Solutions Chapter 22

How solutions form Solution-a mixture that appears the same throughout and is mixed at the molecular level. 1.solute- substance being dissolves 2.Solvent- substance doing the dissolving 3.Solutions can be liquids, gases or solids. 4.Alloys are solid solutions

How does dissolving happen? 1.Water molecules are polar- they have a positive are and a negative area. 2.Water molecules cluster around solid molecules, with their negative ends attracted to the positive ends of the solids. 3.Water molecules pull the solid particles in the solution. 4.The moving water molecules and solid molecules spread out and mix evenly to form a solution. 5.To mix solids to make an alloy solution, you must melt the solids.

Dissolving

Rate of dissolving depends on: 1. Stirring-speeds up dissolving by bringing more fresh solvent into contact with more solute. 2. Crystal size- dissolving occurs at the surface of a substance. Breaking a solid into pieces or powder increases its surface area, which speeds up dissolving. 3. Temperature- increasing the temperature of a solvent speeds up the movement of its particles. 4. To make a glass dissolve more quickly in a liquid, cool the liquid solvent and increase the pressure of the gas.

Solubility and concentration Solubility- the amount of substance that can dissolve in a solvent. Depends on the nature of the substance Solubilities of two substances can be compared by measuring.

Concentration A concentrated solution has a large amount of solute in the solvent. A dilute solution has a small amount of solute in the solvent. Concentrations can be expressed as percent by volume of the solute.

Types of solutions 1. Saturated solution- contains all the solute it can hold at a given temperature. -As temperature increases, the amount of solid solute that can dissolve in it increases. -Solubility curve- line on a graph used to figure how much solute can dissolve at any temperature on the graph.

Unsaturated solution- able to dissolve more solute at a given temperature. Super-saturated solution- contains more solute than a saturated one at the same temperature. -Made by raising temperature of a saturated solution, adding more solute, and lowering temperature back without disturbing the solution. -Unstable- Will crystallized if disturbed. -As it crystallizes, it gives off energy and produces heat.

You reach the bottom of a cup of hot chocolate and find globs of cocoa there. What does this tell you about your cup of hot chocolate? What can you do in the future to prevent this from happening?

Particles in solution Ions - particles with a charge Electrolytes- compounds that form charged particles (ions) and conduct electricity in water Non-electrolytes- substances that do not ionize in water and cannot conduct electricity.

How ions form 1.Ionization- molecules break apart in water, causing atoms to become ions by taking on a charge. 2.Dissociation- an ionic solid separates into its positive and negative ions.

Effects of solute particles All solute particles- polar, non-polar, electrolyte and non-electrolyte- affect the physical properties of the solvent. Adding solute to a solvent lowers the freezing point because the added solute particles interfere with the formation of the orderly freezing pattern. Adding a solute raises the boiling point because fewer solvent molecules can reach the surface and evaporate

Antifreeze

Dissolving without water Nonpolar materials have no positive or negative areas. They are not attracted to the polar water molecules, so they do not dissolve easily in water. Example- Oils(contain hydrocarbons) Large molecules of carbon and hydrogen atoms These atoms share electrons in an equal matter, so there is no positive or negative charge.

Why don’t oil spills in the ocean dissolve into the water?

Useful non-polar molecules Non-polar solvents dissolve nonpolar solutes. Many nonpolar solvents are toxic- dangerous to touch or inhale Soap- used for washing because it has polar and nonpolar properties.

Polarity and Vitamins B vitamins and vitamin C are polar- dissolve in the water in your body cells. Vitamin A is nonpolar- dissolves in fat of some body cells