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Acids and Bases

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					Acids and Bases


         An Introduction
           Chapter 7
What do you already know about
acids and bases?
What r some common acids?
 Deoxyribonucleaic acid (DNA)
 Ribonucleaic acid (RNA)
 Amino acids (building blocks of protein)
 Lactic acid (build-up →sore muscles; by-
 product of cell metabolism and insufficient
 oxygen)
 Boric acid (antiseptic)
 Acetic acid ( in vinegar)
 Citric acid (in fruits)
What is an acid?

 “an acid is a substance that produces
 hydrogen ions in solution” – Arrhenius
 1884
 HCl (aq) → H+ (aq) + Cl- (aq)
What r some common bases?

 Most soaps/detergents
 Most drain cleaners
 Most window cleaners
What is a base?

 “ a substance that produces
 hydroxide ions in solution” –
 Arrhenius
 NaOH (aq) →Na+ (aq) + OH- (aq)
Distinguishing between acids and
bases
 Most solutions of both acids and
 bases are clear and colourless.
 We need an indicator to tell them
 apart.
 An indicator is a chemical which
 changes colour as the concentration
 of H+ (aq) and OH- (aq) changes.
 Two common indicators are litmus
 and phenolpthalein
Which compounds are acids and
which are bases?
 Acids: Formulas begin with one or more
 hydrogen atoms (ex. HCl (aq) or H2SO4
 (aq))
  Names have the word “acid” in them (ex.
 Hydrochloric acid or sulfuric acid)
 Bases: Formulas end with one or more
 “OH” (ex. NaOH (aq) or Ca(OH)2 (aq))
 Names end in hydroxide (ex. Sodium
 hydroxide or calcium hydroxide)
Characteristics of acids
 Sour taste (never taste lab chemicals)
 Stinging feeling on mucous membranes
 Strong acids will burn your skin
 Aggressive reactions with metals
 Conduct electricity
 Turns blue litmus red
 Phenolpthalein remains colourless
 Forms carbon dioxide when reacting with
 carbonates and non metal oxides when
 reacting with water
Characteristics of bases
 taste bitter
 feel slippery (soap and many drugs are
 bases)
 caustic on organic matter
 conduct electricity
 Strong bases will burn your skin
 Turn red litmus blue
 Turns phenolpthalein pink
 Does not react with carbonates but forms
 metallic oxides when reacting with water
Oxides of Elements

 Acids and bases are formed when
 oxides of elements react with water.
 An oxide is a binary compound
 formed with an element and oxygen
 e.g. CO, CO2 , Al2O3, N2O5
 H2O (l) + CO2 (g) → H2CO3 (aq)
pH : a “powerful” scale ( courtesy of
Sørensen – a Danish biochemist)
 Really means the power or concentration
 of hydrogen ions in solution
 The lower the pH the greater the
 concentration of H+ (aq) and the more
 acidic the solution
 The higher the pH, the greater the
 concentration of OH- (aq) and the more
 basic the solution
 The scale goes from 0-14 with a midpoint
 of 7
 Solutions with a pH of 7 are neutral
Ways to measure pH

 pH paper
 pH meters
 pH probes
How is pH calculated?
 You need not know this but for future
 reference:
 pH = -log [H+]
 E.g. suppose that your concentration
 was 0.010 , enter this in your
 calculator and press the log button,
 change the sign, your answer should
 be 2.0
 Home work text p. 218 1-4, p. 225 1-5
Properties of Acids and Bases
 Two factors determine how many H+ ions are
 contained in a solution: concentration and
 percent ionization
 Concentration refers to the amount of pure acid
 dissolved per litre of water
 Percent ionization refers to the number of
 molecules that will ionize per 100 that dissolve.
 Strong acids ionize completely whereas weak
 acids do not. E.g. sulfuric is strong and acetic is
 weak
 Strong bases also ionize completely whereas
 weak bases do not e.g. NaOH is a strong base
 but NH3 is not
Strong Acids and Bases
Name                  Formula
Sulfuric acid         H2SO4
Hydrochloric acid     HCl
Nitric acid           HNO3
Carbonic acid         H2CO3
Sodium hydroxide      NaOH
Potassium hydroxide   KOH
Calcium hydroxide     Ca(OH)2
Magnesium hydroxide   Mg(OH)2
ammonia               NH3
Neutralization reactions
 When an acid and a base react together to
 form a new compound, the word equation
 is
 Acid + Base → Salt + Water
 A salt is an ionic compound produced
 when an acid and base react
 The reaction is also known as a
 neutralization reaction
 HNO3 (aq) + KOH (aq) → KNO3 (aq)+ H20
 (l)
Chemistry of Swimming Pools
 Acids, bases, and neutralization reactions help maintain
 water in swimming pools.
 Water is chlorinated to kill bacteria and algae but chlorine
 gas is toxic so we use sodium hypochlorite instead
 The following reactions describe how the pH of pools are
 adjusted
 HOCl (aq) +NaOH (aq) → NaOCl (aq) + H2O (l)
 NaOCl (aq) + H2O (l) →HOCl (aq) + Na+ (aq) + OH- (aq)
 HOCl (aq) → H+ (aq) + OCl- (aq)
 Acidic water may be neutralized by adding sodium carbonate
 Basic water may be neutralized by adding hydrochloric acid
Next up

 Acid Rain
 Purple Rain
 Rain on Me

				
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posted:4/23/2011
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