ACIDS, BASES
AND SALTS
A guide for A level students
2008
KNOCKHARDY PUBLISHING
SPECIFICATIONS
KNOCKHARDY PUBLISHING
ACIDS, BASES AND SALTS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand
selected topics at AS and A2 level Chemistry. It is based on the requirements of the
AQA and OCR specifications but is suitable for other examination boards.
Individual students may use the material at home for revision purposes or it may be
used for classroom teaching if an interactive white board is available.
Accompanying notes on this, and the full range of AS and A2 topics, are available
from the KNOCKHARDY SCIENCE WEBSITE at...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either
clicking on the grey arrows at the foot of each page
or
using the left and right arrow keys on the keyboard
ACIDS AND BASES
BRØNSTED-LOWRY THEORY
ACID
proton donor
HCl ——> H+(aq) + Cl¯(aq)
BASE
proton acceptor
NH3 (aq) + H+(aq)
——>
NH4+(aq)
ACIDS AND BASES
BRØNSTED-LOWRY THEORY
ACID
proton donor
HCl ——> H+(aq) + Cl¯(aq)
BASE
proton acceptor
NH3 (aq) + H+(aq)
Conjugate systems
Acids are related to bases
ACID
Bases are related to acids
BASE
——>
PROTON
+
PROTON
NH4+(aq)
+
CONJUGATE BASE
CONJUGATE ACID
ACIDS AND BASES
BRØNSTED-LOWRY THEORY
ACID
proton donor
HCl ——> H+(aq) + Cl¯(aq)
BASE
proton acceptor
NH3 (aq) + H+(aq)
Conjugate systems
Acids are related to bases
ACID
Bases are related to acids
BASE
——>
NH4+(aq)
PROTON
+
PROTON
+
CONJUGATE BASE
CONJUGATE ACID
For an acid to behave as an acid, it must have a base present to accept a proton...
HA
acid
example
+
B
base
CH3COO¯ + H2O
base
acid
BH+
+
A¯
conjugate conjugate
acid
base
CH3COOH
acid
+
OH¯
base
STRONG ACIDS AND BASES
STRONG
ACIDS
e.g.
completely dissociate (split up) into ions in aqueous solution
HCl ——> H+(aq) + Cl¯(aq)
MONOPROTIC
1 replaceable H
DIPROTIC
2 replaceable H’s
HNO3 ——> H+(aq) + NO3¯(aq)
H2SO4 ——> 2H+(aq) + SO42-(aq)
STRONG ACIDS AND BASES
STRONG
ACIDS
e.g.
completely dissociate (split up) into ions in aqueous solution
HCl ——> H+(aq) + Cl¯(aq)
MONOPROTIC
1 replaceable H
DIPROTIC
2 replaceable H’s
HNO3 ——> H+(aq) + NO3¯(aq)
H2SO4 ——> 2H+(aq) + SO42-(aq)
STRONG
BASES
e.g.
completely dissociate into ions in aqueous solution
NaOH(aq)
——> Na+(aq) + OH¯(aq)
WEAK ACIDS
Weak acids
partially dissociate into ions in aqueous solution
e.g. ethanoic acid
When a weak acid dissolves in
water an equilibrium is set up
CH3COOH(aq)
HA(aq) + H2O(l)
CH3COO¯(aq)
HA(aq)
H+(aq)
A¯(aq) + H3O+(aq)
The water stabilises the ions
To make calculations easier
the dissociation can be written...
+
A¯(aq) +
H+(aq)
WEAK ACIDS
Weak acids
partially dissociate into ions in aqueous solution
e.g. ethanoic acid
CH3COOH(aq)
When a weak acid dissolves in
water an equilibrium is set up
HA(aq) + H2O(l)
CH3COO¯(aq)
The weaker the acid
HA(aq)
H+(aq)
A¯(aq) + H3O+(aq)
The water stabilises the ions
To make calculations easier
the dissociation can be written...
+
A¯(aq) +
H+(aq)
the less it dissociates
the more the equilibrium lies to the left.
WEAK BASES
Partially react with water to give ions in aqueous solution
e.g. ammonia
When a weak base dissolves in water an equilibrium is set up
NH3 (aq)
+ H2O (l)
NH4+ (aq) + OH¯ (aq)
as in the case of acids it is more simply written
NH3 (aq) +
H+ (aq)
NH4+ (aq)
WEAK BASES
Partially react with water to give ions in aqueous solution
e.g. ammonia
When a weak base dissolves in water an equilibrium is set up
NH3 (aq)
+ H2O (l)
NH4+ (aq) + OH¯ (aq)
as in the case of acids it is more simply written
NH3 (aq) +
The weaker the base
H+ (aq)
NH4+ (aq)
the less it dissociates
the more the equilibrium lies to the left
The relative strengths of bases can be expressed as Kb or pKb values.
