolve in 1 another– Similar polarity

• Immiscible: liquids that will not dissolve in each other– Ex: oil & water

(13-3) Conductivity

• Ability to conduct electric current

• Electrolyte: conducts electricity– Ex: NaCl dissolved in H2O

– Ionic

• Nonelectrolyte: does not conduct– Ex: C6H12O6 dissolved in H2O

– Covalent

Electrolytes

• Strong electrolyte: almost completely dissociates (separates into fragments) in soln– Ex: NaCl(s) + H2O(l) Na+(aq) + Cl-(aq)

• Weak electrolyte: small % dissociates in soln– Ex: NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq)

Hydronium Ion

• H ion bonded to a H2O molecule (H3O+)

• Hydration: H2O molecules surround each ion in a soln

(13-4) Colligative Properties

• Physical properties that are dependent on the # of solute particles present rather than the particle identity

Boiling-point Elevation

• Difference b/w the bp of a soln & a pure substance

• Freezing-point depression: difference b/w the fp of a pure solvent w/ a soln