5.1 - Acids and Bases Many familiar compounds are acids or bases Classification as acid or base is based on chemical composition  If you know a compound’s chemical formula, you may be able to identify it as an acid / base *Acids and bases can be very dangerous*  They can be very corrosive (in the case of a strong acid) or caustic (in the case of a strong base)  NEVER try to identify an acid or base by taste or touch

pH Scale the strength of acids & bases in measured on the pH scale  pH of an acidic solution: _____________  the more acidic a solution, the closer its pH is to _____  pH of a neutral solution: _____________  pH of a basic solution: _____________  the more basic a solution, the closer its pH is to _____ 1 unit of change on the pH scale = 10 times change in the degree of acidity / basicity  Ex. a solution with pH 4 is 10 1 = 10 times more acidic than a solution with pH 5  Ex. a solution with pH 3 is _______________ times more acidic than a solution with pH 6

pH Indicators pH indicators are chemicals that change colour depending on the acidity / basicity of the solution in which they are placed  litmus paper: blue = basic red = acidic  Why should you use both blue and red litmus when testing a solution? A pH meter uses probes to measure the electrical conductivity of a solution 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 (ie. beets and cabbage) are indicators

Acids Acids are often written with subscript (aq) = aqueous, since they often must be dissolved in water to behave like acids 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

Naming Acids 1.hydrogen + _____-ide = hydro_____-ic acid HF = hydrogen fluoride  if no state of matter is given, start name with “hydrogen” HF (aq) = hydrofluoric acid 2.hydrogen + _____-ate = ________-ic acid H 2 CO 3 = hydrogen carbonate H 2 CO 3(aq) = carbonic acid 3.hydrogen + _____-ite = _______-ous acid H 2 SO 3 = hydrogen sulphite H 2 SO 3(aq) = sulphurous acid -ate  -ic -ite  -ous

Naming Acids – Note how the names can change with the addition of (aq). FormulaChemical NameFormula in Solution Chemical Name can be changed to... HClhydrogen chlorideHCl (aq)hydrochloric acid HBrhydrogen bromideHBr (aq)hydrobromic acid HClO 3 hydrogen chlorateHClO 3 (aq)chloric acid HClO 2 hydrogen chloriteHClO 2 (aq)chlorous acid

Some “Common” Acids HNO 3 (aq) – nitric acid H 2 SO 4 (aq) - _________________________ H 3 PO 4 (aq) - _________________________ H 2 CO 3 (aq) - _________________________ Knowing these acids can help you recall the combining capacities of their polyatomic ions - YAY!! Use the reverse cross rule and the fact that the hydrogen ion has an ion charge of +1.

(c) McGraw Hill Ryerson 2007 Bases Bases are often written with subscript (aq) = aqueous, since they often must be dissolved in water to behave like bases 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)  NH 4 OH (aq) See page 227

(c) McGraw Hill Ryerson 2007 Production of Ions Acids and bases can conduct electricity because they release ions in solution.  Acids release H + (aq) ions  Bases release OH – (aq) ions The pH of a solution refers to the concentration of ions it has.  Square brackets signify concentration: [H + (aq) ], [OH – (aq) ]  High [H + (aq) ] = low pH, very acidic  High [OH – (aq) ] = high pH, very basic H + and OH – ions readily react with each other, so a solution cannot be both acidic and basic at the same time. They cancel each other out and form water in a process called neutralization.  H + (aq) + OH – (aq)  H 2 O ( ) See page 228

(c) McGraw Hill Ryerson 2007 Basic = “alkaline” we sometimes use the terms “basic” and “alkaline” interchangeably alkaline earth metals (ie. Ca, Mg, …) combine with water to produce basic solutions… Ex. Ca + 2H 2 O  Ca(OH) 2 + H 2 (-OH) signifies a base See page 227

Properties of Bases taste* bitter (*never put anything from the science lab in your mouth!) feel** slippery (**never touch chemicals with your bare skin!) many bases are caustic – burn skin no reaction with metal conduct electricity have a pH greater than 7 turn red litmus paper blue phenolphthalein is pink in a basic solution form OH - (aq) (hydroxide) ions in solution chemical formula of a base usually ends with OH

Properties of Acids taste* sour (*never put anything from the science lab in your mouth!) many acids are corrosive – burn skin** & “eat through” metal (**never touch chemicals with your bare skin!) conduct electricity have a pH less than 7 turn blue litmus paper red phenolphthalein is colourless in an acidic solution form H + (aq) (hydrogen) ions in solution chemical formula of an acid usually starts with H