Chapter 6 Solutions and Colloids

2 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount SolutionSolventSolute Soft drink (l) Air (g) Soft Solder (s) H2OH2O N2N2 Pb Sugar, CO 2 O 2, Ar, CH 4 Sn aqueous solutions of KMnO 4

Solutions Solvents are typically liquids, but can also be gases and (less commonly) solids. Solutes are typically solids, gases, and other liquids. Table 6.1 page 179

Distinguishing Characteristics Homogenous Mixture Will not separate with time Cannot separate by filtration Can have different concentrations Transparent Separated into pure components

Solubility Solubility is a description of the amount of solute that is dissolved in a certain amount of solvent. When two liquids are soluble, they are miscible Solubility depends on: – Type of solute – Type of solvent – Solute-solvent interactions – Temperature, – The presence of other solutes or contaminants.

6 “like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l)

Solubility and Solutions Solutions have varying degrees of saturation: – Unsaturated solution – Saturated solution – Supersaturated solution

Unsaturated Solutions Unsaturated solution – Has less than the maximum amount of solute in solvent. – More solute can be dissolved in an unsaturated solution.

Saturated Solutions Saturated solution; – Has the maximum amount of solute in solvent. – No more solute can be dissolved in a saturated solution

Supersaturated solution Supersaturated solution: – Has more than the maximum amount of solute in solvent. – It is highly unstable and solute usually settles out of the solution in order to lower its saturation.

Solubility and Temperature Solubility depends on temperature. For solid solutes, the solubility increases as temperature increases. More sugar will dissolve in a hot drink than in a cold drink. For gas solutes, the solubility decreases as temperature increases. This is why carbonated beverages will fizz more if the drink is warm. This also explains the environmental impact of global warming and thermal pollution to bodies of water.

Gas Solutes Solubility of a gas solute also depends on the vapor pressure of the gas above the liquid. Henry’s Law – Higher pressures lead to higher solubility – Lower pressures lead to lower solubility. This explains why carbonated beverages lose their carbonation after they are opened. – When the bottle is opened, the gas above the liquid is now at atmospheric pressure, a lower pressure.

Concentration Concentration is the specific amount of solute dissolved in a solution. We will learn four ways to express the concentration of a solution

14 Preparing a Solution of Known Concentration

Mass Percent Mass percent (percent mass or percent weight) (% m/m or % w/w) is the mass of a solute per total mass of solution. – mass of solution = mass of solute + mass of solvent.

Volume Percent Volume percent (% v/v) is the volume of solute per total volume of solution. (Give equation.)

Mass-Volume Percent Mass-volume percent (percent weight by volume or percent mass by volume) (% m/v or %w/v) is the mass of a solute per total volume of solution. Problem 6.1 page 185 Problem 6.2 page 186

Molarity Molarity (M) is the number of moles of solute per liters of solution. M = mol/V

Conversion Factor Molarity can be used as a conversion factor, just like the percent concentrations. Write the conversion factors from: – 1.85 M HCl – 0.72 M KBr Problem 6.3 page 187 Problem 6.4 page 187 Problem 6.5 page 188 Problem 6.6 page 188

20 Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. Dilution Add Solvent Moles of solute before dilution (i) Moles of solute after dilution (f) = MiViMiVi MfVfMfVf =

Dilution Dilution is the process of decreasing the concentration of a solution by adding more solvent. The equation for dilution calculations is: C 1 V 1 = C 2 V 2 – where C can be any concentration (molarity) as well as percent concentrations. Problem 6.7 and 6.8 page 189

Parts per Million Exactly like % (parts per 100) Write out 1 ppm Write out 1 ppb (parts per billion) Problem 6.9 page 191

23 Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.   H2OH2O Solvated is a term used for all solvents

Hydrates Water molecules in a crystalline solid Anhydrous: The crystal withou water – CaSO 4 ∙ H 2 O Hygroscopic: Crystals that become hydrated from the air

25 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount SolutionSolventSolute Soft drink (l) Air (g) Soft Solder (s) H2OH2O N2N2 Pb Sugar, CO 2 O 2, Ar, CH 4 Sn aqueous solutions of KMnO 4

26 Nonelectrolyte does not conduct electricity? No cations (+) and anions (-) in solution C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) H2OH2O

27 Water will dissolve covalent compountds Notice the solutions become ionic. Why is that important for our bodies?

28 Hydronium ion, hydrated proton, H 3 O +

29 A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance. Colloid versus solution collodial particles are much larger than solute molecules collodial suspension is not as homogeneous as a solution colloids exhibit the Tyndall effect

30

31 Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Boiling-Point Elevation  T b = K b m Freezing-Point Depression  T f = K f m Osmotic Pressure (  )  = MRT

32 Colligative Properties of Electrolyte Solutions 0.1 m NaCl solution 0.1 m Na + ions & 0.1 m Cl - ions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 m NaCl solution0.2 m ions in solution van’t Hoff factor (i) = actual number of particles in soln after dissociation number of formula units initially dissolved in soln nonelectrolytes NaCl CaCl 2 i should be 1 2 3

33 Boiling-Point Elevation  T b = i K b m Freezing-Point Depression  T f = i K f m Osmotic Pressure (  )  = iMRT Colligative Properties of Electrolyte Solutions