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 compounds 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: 1-7 the more acidic a solution, the closer its pH is to 1
pH of a neutral solution: 7 pH of a basic solution: 7-14 the more basic a solution, the closer its pH is to 14 1 unit of change on the pH scale = 10 times change in the degree of acidity / basicity Ex. a solution with pH 4 is 101 = 10 times more acidic than a solution with pH 5 Ex. a solution with pH 3 is 103 = 1000 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, HNO3(aq) = nitric acid
Acids with a carbon usually have the C written first CH3COOH(aq) = acetic acid Naming Acids -ate -ic -ite -ous 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 H2CO3 = hydrogen carbonate H2CO3(aq) = carbonic acid 3. hydrogen + _____-ite = _______-ous acid H2SO3 = hydrogen sulphite H2SO3(aq) = sulphurous acid
Naming Acids Note how the names can change with the addition of (aq). Formula Chemical Name Formula in Solution Chemical Name can be changed to... HCl hydrogen chloride HCl (aq)
chloric acid HClO2 hydrogen chlorite HClO2 (aq) chlorous acid Some Common Acids HNO3 (aq) nitric acid H2SO4 (aq) - _________________________ H3PO4 (aq) - _________________________ H2CO3 (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. 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) NH4OH(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) H2O( ) 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 + 2H2O Ca(OH)2 + H2 (-OH) signifies a base See page 227 (c) McGraw Hill Ryerson 2007 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 http://www.brainpop.com/science/matterandchemistry/acidsandbases/ http://www.bcscience.com/bc10/pgs/quiz_section5.1.htm
Acknowledgements . We are grateful for support from the Office of Student Creative Activities and Research (OSCAR) and University Life. We also appreciate the support from the Mason Community for this ongoing work.
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