SOLUTIONS Chapter 12

Solutions Homogeneous mixtures of two or more substances in a single phase  Example: salt water  The salt is interspersed among the water. The mixture appears uniform throughout.

Types of Mixtures Let’s talk about what happens when sugar and water are mixed together. Which one is soluble also called the solute? (Which one is capable of dissolving?) Which one is the solvent? (The one that does the dissolving) All solutions have solutes and solvents. Let’s look at Table 1 on page 402

Types of Solutions Homogeneous Solutions  Same throughout (salt water, sugar in water, kool aid Suspensions  Solvent is too large to completely dissolve unless being constantly stirred.  Ex: Italian Dressing, muddy water, some medicines Colloids  Particles are larger than solutions but smaller than suspensions  Ex: paints, gelatin, milk, mayonnaise, shaving cream, smoke, fog, mist, clouds, cheese, butter

Tyndall Effect Many colloids appear homogeneous because the individual particles cannot be seen. The particles, however, are large enough to scatter light. Colloids show the Tyndall effect and particles do not settle.

Tyndall Effect

Electrolytes Vs. Nonelectrolytes Electrolytes- a substance that dissolves in water and conducts electricity  Example: Salts, Gatorade  In the 8 th grade we used copper (II) sulfate to make a battery and it lit the light bulb. We dissolved it in water, hooked it to the battery, and connected it to the light bulb. It was able to carry the electric current to the light bulb.

Section 2: The Solution Process Factors Affecting the Rate of Dissolution  Increasing the surface area of the solute  Agitating a Solution  Heating a Solution

Solubility If you add spoonful after spoonful of sugar to tea, eventually no more sugar will dissolve. For every combination of solvent with a solid solute at a given temperature, there is a limit to the amount of solution that can be dissolved. Solution equilibrium- the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates.

Saturated VS. Unsaturated Saturated Solution: a solution that contains the maximum amount of dissolved solute  How can you tell?  If you add any more of that solution, it falls to the bottom Unsaturated: a solution that contains less solute than a saturated solution

Supersaturated Solutions A solution that contains more dissolved solute than a saturated solution contains under the same conditions. A supersaturated solution may remain unchanged for a long time if it is not disturbed, but once crystals begin to form, the process continues until equilibrium is reestablished at the lower temperature.  Why do you care? This is how rock candy is made.

Solutions

Solubility Values The solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature. Look at table 4 on page 410

Solute-Solvent Interactions “Like dissolves like” Polar likes polar Nonpolar likes nonpolar

Liquid Solutes and Solvents Immiscible- liquids that are not soluble Miscible- Liquids that dissolve Water and Alcohol Demo

Effects of Pressure on Solubility Changes in pressure have very little effect on the solubilities of liquids or solids in liquid solvents However, increases in pressure increase gas solubilities in liquids. Henry’s Law: The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid  Applies to gas-liquid solutions at constant temperature

Henry’s Law Continued Effervescence- the rapid escape of a gas from a liquid in which it is dissolved Examples: Coke-A-Cola  When you have a bottled coke, the CO 2 is under high pressure above the solvent. If you press on the bottle before opening, the bottle feels firm. This is due to the pressure of the gas. When you open the bottle it fizzes. The gas particles escape from the liquid and you see the bubbles.

Effects of Temperature on Solubility Increasing the temperature of GASES usually decreases solubility. Explain to why hot cokes tend to “fizz” more than cold cokes. The effect of temperature on the solubility of solids in liquids is more difficult to predict. Often, temp increases the solubility of solids.

Solubility Charts

To what temperature will 400 g of water need to be heated to dissolve 160 of NaCl?

How many grams of sodium nitrate will dissolve in 300 g of water at 40C?

How many grams of water need to be added to dissolve 150 g of sodium nitrate at 60C?

How many grams of potassium nitrate precipitates when a saturated solution of potassium nitrate at 70C is cooled to 20C?

Enthalpies of Solution The amount of energy absorbed as heat by the solution when a specific amount of solute dissolves in a solvent. Heat energy is represented by an H  Endothermic: Energy is absorbed  Exothermic: Energy is released (-∆H)

Section 3: Concentrations The measure of the amount of solute in a given amount of solvent or solution  %  PPM  Molarity  Molality

% as Concentration Ex: 70% salt water 70 grams of salt for every 100 grams of water Remember % is based on 100

Molarity (M) Moles of solvent per Liter of solution You have 3.5 L of solution that contains 90.0 grams of sodium chloride. What is the molarity of that solution? You have 0.8 L of a 0.5M solution. How many moles of HCl does this solution contain?

Molarity (M) To produce 40.0 grams of silver chromate, you will need at least 23.4 grams of potassium chromate in solution as a reactant. All you have on hand is 5 L of a 6.0 M K 2 CrO 4 solution. What volume of the solution is needed to give you the 23.4 g K2CrO4 needed for the reaction?

Molality (m) Moles of solute per kg of solvent A solution was prepared by dissolving 17.1 g of sucrose (table sugar C 12 H 22 O 11 ) in 125 g of water. Fine the molal concentration of this solution. A solution of iodine in carbon tetrachloride is used when iodine is needed for certain chemical tests. How much iodine must be added to prepare a m solution of iodine in CCl 4 if 100 g of CCl 4 is used?