Many familiar compounds are acids or bases 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

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 of an acidic solution: 0 to < 7 …the closer its pH is to 0 pH of a neutral solution: = 7 pH of a basic solution: > 7 to 14 …the closer its pH is to 14 a solution with pH 3 is 103 = 1000 times more acidic than a solution with pH 6

litmus paper: blue = basic red = acidic 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 The blue paper changes color to red, indicating acidity somewhere between the pH range of 4.5 to 8.3 (however, note 8.3 is alkaline). Red litmus paper can indicate alkalinity with a color change to blue. In general, litmus paper is red below pH of 4.5 and blue above a pH of 8.3. Red paper that does not change color indicates the sample is an acid. Blue paper that does not change color indicates the sample is a base. If the paper turns purple, this indicates the pH is near neutral.

The chemical formula of an acid usually starts with hydrogen (H-) 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 "ate" means there is more oxygen in the anion than one ending in "ite" Examples: sulfate (SO42-) has more oxygen than sulfite (SO32-), nitrate (NO3-) has more oxygen in the anion than nitrite (NO2-)

-ate  -ic -ite  -ous 1. hydrogen + _____-ide = hydro_____-ic 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 "ate" means there is more oxygen in the anion than one ending in "ite" Examples: sulfate (SO42-) has more oxygen than sulfite (SO32-), nitrate (NO3-) has more oxygen in the anion than nitrite (NO2-)

HCl hydrogen chloride HCl (aq) hydrochloric acid HBr hydrogen bromide 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) hydrochloric acid HBr hydrogen bromide HBr (aq) hydrobromic acid HClO3 hydrogen chlorate HClO3 (aq) chloric acid HClO2 hydrogen chlorite HClO2 (aq) chlorous acid perchloric acid, has 1 more O atom in the anion than chloric acid hypochlorous acid, has 1 less O atom in the anion than chlorous acid

H2SO4 (aq) - _________________________ 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. sulphuric acid phosphoric acid carbonic acid

The chemical formula of a base usually ends with hydroxide (-OH) 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) NaOH(aq) = sodium hydroxide Mg(OH)2(aq) = magnesium hydroxide Ca(OH)2(aq) = calcium hydroxide NH4OH(aq) = ammonium hydroxide 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

we sometimes use the terms “basic” and “alkaline” interchangeably 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

feel** slippery (**never touch chemicals with your bare skin!) 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

taste* sour (*never put anything from the science lab in your mouth!) 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