Transcript Acids and Bases

Acids and Bases
An Introduction
Chapter 4
Nova Scotia Science 10
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; byproduct 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 are 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
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
Sulfuric acid
Hydrochloric acid
Formula
H2SO4
HCl
Nitric acid
Carbonic acid
Sodium hydroxide
Potassium hydroxide
Calcium hydroxide
Magnesium hydroxide
ammonia
HNO3
H2CO3
NaOH
KOH
Ca(OH)2
Mg(OH)2
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
HOCl (aq) +NaOH (aq) → NaOCl (aq)
+ H2O (l) and