SOLUTIONS What is a solution? What does that mean? Possible to have any state dissolved in any other; however, most inorganic rxns which involve solutions have solid or gas dissolved in water, so our emphasis will be on aqueous solutions. Solution Composition [concentration] Mass % - mass solute x 100 mass solution Mole fraction of A = n A = χ A n A + n B Molality = mol solute kg solvent Molarity = L solution Normality = # equivalents L solution For acid-base, 1 eq = mass of A or B which produces 1 mol of H + or OH -. For redox 1 eq = quantity of oxid or red agent which will provide or accept 1 mol of e -.

SOLUTIONS What is the molality of a solution prepared by dissolving 18.3 g of cobalt(II) nitrate in 500. mL H 2 O? What is m for the ions? How would you prepare 250. mL of a 2.00 M solution of NaOH? What is the normality of a M solution of HCl? H 2 SO 4 ? Dilution Dilution is adding solvent to decrease the concentration of a solution Dilution is adding solvent to decrease the concentration of a solution The amount of solute stays the same, but the concentration decreases The amount of solute stays the same, but the concentration decreases Dilution Formula: M s x V s = M d x V d Dilution Formula: M s x V s = M d x V d Describe how to prepare 100. mL of a 0.25M solution from a 2.00M stock solution Describe how to prepare 100. mL of a 0.25M solution from a 2.00M stock solution

Determining Concentration of an Unknown Solution The amount of light absorbed is related to Beer’s Law (A = εbc) and can be compared to a calibration curve to determine the concentration of the colored substance in the sample. The Beer-Lambert Law One way to determine an unknown concentration, is to measure the amount of light absorbed by a colored solution. A sample is placed in a spectrophotometer adjusted to absorb a specific λ of light. The amount of light transmitted or absorbed by the solution is measured (see lab handout Analysis of Food Dyes…)

Example: A 50.0 mL sample containing Cr 3+ ions is diluted to 250. mL and shows an absorbance of at 415 nm. Determine the concentation of chromium(III) ions in the original 50 mL sample. Example: A 50.0 mL sample containing Cr 3+ ions is diluted to 250. mL and shows an absorbance of at 415 nm. Determine the concentation of chromium(III) ions in the original 50 mL sample. 0.17M x mL/50.0 mL = 0.85M Note: If the original solution has been diluted multiply by the ratio (volume dil/vol. orig.). If reduced (evap) multiply by the ratio (reduced vol./orig vol.).

Titration Titration is the use of a standard solution to determine the concentration of another (unknown) solution. A certain volume of one solution (standard) which is acidic or basic, is added to a known volume of a solution whose concentration is unknown (also acid or base, opposite of the standard solution). The volume of standard added is just enough to neutralize the unknown. This is determined by using an indicator. The concentration of the unknown solution can then be calculated using the equation M u V u = M s V s Example:25.0 mL of 0.250M NaOH is titrated with 15.00mL of an acetic acid solution. M u = MsVsMsVs ____ VuVu = (0.250 M)(25.0 mL)_______________ 15.0 mL = M

Calculate the volume of M of sulfuric acid needed to completely neutralize 10.0g of sodium bicarbonate.

Solubility Rule of thumb?Why? Explained by energies of solution formation. 3 parts to solution formation: Breaking up (expanding) the solute ∆H 1 positive and higher for polar/ionic Overcoming the intermolecular forces in (expanding) the solvent ∆H 2 Also + and higher for polar/ionic Solvent and solute interaction to form solution ∆H 3 negative Enthalpy (heat) of solution∆H soln =Heat of SolvationLattice Enthalpy∆H 1 + ∆H 2 +∆H 3 Illustrations Oil in water; NaCl in water;I 2 in hexane Identify which in each pair would be most soluble in water: hexane or ethanolEthanol or octanol ↑ temperature generally increases solubility for solid in liquid ↑ pressure increases solubility of gas in liquid

Colligative Properties Adding a solute to a solvent affects the properties of the solvent. Vapor pressure is depressed Raoult’s Law: PA = P0A x (nA/nsoln) Distillation Boiling Point is elevated Freezing point is depressed Osmotic Pressure is elevated Osmosis "distillation." Online. Britannica Student Encyclopædia. 27 Sept Place these in order of increasing bp (all are 1.00m aq solutions): glucose, calcium chloride, hydrochloric acid, nitrous acid.