SOLUTIONS AND SOLUBILITY DEFINITIONS A solution is a

SOLUTIONS AND SOLUBILITY

DEFINITIONS A solution is a homogeneous mixture A solute is dissolved in a solvent. § solute is the substance being dissolved § solvent is the liquid in which the solute is dissolved § an aqueous solution has water as solvent A saturated solution is one where the concentration is at a maximum - no more solute is able to dissolve. § A saturated solution represents an equilibrium: the rate of dissolving is equal to the rate of crystallization. The salt continues to dissolve, but crystallizes at the same rate so that there “appears” to be nothing happening.

Substances that make up the solution can be: Solid- salt dissolved in water Liquid- HCl dissolved in water Gas- Carbon Dioxide dissolved in water- pop Not every liquid dissolves every solid ex. Na. Cl dissolves in water but not gasoline, parrafin wax dissolves in gasoline but not water. Liquids are similar- liquids that dissolve other liquids are miscible- ethanol dissolves in water. - liquids that do not dissolve each other are immiscible- oil and water.

A common phrase that is used to determine which substances dissolve which is “like dissolves like”. Meaning polar substances dissolve polar substances and nonpolar dissolve non polar. Examples of solutions not in liquid phase: Air- made of N 2, O 2 CO 2 and others Metal Alloys- brass- made up of zinc and copper

REACTIONS INVOLVING PRECIPITATES When two liquids (with dissolved substances) mix and a solid forms it is called a precipitate.

REMEMBER- NET IONIC EQUATIONS When a solution of Pb(NO 3)2 is mixed with a solution of KI the result is a precipitate of Pb. I and a solution of KNO 3. Pb(NO 3)2(aq) + 2 KI(aq) Pb. I 2(s) + 2 KNO 3(aq) Remember- dissociation equations Net Ionic Equation

% CONCENTRATION % (w/w) = % (w/v) = % (v/v) =

1. How many m. L of a 14 M stock solution must be used to make 250 m. L of a 1. 75 M solution? 2. You have 200 m. L of 6. 0 M HF. What concentration results if this is diluted to a total volume of 1 L? 3. 100 m. L of 6. 0 M Cu. SO 4 must be diluted to what final volume so that the resulting solution is 1. 5 M? 4. What concentration results from mixing 400 m. L of 2. 0 M HCl with 600 m. L of 3. 0 M HCl? 5. What is the concentration of Na. Cl when 3 L of 0. 5 M Na. Cl are mixed with 2 L of 0. 2 M Na. Cl? 6. What is the concentration of Na. Cl when 3 L of 0. 5 M Na. Cl are mixed with 2 L of water? 7. Water is added to 4 L of 6 M antifreeze until it is 1. 5 M. What is the total volume of the new solution? 8. There are 3 L of 0. 2 M HF. 1. 7 L of this is poured out, what is the concentration of the remaining HF?

DILUTION PROBLEMS (1 -6, 6 TWO WAYS) 1. M 1 = 14 M, V 1 = ? , M 2 = 1. 75 M, V 2 = 250 m. L V 1 = M 2 V 2 / M 1 = (1. 75 M)(0. 250 L) / (14 M) 2. V 1 = 0. 03125 L = 31. 25 m. L M 1 = 6 M, V 1 = 0. 2 L, M 2 = ? , V 2 = 1 L M 2 = M 1 V 1 / V 2 = (6 M)(0. 2 L) / (1 L) 3. M 2 = 1. 2 M M 1 = 6 M, V 1 = 100 m. L, M 2 = 1. 5 M, V 2 = ? V 2 = M 1 V 1 / M 2 = (6 M)(0. 100 L) / (1. 5 M) V 2 = 0. 4 L or 400 m. L

