Chapter 21.2 Learning Goals Explain how solutions are formed. Define solubility and interpret solubility graphs. Describe factors that affect the concentration of solutions. Compare and contrast solubility of solid, liquid, and gaseous matter.

Solubility Curve of KNO3 Investigation 21B Solubility Curve of KNO3 Key Question: What is a solubility curve?

21.2 Water and solutions A solution is a mixture of two or more substances that is homogeneous at the molecular level. Homogeneous means the particles are evenly distributed.

21.2 Water as a mixture Muddy water is heterogeneous because it contains larger particles of soil or plant debris.

21.2 Colloids Colloids are mixtures, and look like solutions, but their particles are too small to settle to the bottom of their container over time. Examples of colloids are mayonnaise, egg whites, and gelatin.

21.2 Tyndall effect Tyndall effect is occurring if you shine a flashlight through a jar of liquid and see the light beam. This distinguishes a colloid from a solution.

21.2 Suspensions In a mixture called a suspension the particles can range widely in size. Muddy water, will settle when it is left still for a period of time.

21.2 Types of mixtures How can you tell the difference between a solution, a colloid and a suspension? First, try filtering it, then look for the Tyndall effect.

21.2 Water and solutions A solution contains at least two components: a solvent, and a solute. The solvent is the part of a mixture that is present in the greatest amount. Which of these is the solvent?

21.2 Water and solutions When the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

On the molecular level, dissolving of a solid (like sugar) occurs when molecules of solvent interact with and separate molecules of solute

21.2 Solubility The term solubility means the amount of solute (if any) that can be dissolved in a volume of solvent. Is there a limit for how much seltzer (solute) can dissolve in water (solvent)?

21.2 Solubility Chalk and talc do not have solubility values. These substances are insoluble in water because they do not dissolve in water.

21.2 Solubility A solution is saturated if it contains as much solute as the solvent can dissolve. Any solute added in excess of the substance’s solubility will not dissolve. What will happen to any un-dissolved gas when you unscrew the cap of seltzer water?

How much salt can dissolve in 200 mL of water at 25 °C? Solving Problems How much salt can dissolve in 200 mL of water at 25 °C? Looking for: …grams of solute Given … v = 200 mL; T = 25 C

Relationships: Solution Solubility table for reference Solving Problems Relationships: Solubility table for reference 35.9 g of salts in 100 mL water at 25 °C Solution …if there are 35.9 g salt/100 mL water, then “x” g/ 200 mL water = 71.8 g salts are need in 200 mL of water

21.2 Solubility A solution is saturated if it contains as much solute as the solvent can hold. An examples of a saturated solution is air. Air can be saturated with water. (We call it humidity!)

21.2 Solubility graphs Solubility values for three solutes are plotted in this temperature-solubility graph.

21.2 Solubility For something to dissolve in water, the water molecules need to break the bonds between the solute molecules. Water dissolves each substance differently because the chemical bond strengths between atoms found in different solutes are not the same.

21.2 Equilibrium When a solute like sugar is mixed with a solvent like water, two processes are actually going on continuously. Molecules of solute dissolve and go into solution. Molecules of solute come out of solution and become “un-dissolved.” When the rate of dissolving equals the rate of coming out of solution, we say equilibrium has been reached.

21.2 Equilibrium When a solution is unsaturated its concentration is lower than the maximum solubility. A supersaturated solution means there is more dissolved solute than the maximum solubility.

21.2 Solutions of gases and liquids Some solutions have a gas as the solute. In carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

21.2 Solutions of gases and liquids When temperature increases, the solubility of gases in liquid decreases.

21.2 Solutions of gases and liquids The variety and no. or organisms is controlled somewhat by the relationship between dissolved oxygen and temperature.

21.2 Solutions of gases and liquids The concentration of dissolved oxygen in water is important for fish and aquatic life.

21.2 Solutions of gases and liquids Oil and vinegar salad dressing separates because oil is not soluble in vinegar (mostly water). Liquids that are not soluble in water may be soluble in other solvents.

21.2 Solubility rules A set of solubility rules helps predict when an ionic compound is soluble or insoluble.