Section 1: How Solutions Form

• What is a solution?

  • Solution: a mixture that has the same composition, color, density, and even taste throughout.

  • Liquid solutions may contain gases, other liquids, or solids.

• Solutes and Solvents

  • Solute: substance being dissolved.

  • Solvent: the substance doing the dissolving.

  • When a solid dissolves in a liquid, the solid is the solute and the liquid is the solvent.

  • When a liquid dissolves in another liquid, the substance present in the larger amount is usually called the solvent.

  • Solutions can also be gaseous or even solid.

• How Substances Dissolve

  • The dissolving of a solid in a liquid occurs at the surface of the solid.

  • Polar: water molecules have a positive area and a negative area.

  • When gases dissolve in gases or when liquids dissolve in liquids, this movement spreads solutes evenly throughout the solvent, resulting in a homogenous solution.

  • Although solid particles do move a little, this movement is not enough to spread them evenly throughout the mixture.

• Rate of Dissolving

  • If two substances will form a solution, they will do so at a particular rate.

  • There are several things you can do to speed up the rate of dissolving—stirring, reducing crystal size, and increasing temperature are three of the most effective techniques.

    • Stirring a solution speeds up dissolving because it brings more fresh solvent into contact with more solute.

    • Breaking the solid into smaller pieces greatly increases its surface area. Because dissolving takes place at the surface of the solid, increasing the surface area allows more solvent to come into contact with more solid solute.

    • Increasing the temperature of a solvent speeds up the movement of its particles. This increase causes more solvent particles to bump into the solute.

    • Knowing how much each technique affects the rate will allow you to control the rate of dissolving more precisely.

Section 2: Solubility and Concentration

• How much can dissolve?

  • Solubility: the maximum amount of a solute that can be dissolved in a given amount of solvent at a given temperature.

  • The amount of a substance that can dissolve in a solvent depends on the nature of these substances.

  • For solutes that are gases, the pressure also must be given.

• Concentration

  • A concentrated solution is one in which a large amount of solute is dissolved in the solvent.

  • A dilute solution is one that has a small amount of solute in the solvent.

  • If two or more liquids are being mixed, the concentration is given in percentage by volume.

• Types of Solutions

  • Saturated Solution: a solution that contains all the solute it can hold at a given temperature.

    • As the temperature of a liquid solvent increases, the amount of solid solute that can dissolve in it also increases.

  • You can use a solubility curve to figure out how much solute will dissolve at any temperature given on the graph.

  • Unsaturated Solution: any solution that can dissolve more solute at a given temperature.

    • Each time a saturated solution is heated to a higher temperature, it becomes unsaturated.

  • At the lower temperature, the solvent cannot hold as much solute.

  • Supersaturated Solution: one that contains more solute than a saturated solution at the same temperature. Supersaturated solutions are unstable.

  • Energy is given off as new bonds form between the ions and the water molecules.

  • Some substances, such as ammonium nitrate, must draw energy from the surroundings to dissolve.

• Solubility of Gases

  • Shaking or pouring a solution of a gas in a liquid causes gas to come out of solution. Agitating the solution exposes more gas molecules to the surface, where they escape from the liquid.

  • Soft drinks are bottled under increased pressure. This increases the amount of carbon dioxide that dissolves in the liquid. When the pressure is released, the carbon dioxide bubbles out.

  • Another way to increase the amount of gas that dissolves in a liquid is to cool the liquid.

Section 3: Particles in Solution

• Particles with a Charge

  • Ions: charged particles

  • Electrolytes: The compounds that produce solutions of ions that conduct electricity in water.

  • Some substances, like sodium chloride, are strong electrolytes and conduct a strong current.

    • Strong electrolytes exist completely in the form of ions in solution.

  • Non-electrolytes: Substances that form no ions in water and cannot conduct electricity

  • Ionization: The process of forming ions

  • Dissociation: The process in which an ionic solid.

• Effects of Solute Particles

  • All solute particles—polar and non-polar, electrolyte and non-electrolyte—affect the physical properties of the solvent, such as its freezing point and its boiling point.

  • The effect that a solute has on the freezing point or boiling point of a solvent depends on the number of solute particles in solution, not on the chemical nature of the particles.

  • As a substance freezes, its particles arrange themselves in an orderly pattern. The added solute particles interfere with the formation of this pattern, making it harder for the solvent to freeze. To overcome this interference, a lower temperature is needed to freeze the solvent.

  • Certain animals that live in extremely cold climates have their own kind of antifreeze.

  • The amount the boiling point is raised depends upon the number of solute molecules present.

  • Solute particles interfere with the evaporation of solvent particles. Thus, more energy is needed for the solvent particles to escape from the liquid surface, and so the boiling point of the solution will be higher than the boiling point of solvent alone.

  • Solute particles raise the boiling point of a solution.

Section 4: Dissolving Without Water

• When Water Won’t Work

  • Water often is referred to as the universal solvent because it can dissolve so many things.

  • Non-polar Materials: have no separated positive and negative areas.

    • Non-polar materials do not dissolve in water except to a small extent, if at all.

  • Most salad oils contain large molecules made of carbon and hydrogen atoms, which are called hydrocarbons.

    • In hydrocarbons, carbon and hydrogen atoms share electrons in a nearly equal manner.

  • Some substances form solutions with polar as well as non-polar solutes because their molecules have a polar and a non-polar end.

    • The polar end dissolves polar substances, and the non-polar end dissolves non-polar substances.

• Useful Non-polar Molecules

  • Some materials around your house may be useful as non- polar solvents.

  • Molecules of a non-polar solute can slip easily among molecules of a non-polar solvent.

  • Many non-polar solvents are connected with specific jobs.

  • Soap has an ionic end that will dissolve in water and a long hydrocarbon portion that will dissolve in oily dirt.

• Polarity and Vitamins

  • Some fat-soluble vitamins are toxic in high concentrations, so taking large doses or taking doses that are not recommended by your physician can be dangerous.

  • Other vitamins, such as vitamins B and C, are polar com- pounds.

  • Polar vitamins dissolve readily in the water that is in your body.

  • The best way to stay healthy is to eat a variety of healthy foods. Such a diet will supply the vitamins you need with no risk of overdoses.