DILUTION PROBLEMS (4 - 6) 4. # mol = (2. 0 mol/L)(0. 4 L) + (3. 0 mol/L)(0. 6 L) = 0. 8 mol + 1. 8 mol = 2. 6 mol # L = 0. 4 L + 0. 6 L # mol/L = 2. 6 mol / 1 L = 2. 6 mol/L 5. # mol = (0. 5 mol/L)(3 L) + (0. 2 mol/L)(2 L) = 1. 5 mol + 0. 4 mol = 1. 9 mol # mol/L = 1. 9 mol / 5 L = 0. 38 mol/L 6. # mol = (0. 5 mol/L)(3 L) + (0 mol/L)(2 L) = 1. 5 mol + 0 mol = 1. 5 mol # mol/L = 1. 5 mol / 5 L = 0. 3 mol/L Or, using M 1 V 1 = M 2 V 2, M 1 = 0. 5 M, V 1 = 3 L, M 2 = ? , V 2 = 5 L

DILUTION PROBLEMS (7, 8) 7. M 1 = 6 M, V 1 = 4 L, M 2 = 1. 5 M, V 2 = ? V 2 = M 1 V 1 / M 2 = (6 M)(4 L) / (1. 5 M) V 2 = 16 L 8. The concentration remains 0. 2 M, both volume and moles are removed when the solution is poured out. Remember M is mol/L. Just like the density of a copper penny does not change if it is cut in half, the concentration of a solution does not change if it is cut in half.

% CONCENTRATION: % MASS EXAMPLE 3. 5 g of Co. Cl 2 is dissolved in 100 m. L solution. Assuming the density of the solution is 1. 0 g/m. L, what is concentration of the solution in % mass? %m = 3. 5 g Co. Cl 2 100 g H 2 O = 3. 5% (m/m)

CONCENTRATION: MOLARITY EXAMPLE If 0. 435 g of KMn. O 4 is dissolved in enough water to give 250. m. L of solution, what is the molarity of KMn. O 4? As is almost always the case, the first step is to convert the mass of material to moles. 0. 435 g KMn. O 4 • 1 mol KMn. O 4 = 0. 00275 mol KMn. O 4 158. 0 g KMn. O 4 Now that the number of moles of substance is known, this can be combined with the volume of solution — which must be in liters — to give the molarity. Because 250. m. L is equivalent to 0. 250 L. Molarity KMn. O 4 = 0. 00275 mol KMn. O 4 = 0. 0110 M 0. 250 L solution

DILUTION Suppose you have 0. 500 M sucrose stock solution. How do you prepare 250 m. L of 0. 348 M sucrose solution ? When a solution is diluted, solvent is added to lower its concentration. The amount of solute remains constant before and after the dilution: moles BEFORE = moles AFTER C 1 V 1 = C 2 V 2 Concentration 0. 500 M Sucrose 250 m. L of 0. 348 M sucrose A bottle of 0. 500 M standard sucrose stock solution is in the lab. Give precise instructions to your assistant on how to use the stock solution to prepare 250. 0 m. L of a 0. 348 M sucrose solution.

FACTORS AFFECTING SOLUBILITY 1. Nature of Solute / Solvent. - Like dissolves like (IMF) 2. Temperature i) Solids/Liquids- Solubility increases with Temperature Increase K. E. increases motion and collision between solute / solvent. ii) gas - Solubility decreases with Temperature Increase K. E. result in gas escaping to atmosphere. 3. Pressure Factor i) Solids/Liquids - Very little effect Solids and Liquids are already close together, extra pressure will not increase solubility. ii) gas - Solubility increases with Pressure. Increase pressure squeezes gas solute into solvent.

SOLUBILITIES OF SOLIDS VS TEMPERATURE Solubilities of several ionic solid as a function of temperature. MOST salts have greater solubility in hot water. A few salts have negative heat of solution, (exothermic process) and they become less soluble with increasing temperature.

TEMPERATURE & THE SOLUBILITY OF GASES DECREASES AT HIGHER TEMPERATURES

SOFT DRINKS Soft drinks contain “carbonated water” – water with dissolved carbon dioxide gas. The drinks are bottled with a CO 2 pressure greater than 1 atm. When the bottle is opened, the pressure of CO 2 decreases and the solubility of CO 2 also decreases Therefore, bubbles of CO 2 escape from solution.

COLLIGATIVE PROPERTIES Dissolving solute in pure liquid will change all physical properties of liquid, Density, Vapor Pressure, Boiling Point, Freezing Point, Osmotic Pressure Colligative Properties are properties of a liquid that change when a solute is added. The magnitude of the change depends on the number of solute particles in the solution, NOT on the identity of the solute particles.