Section 5.1 (not in notes. Sorry) Acids and Bases Section 5.1 (not in notes. Sorry)

Acids and Bases Acids and bases are very common. Acids and bases can be dangerous and corrosive! Never try to identify an acid or base by taste or touch!

pH Scale The strength of acids and bases is measured on the pH scale. pH below 7 is acidic pH 7 is neutral pH above 7 is basic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acids Neutral Bases Each decrease of 1 on the pH scale indicates 10x more acidic E.g., pH 3 is ten times more acidic than pH 4 pH 1 is 1000x more acidic than pH 4

pH The pH scale is based on powers of 10. A change in 1 pH unit represents a tenfold change in the acidity of a solution. For example, a solution with a pH of 1 is not twice as acidic as a solution with a pH of 2, but 10 times more acidic. Use the following to help you calculate the difference in pH. 10n, where n= the difference between the pH of two solutions Subtract the lower pH from the higher pH and multiply by -1. For example: (pH 5 - pH 7) x (-1) = 2 n=2 102 =10x10=100 Therefore, a solution with a pH of 5 is 102 or 100 times more acidic than a solution with a pH of 7.

Your turn With your shoulder partner, calculate 1.a solution with a pH of 3 and a solution with a pH of 1 2.a solution with a pH of 4 and a solution with a pH of 5 3.a solution with a pH of 2 and a solution with a pH of 6 4.a solution with a pH of 8 and a solution with a pH of 3 5.a solution with a pH of 13 and a solution with a pH of 1

pH Indicators 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 using electrical probes to measure how solutions conduct electricity pH indicators change colour based on the solution they are placed in Litmus paper is the most common indicator Two colours of litmus paper. Blue=basic and Red=acidic

Acids If you know a compound’s chemical formula, you may be able to identify it as an acid Acids often behave like acids only when dissolved in water Therefore, acids are often written with subscript (aq) = aqueous The chemical formula of an acid usually starts with hydrogen (H) Acids with a carbon usually have the C written first. HCl(aq) = hydrochloric acid, HNO3(aq) = nitric acid, CH3COOH(aq) = acetic acid

Naming Acids Hydrogen+…-ide = Hydro…ic acid Hydrogen+…-ate = …ic acid HF(aq) = hydrogen fluoride = hydrofluoric acd Hydrogen+…-ate = …ic acid H2CO3(aq) = hydrogen carbonate = carbonic acid Hydrogen+…-ite = …ous acid H2SO3(aq) = hydrogen sulphite=sulphurous acid

Some common acids Formula Common name Chemical name HF Hydrofluoric acid   HNO2 Nitrous acid HCl Hydrochloric acid HNO3 Nitric acid HBr Hydrobromic acid H2SO3 Sulfurous acid HI Hydroiodic acid H2SO4  Sulfuric acid H2CO3 Carbonic acid H3PO3 Phosphorous acid CH3COOH Acetic acid H3PO4  Phosphoric acid

The following gases are manufactured by dissolving a gas in water Acid Gas Formula Name HCl Hydrochloric acid   HNO3 Nitric acid NO2 H2SO3 Sulfurous acid SO2

Bases If you know a compound’s chemical formula, you may be able to identify it as a base Bases, like acids, often behave like bases only when dissolved in water Therefore, bases are often written with subscript (aq) = aqueous) The chemical formula of a base usually ends with hydroxide (-OH) Examples of common bases: NaOH(aq), Mg(OH)2(aq), Ca(OH)2(aq), NH4OH(aq)

Production of Ions Acids and bases can conduct electricity because they release ions in solution Acids release hydrogen ions, H+(aq) Bases release hydroxide ions, OH-(aq)

pH The pH of a solution refers to the concentration of ions it has. Square brackets are used to signify concentration, [H+(aq)], [OH-(aq)] High [H+(aq)] = low pH, very acidic High [OH-(aq)] = high pH, very basic A solution cannot have BOTH high [OH-(aq)] and [H+(aq)]; they cancel each other out and form water. This process is called neutralization H+(aq)+ OH-(aq) → H2O(l)