REACTIONS OF HYDROCHLORIC ACID
Is a typical acid in dilute aqueous solution
Hydrogen chloride is a colourless
covalent gas; it is a poor conductor
of electricity because there are no
free electrons or ions present. It
has no action on dry litmus paper
because there are no aqueous
hydrogen ions present.
HCl
——> H+ (aq)
+ Cl¯(aq)
REACTIONS OF HYDROCHLORIC ACID
Is a typical acid in dilute aqueous solution
Hydrogen chloride is a colourless
covalent gas; it is a poor conductor
of electricity because there are no
free electrons or ions present. It
has no action on dry litmus paper
because there are no aqueous
hydrogen ions present.
HCl
——> H+ (aq)
+ Cl¯(aq)
If the gas is passed into water, the
hydrogen chloride molecules dissociate
into ions. The solution now conducts
electricity showing ions are present. For
each hydrogen chloride molecule that
dissociates one hydrogen ion and one
chloride ion are produced. The solution
turns litmus paper red because of the
H+(aq) ions.
REACTIONS OF HYDROCHLORIC ACID
Is a typical acid in dilute aqueous solution
Hydrogen chloride is a colourless
covalent gas; it is a poor conductor
of electricity because there are no
free electrons or ions present. It
has no action on dry litmus paper
because there are no aqueous
hydrogen ions present.
HCl
——> H+ (aq)
+ Cl¯(aq)
If the gas is passed into water, the
hydrogen chloride molecules dissociate
into ions. The solution now conducts
electricity showing ions are present. For
each hydrogen chloride molecule that
dissociates one hydrogen ion and one
chloride ion are produced. The solution
turns litmus paper red because of the
H+(aq) ions.
REACTIONS OF HYDROCHLORIC ACID
Is a typical acid in dilute aqueous solution
HYDROGEN CHLORIDE
colourless gas
covalent molecule
HCl(g)
poor
no reaction
HCl
——> H+ (aq)
+ Cl¯(aq)
HYDROCHLORIC ACID
Appearance
Bonding
Formula
Conductivity
Dry blue litmus
colourless soln.
aqueous ions
HCl(aq)
good
goes red
REACTIONS OF HYDROCHLORIC ACID
Is a typical acid in dilute aqueous solution
HCl
——> H+ (aq)
+ Cl¯(aq)
Hydrogen chloride is a colourless
covalent gas; it is a poor conductor
of electricity because there are no
free electrons or ions present. It
has no action on dry litmus paper
because there are no aqueous
hydrogen ions present.
hydrogen chloride
hydrochloric acid
Appearance
colourless gas
colourless soln.
If the gas is passed into water, the
hydrogen chloride molecules dissociate
into ions. The solution now conducts
electricity showing ions are present. For
each hydrogen chloride molecule that
dissociates one hydrogen ion and one
chloride ion are produced. The solution
turns litmus paper red because of the
+(aq)
ions.
Bonding H
and
formula
Conductivity
Dry litmus
covalent molecule HCl(g)
aqueous ions HCl(aq)
poor
good
no reaction
goes red
REACTIONS OF HYDROCHLORIC ACID
Metals
magnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen
Mg(s)
1.
+
2HCl(aq)
——>
MgCl2(aq)
WRITE OUT THE BALANCED EQUATION FOR THE REACTION
+
H2(g)
REACTIONS OF HYDROCHLORIC ACID
Metals
magnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen
Mg(s)
Mg(s)
1.
2.
+
+
2HCl(aq)
2H+(aq) + 2Cl¯(aq)
——>
——>
MgCl2(aq)
+
H2(g)
Mg2+(aq) + 2Cl¯(aq) + H2(g)
WRITE OUT THE BALANCED EQUATION FOR THE REACTION
DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T
REACTIONS OF HYDROCHLORIC ACID
Metals
magnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen
Mg(s)
Mg(s)
+
+
2H+(aq) + 2Cl¯(aq)
cancel ions
1.
2.
3.
