Solutions Chapter 14 Dr. Schuerch

Properties of Solutions Solution Formation –Solutions are homogeneous mixtures that may be solid, liquid, or gas The compositions of the solvent and the solute determine whether a substance will dissolve. Aqueous solutions are solutions with water as the solvent. Stirring (agitation), temperature, and the surface area of the dissolving particles determine how fast the substance will dissolve –The three factors work by increasing contact of the solute with the solvent

Properties of Solutions Solubility –Solubility is the amount of solute that dissolves in a given quantity of solvent at a specified temperature and pressure to produce a saturated solution – A saturated solution contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure (no more solute will dissolve when reached) –A unsaturated solution contains less solute than the same saturated solution Unsaturated solutions can be concentrated or dilute Miscibility –When two liquids can dissolve into each other they are considered to be miscible Example – Alcohol and Water –When two liquids can not dissolve into each other they are immiscible Example – Oil and Water

Factors Affecting Solubility Temperature –Affects solubility of solids, liquids, and gases Increases the solubility of most solids Can result in supersaturated solutions when solution cools »A supersaturated solution contains more solute than it can theoretically hold at a given temperature Decreases the solubility of most gases Pressure –Strongly affects the solubility of gases. Henry’s law – at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) S2S2 P2P2 S1S1 P1P1 =

Solution Composition: Mass Percent Mass Percent is defined as mass of solute divided by the mass of solution x 100% –Mass is usually in grams 5g NaCl 45g H 2 O10% NaCl +=

Solution Composition Molarity (M) Molarity is the number of moles of solute divided the volume of the solution in liters Water Level (0.5 L) 58.5g NaCl (1 mol NaCl) 1 Liter Mark 1 Liter Volumetric Flask 1.Dissolve solute into partially filled volumetric flask2.Add water to 1 L mark Above is an example of how to make a standard solution, a solution whose concentration is accurately known.

Solution Composition: Calculating Molarity Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50 L of solution

Solution Composition: Calculating Molarity Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8 mL of solution

Solution Composition: Calculating Ion Concentration from Molarity Give the concentrations of all the ions in each of the following solutions M Co(NO 3 ) M FeCl 3

Solution Composition: Calculating Number of Moles from Molarity How many moles of Ag + ions are present in 25 mL of a 0.75 M AgNO 3 solution?

Solution Composition: Calculating Mass from Molarity To analyze the alcohol content of a certain wine, a chemist needs 1.00 L of an aqueous M K 2 Cr 2 O 7 (potassium dichromate) solution. How much solid K 2 Cr 2 O 7 (molar mass = g) must be weighed out to make this solutions?

Dilution To save time and space in laboratory, solutions that are routinely used are often purchased or prepared in a concentration form called a stock solution Water or another solvent is then added to dilute the stock solution to achieve the desired concentration Dilution – adding more solvent to a solution Molarity 1 x Volume 1 = Molarity 2 x Volume 2

Calculating Concentrations of Diluted Solutions What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H 2 SO 4 solution?

Serial Dilutions

Stoichiometry of Solution Reactions Steps for solving stoichiometric problems involving solutions 1.Write the balanced equation for the reaction. For reactions involving ions, it is best to write the net ionic equation 2.Calculate the moles of reactants 3.Determine which reactant is limiting 4.Calculate the moles of other reactants of products, as required 5.Convert to grams or other units, if required

Solution Stoichiometry: Calculating Mass of Reactants and Products Calculate the mass of solid NaCl that must be added to 1.50 L of a M AgNO 3 solution to precipitate all of the Ag + ions in the form of AgCl. Calculate the mass of AgCl formed.

Solution Stoichiometry: Determining Limiting Reactants and Calculating Mass of Products When Ba(NO 3 ) 2 and K 2 CrO 4 react in aqueous solution, the yellow solid is BaCrO 4 is formed. Calculate the mass of BaCrO 4 that forms when 3.50x10 -3 mol of Solid Ba(NO 3 ) 2 is dissolved in 265 mL of M K 2 CrO 4 solution.

Neutralization Reactions Neutralization reactions are those that occur between an acid and base forming water as one of the products –When just enough base as been added to react exactly with strong acid in a solution or vice versa, we say the solution has been neutralized What do you think the pH of the solution is when it has been neutralized?

Solution Stoichiometry: Calculating Volume in Neutralization Reactions What Volume of a M HCl Solution is needed to neutralize 25.0 mL of a M NaOH solution?

Solution Composition: Normality One equivalent of an acid is the amount of that acid that furnish 1 mole of H+ ions One equivalent of a base is the amount of that base that can furnish 1 mole OH- ions –The equivalent weight of an acid or base is the mass in grams of 1 equivalent (equiv) of that acid or base FormulaMolar Mass H+ or OH- Produced per molecule Equivalent Weight in (g) HCl H 2 SO H 3 PO NaOH 40.01

Solution Composition: Normality Normality (N) is defined as the number of equivalents of solute per liter of solution Notice that normality times volume equals equivalents

Solution Stoichiometry: Calculating Normality A solution of sulfuric acid contains 86 g of H 2 SO 4 per liter of solution. Calculate the normality of this solution.

Solution Stoichiometry: Calculating Normality Calculate the normality of a solution containing 23.6 g of KOH in 755 mL of solution

Solution Stoichiometry: Using Normality in Calculations What volume of a N KOH solution is required to react exactly with L of 0.45 N H 3 PO 4?