(c) McGraw Hill Ryerson 2007 Many familiar compounds are acids or bases. –Lemon juice, soap, oranges, pop… Acids and bases can be very dangerous. –Both can be very corrosive. NEVER try to identify an acid or base by taste or touch! See pages

(c) McGraw Hill Ryerson 2007 The strength of acids and bases is measured on the pH scale. –pH below 7 = acidic –pH above 7 = basic –pH 7 = neutral – Acids Neutral Bases See pages

Acids release __________ into a solution. Bases release _________ into a solution. [ H + ] [OH - ]

pH pH is the concentration of ____ expressed as a logarithm. Every change in the pH scale of one unit is a change in ______ times the concentration of H+. Example: pH 4 is 10X more acidic than pH 5. pH 3 is 1000X more acidic than pH 5. [ H + ] 10

pH of 0 to 6.9 Contribute H + ions into a solution Turn litmus paper RED Conduct ELECTRICITY Produce H + gas (when added to some metals) Are CORROSIVE

(c) McGraw Hill Ryerson 2007 Acids often behave like acids only when dissolved in water. Therefore, acids often are written with symbol (aq) = aqueous = water. The chemical formula of an acid usually starts with hydrogen (H). –HCl (aq) = hydrochloric acid, HNO 3(aq) = nitric acid Acids with a carbon usually have the C written first. CH 3 COOH (aq) = acetic acid See pages

(c) McGraw Hill Ryerson 2007 Naming acids: If you know a compound’s chemical formula, you may be able to identify whether it as an acid. –Hydrogen + …-ide = hydro…ic acid HF (aq) = hydrogen fluoride = hydrofluoric acid –Hydrogen + …-ate = …ic acid H 2 CO 3(aq) = hydrogen carbonate = carbonic acid –Hydrogen + …-ite = …ous acid H 2 SO 3(aq) = hydrogen sulphite = sulphurous acid See pages Sulfuric acid is used in batteries.

pH of 7.1 to 14 Donate [OH] - ions into a solution [OH-] The hydroxide [OH-] group is neutralized by a hydrogen ion and water is formed. Turns litmus paper BLUE Conduct ELECTRICITY Are Slippery Are CAUSTIC

(c) McGraw Hill Ryerson 2007 Bases often behave like bases only when dissolved in water. Therefore, bases often are written with symbol (aq) = aqueous = water. If you know a compound’s chemical formula, you may be able to identify it as a base. The chemical formula of a base usually ends with hydroxide (OH).

(c) McGraw Hill Ryerson 2007 Bases can be gentle or very caustic. Examples of common bases: –NaOH (aq) –Mg(OH) 2(aq) –Ca(OH) 2(aq) –NH 4 OH (aq) See page 227

The pH of almost all living systems is between pH ________. Maintaining the proper pH then is vital living systems. pH is very important to the environment as well: acid rain agriculture 6 - 8

Hydrangea in acidic soilHydrangea in basic soil

(c) McGraw Hill Ryerson 2007 The pH of acids and bases cannot be determined by sight. –Instead, pH is measured by other chemicals called indicators OR by a pH meter that measures the electrical conductivity of the solution. pH indicators change colour based on the solution they are placed in. –Litmus paper is the most common indicator. There are 2 colours of litmus paper: –Blue = basic (pH above 7) –Red = acidic (pH below 7) Litmus paper

(c) McGraw Hill Ryerson 2007 –A universal indicator contains many indicators that turn different colours at different pH values can be in liquid form, or on paper strips like litmus. –Indicators change colour at different pH values, so different indicators are used to identify different pH values. Bromothymol blue for pH 6 – 7.6, phenolphthalein for pH 8.2 – 10. Many natural sources, such as beets, blueberries, cabbage, pansy flower petals... are also indicators. See pages

Cabbage Juice paper in baking soda (BASE) Cabbage Juice paper in lemon juice (ACID)

(c) McGraw Hill Ryerson 2007 Acids and bases can conduct electricity because they release ions in solution. – Acids release hydrogen ions, H +. – Bases release hydroxide ions OH –. The pH of a solution refers to the concentration of HYDROGEN ions it has. – Square brackets are used to signify concentration, [H + ], [OH – ] High [H + ] = low pH, very acidic High [OH – ] = high pH, very basic See page 228

– A solution cannot have BOTH high [H + ] and [OH – ]; they cancel each other out and form water. – This process is called neutralization. – H + + OH –  H 2 OORH + + OH –  HOH See page 228 NEUTRALIZATION:

In water, the concentration of H + is equal to the concentration of OH -. By definition, pure water is ______________________ A solution is ACIDIC if the _______________ A solution is BASIC if the ________________ [ H + ] = [OH - ] NEUTRAL [ H + ] > [OH - ] [ H + ] < [OH - ]

(c) McGraw Hill Ryerson 2007 See page 229