——>
2HCl(aq)
Mg(s)
——>
+ 2H+(aq)
MgCl2(aq)
+
H2(g)
Mg2+(aq) + 2Cl¯(aq) + H2(g)
——>
Mg2+(aq) +
H2(g)
WRITE OUT THE BALANCED EQUATION FOR THE REACTION
DILUTE ACIDS AND SALTS CONTAIN IONS; WATER, HYDROGEN & CARBON DIOXIDE DON’T
CANCEL OUT THE IONS WHICH APPEAR ON BOTH SIDES OF THE EQUATION
REACTIONS OF HYDROCHLORIC ACID
Metals
magnesium + dil. hydrochloric acid ——> magnesium chloride + hydrogen
Mg(s)
Mg(s)
+
+
2H+(aq) + 2Cl¯(aq)
cancel ions
Basic
Oxides
Mg(s)
copper(II) oxide
CuO(s)
Cu2+O2-(s)
——>
2HCl(aq)
+
+
+ 2H+(aq)
2HCl(aq)
——>
+
——>
——>
Mg2+(aq) +
CuCl2(aq)
——>
H2(g)
copper(II) chloride + water
——> Cu 2+ (aq) + 2Cl¯(aq)
O2- + 2H+(aq)
H2(g)
Mg2+(aq) + 2Cl¯(aq) + H2(g)
dil. hydrochloric acid
+ 2H+(aq) + 2Cl¯(aq)
cancel ions
——>
MgCl2(aq)
H2O(l)
+
+
H2O(l)
H2O(l)
REACTIONS OF HYDROCHLORIC ACID
Alkalis
sodium hydroxide + dil. hydrochloric acid
NaOH(aq)
Na+(aq) + OH¯(aq)
cancel ions
+
HCl(aq)
+ H+(aq) + Cl¯(aq)
——>
——> sodium chloride + water
NaCl(aq)
+
——> Na+ (aq) + Cl¯(aq)
H+(aq) + OH¯(aq)
——>
H2O(l)
H2O(l)
+
H2O(l)
REACTIONS OF HYDROCHLORIC ACID
Alkalis
——> sodium chloride + water
sodium hydroxide + dil. hydrochloric acid
NaOH(aq)
Na+(aq) + OH¯(aq)
cancel ions
Carbonates
+
HCl(aq)
+ H+(aq) + Cl¯(aq)
——>
NaCl(aq)
+
H2O(l)
——> Na+ (aq) + Cl¯(aq)
——>
H+(aq) + OH¯(aq)
+
H2O(l)
H2O(l)
calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water
CaCO3(s)
+
2HCl(aq)
Ca2+CO32-(s) + 2H+(aq) + 2Cl¯(aq)
cancel ions
——>
CaCl2(aq)
+
CO2(g) + H2O(l)
——> Ca2+(aq) + 2Cl¯(aq) + CO2(g) + H2O(l)
CO32- + 2H+(aq)
——>
CO2(g) + H2O(l)
REACTIONS OF HYDROCHLORIC ACID
Alkalis
——> sodium chloride + water
sodium hydroxide + dil. hydrochloric acid
NaOH(aq)
Na+(aq) + OH¯(aq)
cancel ions
Carbonates
+
HCl(aq)
+ H+(aq) + Cl¯(aq)
——>
NaCl(aq)
+
H2O(l)
——> Na+ (aq) + Cl¯(aq)
——>
H+(aq) + OH¯(aq)
+
H2O(l)
H2O(l)
calcium carbonate + hydrochloric acid ——> calcium chloride + carbon dioxide + water
CaCO3(s)
+
2HCl(aq)
Ca2+CO32-(s) + 2H+(aq) + 2Cl¯(aq)
cancel ions
Hydrogen carbonates
——>
CaCl2(aq)
+
CO2(g) + H2O(l)
——> Ca2+(aq) + 2Cl¯(aq) + CO2(g) + H2O(l)
CO32- + 2H+(aq)
——>
H+(aq) + HCO3¯ ——>
CO2(g) + H2O(l)
CO2(g)
+
H2O(l)
REACTIONS OF HYDROCHLORIC ACID
SUMMARY
METALS
react to give
a salt + hydrogen
METAL OXIDES
react to give
a salt + water
METAL HYDROXIDES
react to give
a salt + water
CARBONATES
react to give
a salt + water + carbon dioxide
HYDROGENCARBONATES
react to give
a salt + water + carbon dioxide
AMMONIA
reacts to give
an ammonium salt
ACIDS, BASES
AND SALTS
THE END
© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING