Section 1: How Solutions Form

• What is a solution?

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

• Solutes and Solvents

  • In a solution, one substance is dissolved in another.

    • Solute: the 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.

    • Aqueous Solution: A solution in which water is the solvent

    • Solutions also can be gaseous or even solid.

• How Substances Dissolve

  • Fruit drinks and sports drinks are examples of solutions made by dissolving solids in liquids.

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

  • Particles of liquids and gases move much more freely than do particles of solids. 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

  • When two substances form a solution, the dissolving occurs at different rates.

  • Sometimes the rate at which a solute dissolves into a solvent is fast, while other times it is slow.

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

  • Another way to speed the dissolving of a solid in a liquid is to grind large crystals into smaller ones.

  • Crystal size affects solubility. Large crystals dissolve in water slowly.

  • 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.

  • In addition to stirring and decreasing particle size, a third way to increase the rate at which most solids dissolve is to increase the temperature of the solvent.

  • 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 solute that can dissolve in a solvent depends on the nature of these substances.

• Concentration: describes how much solute is present in a solution compared to the amount of solvent.

  • 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.

  • Concentrations of solutions can be described precisely

    • One way is to state the percentage by volume of the solute.

    • Concentrations commonly range from 10 percent to 100 percent juice.

• Types of Solutions

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

  • Generally, 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 determine 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.

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

    • A supersaturated solution is unstable.

• Solubility of Gases

  • Solutions of gases behave differently from those of solids or liquids. This soda is bottled under pressure to keep carbon dioxide in solution. When the bottle is opened, pressure is released and carbon dioxide bubbles out of solution.

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

Section 3: Acids, Bases, and Salts

• Acid: a substance that produces hydrogen ions in a water solution.

  • Although some acids can burn and are dangerous to handle, most acids in foods are safe to eat.

  • Acids have several common properties.

    • All acids taste sour.

    • Some acids can damage tissue by producing painful burns

    • Acids are corrosive.

    • Acids also react with indicators to produce predictable changes in color.

  • Indicator: an organic compound that changes color in acids and bases.

  • Many foods contain acids.

  • When sulfuric acid is added to sugar, the mixture foams, removing hydrogen and oxygen atoms as water and leaving air-filled carbon.

• Base: Any substance that forms hydroxide ions, OH-, in a water solution; any substance that accepts H􏰅 from acids.

  • One characteristic of bases is that they feel slippery, like soapy water.

  • Bases are important in many types of cleaning materials.

  • Bases are important in industry, also.

  • One way to think about bases is as the complements, or opposites, of acids.

  • In the pure, undissolved state, many bases are crystalline solids.

  • In solution, bases feel slippery and have a bitter taste.

  • Like strong acids, strong bases are corrosive, and contact with skin can result in severe burns.

  • Taste and touch never should be used to test for the presence of a base or an acid.

  • Like acids, bases react with indicators to produce changes in color. The indicator litmus turns blue in bases.

• Solutions of Acids and Bases

  • When an acid dissolves in water, the negative areas of nearby water molecules attract the positive hydrogen in the acid.

  • Dissociation is the process in which an ionic solid separates into its positive and negative ions.

  • When acids and bases are dissolved in water, they produce ions. Acids produce hydronium ions in water. Bases produce hydroxide ions in water.

  • Compounds that can form hydroxide ions (OH–) in water are classified as bases.

  • When bases that contain –OH dissolve in water, the negative areas of nearby water molecules attract the positive ion in the base.

  • Too much acid can produce discomfort.

  • Neutralization is a chemical reaction between an acid and a base that takes place in a water solution.

  • The acid-base equation accounts for only half of the ions in the solution. The remaining ions react to form a salt.

    • A salt is a compound formed when the negative ions from an acid combine with the positive ions from a base

  • Ammonia is a base that does not contain -OH.

  • A reaction between sodium hypochlorite and ammonia produces the toxic gases hydrazine and chloramine.

  • The reactions of acids and bases are important to the chemistry of living systems, the environment, and many industrial processes.

Section 4: Strength of Acids and Bases

• Strong and Weak Acids and Bases

  • Some acids must be handled with great care.

  • One measure of acid strength is the ability to dissociate in solution.

  • Strong Acid: When it dissolves in water, almost 100 percent of the acid molecules dissociate into ions.

  • Weak Acid: When it dissolves in water, only a small fraction of the acid molecules dissociates into ions.

  • Ions in solution can conduct an electric current are called electrolytes.

  • The more ions a solution contains, the more current it can conduct.

  • In strong acids, such as HCl, nearly all the acid dissociates.

  • Strong Base: dissociates completely in solution.

  • Weak Base: one that does not dissociate completely.

    • Because ammonia produces only a few ions and most of the ammonia remains in the form of NH3, ammonia is a weak base.

• The terms strong and weak are used to classify acids and bases. The terms refer to the ease with which an acid or base dissociates in solution.

• The terms dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution.

• pH of a Solution

  • pH: measure of the concentration of H+ ions in it.

  • The pH measures how acidic or basic a solution is.

  • Solutions with a pH lower than 7 are described as acidic, and the lower the value is, the more acidic the solution is.

  • Solutions with a pH greater than 7 are basic, and the higher the pH is, the more basic the solution is.

  • A solution with a pH of exactly 7 indicates that the concentrations of H+ ions and OH- ions are equal.

  • The pH of a sample can be measured in several ways. Indicator paper gives an approximate value quickly, however, a pH meter is quick and more precise.

• Blood pH

  • Your blood circulates throughout your body carrying oxygen, removing carbon dioxide, and absorbing nutrients from food that you have eaten.

    • In order to carry out its many functions properly, the pH of blood must remain between 7.0 and 7.8.

  • Buffers are solutions containing ions that react with additional acids or bases to minimize their effects on pH.

  • Buffers help keep your blood close to a nearly constant pH of 7.4.