Acids and Bases

Properties of Acids tastes sour corrosive: react with certain metals to produce hydrogen gas React with bases, to produce water and a salt. turns blue litmus paper red

An acid is any substance that forms hydrogen ions (H+) in water. The H+ ion disassociates (separates from) whatever it is bonded to HCl water H+ + Cl-

Properties of Bases taste bitter slippery feel turns red litmus blue Reacts with acids to produce water and a salt.

A base is any substance that forms hydroxide ions (OH-) in water. The OH- ion disassociates (separates from) whatever it is bonded to NaOH water Na+ + OH-

Strengths of Acid & Bases Acids dissociate by donating hydrogen ions, and bases ionize by dissociating to form hydroxide ions. Some acids and bases either dissociate or ionize almost completely, and others do so only partially. Nearly complete dissociation is strong; partial dissociation is weak. Strong acids produce a lot of H+ Strong bases produce a lot of OH-

Strengths of Acid & Bases pH scale: numeric scale that measures the concentration of hydrogen ions. Ranges from 0-14. acid = 0 to <7. base = 7> to 14 When the pH is low, the concentration of H+ ions is high (acid) Pure H20 = pH 7.0 When the pH is high, the concentration of OH- is high (base)

Strengths of Acid & Bases The strength of an acid or a base can vary, depending on such conditions as temperature and concentration.

Indicators A pH indicator is a chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. the indicator causes the color of the solution to change depending on the pH.

Red Cabbage indicator Acidic or basic properties can be demonstrated by using extracted pigment from red cabbage as an indicator. When the indicator is added, basic solutions turn green. acidic solutions turn red.

When acids and bases are mixed together, the products are water and a salt. salts ionic compounds that can result from the neutralization reaction of an acid and a base.

Questions Describe the taste of acids and bases. acids sour, bases bitter What is a hydroxide ion made of? OH- What ions would you expect to find when an acid dissolves in water? H+ What ions would you expect to find when a base dissolves in water?

Questions If the pH of a solution is 6, would you expect to find more or fewer hydrogen ions (H+) than in a solution with a pH of 3? fewer Strong acids produce a lot of H+ Strong bases produce a lot of OH-

Chemical Thermodynamics Temperature: is a measure of the average kinetic energy of molecular motion in a sample (aka internal kinetic energy) Heat: is energy transferred from a sample at higher temperature to one at lower temperature.

Chemical Thermodynamics Endothermic processes: absorb heat, and their equations can be written with heat as a reactant. Exothermic processes: release heat, and their equations can be written with heat as a product.

The net heat released to or absorbed from the surroundings comes from the making and breaking of chemical bonds during a reaction breaking a bond always requires energy making a bond almost always releases energy. The amount of energy per bond depends on the strength of the bond.

Endothermic The products have more energy than the reactants, that energy is absorbed from the surroundings

Endothermic Endothermic processes absorb heat, and their equations can be written with heat as a reactant.

Exothermic The products have less energy than the reactants, that energy is released to the surroundings

Exothermic Exothermic processes release heat, and their equations can be written with heat as a product.

Physical changes are accompanied by changes in internal energy. What are the states of matter? solid liquid gas plasma

Physical changes are accompanied by changes in internal energy. Changes of physical state either absorb or release heat. Evaporation and melting require energy to overcome the bonds of attractions in the corresponding liquid or solid state. Condensation and freezing release heat to the surroundings as internal energy is reduced and bonds of attraction are formed.

Check for understanding the average kinetic energy of molecular motion in a sample is called Temperature The energy transferred from one object to another is heat A chemical process that absorbs heat is endothermic A chemical process that releases heat is exothermic

Check for understanding Breaking a chemical bond ______ energy requires Making a chemical bond _______ energy releases The amount of energy in a bond is related to the _______ of the bond. Strength

Check for understanding (releases, absorbs) Evaporation ______ energy absorbs Freezing _______ energy releases condensation _______ energy Melting _______ energy

Check for understanding Endothermic or exothermic?

Check for understanding Endothermic or exothermic?

Check for understanding Endothermic or exothermic?