Ionic Equations
and
State Symbols
There are 2 types of equations:
(1)Molecular: shows full numbers of reactants
(2) Ionic: shows only reacting ions.
To balance an equation numbers or co-efficients
are placed at the front of
the formula of each compound, element or ion.
Compounds have a fixed and definite formula and
should not be changed to balance the equation!
e.g Hydrogen combines with Oxygen to
produce water.
2H + O
2HO
2
The above equation is balanced as it has
equal amounts of reactens and products but is not
correct because the chemical formula of water is
not correct.
To balance an equation the quantitiy of
whole molecoles or ions should be varied
until there are equal numbers of each
element on both sides of the equation.
The chemical formula has not been changed.
1. 2H + O2
H2O
There are more reactenthan products present.
2. There are more products than reactants.
2H
+
O2
2H2O
3. The equation below is properly balanced.
Notice, the chemical
formula of the compound
has not changed. Water is
still H2O and Oxygen is
still O2.
State Symbols:
There are 4 state symbols, to describe the
conditions of each
substance of an equation:
(s) - denotes a solid
(l) - denotes a liquid(H2O is always liquid)
(g) - denotes a gas
(aq)- Denotes an aqeuos or a dissolved
mixture.
Applying these symbols to the previous
equation:
4H (g) + O2 (g)
2H2O (l)
2. Ionic
equations
Below is the equation of the reaction of
silver nitrate and sodium chloride:
AgNO3 (aq) + NaCl (aq)
AgCl (s) + NaNO3 (aq)
The equation of the reaction of Silver
Nitrate and Sodium Chloride can be
converted to an ionic equation by:
AgNO3 (aq) + NaCl (aq)
AgCl (s) + NaNO3 (aq)
The equation of the reaction of Silver Nitrate and
Sodium Chloride can be converted to an ionic
equation by:
1. Expand the equation to show the
individual ions present:
Ag (aq) NO3 (aq) + Na (aq) Cl (aq)
Ag Cl (s) + Na (aq) NO3 (aq)
2. Cancel out any ions which have not changed
state from one side of the equation to the other. the
Na and the NO3 ions. These ions are called
spectator ions.
Ag (aq) NO3 (aq) + Na (aq) Cl (aq)
Ag Cl (s) + Na (aq) NO3 (aq)
3. Rewrite the equation.
Ag (aq)
+ Cl (aq)
Ag Cl (s)
4. Balance the number of similar ions and the
electrical charges on both sides of the equation.
Ag (aq)
+ Cl (aq)
Ag Cl (s)
The numbers of
ions and charges
are already
balanced on this
Knowing how to assign the state of en element:
To assign the state of an element you should know
what state that compound normaly exists as at room
temperature and pressure.
KI (aq)
+
Pb NO3 (aq)
KNO3
(?) +
PbI (?)
E.g The reaction of Potassium Iodide and Lead
Nitrate gives Potassium Nitrate and Lead iodide.
KI (aq)
+
Pb NO3 (aq)
KNO3 (aq) +
PbI (s)
Potassium nitrate is soluble so it will exist as aqueous
ions. The lead iodide is not soluble so it will be solid
and produce a precipitate.
Practice questions:
Balance and assign state symbols to the following
equations:
1. CuO + HNO3
Cu(NO3)2 + H2O
2. Al + Cl2
AlCl3
3. Na + H2O
NaOH + H2
4. K2CO3 + H2SO4
5. Fe + H2SO4
K2SO4 + H2O + CO2
FeSO4 + H2
6. Pb(NO3)2 + NaCl
PbCl2 + NaNO3
Give the Balanced Ionic equations of the following, assigning state symbols to the following:
1. NaOH + HCl
NaCl
2. Mg(OH)2 (s) + 2HNO3(aq)
+
H2O
Mg(NO3)2 + 2H2O
Rules To writing Ionic Equations:
Represent elements by their symbols. Solid elements, use the symbol of the
single atom, e.g Fe(s), Ag(s), Cl(s). Gases use the symbol of the Molecule,
example the diatomic gases ydrogen, oxgyen and Nitrogen would be
written: H2(g), O2(g) , N2(g) ,etc.
Balance the Equation by placing whole number co-efficients at the front of
each term of the equation where warranted. Do not change the numbers withi
the formula.
e.g the reaction of Nitrogen and Hydrogen gas to give Ammonium NH4(g):
N2 (g) + H8 (g)
2NH4
Balancing by writing the molecular formula
of Hydrogen gas as H8 is not correct.
N2 (g) + 4H2 (g)
2NH4
Rules To writing Ionic Equations:
3. Remember that Ionic substances break up to produce
ions as part of a solution, covalently bonded substances,
covalently bonded atoms do not break up and metals exist
as seperate atoms.
4. it is permissible to change the whole number co-efficient
of bracketed groups which are part of a compound such as
Pb(NO3),as this does not change the formula of the group.
Rules To writing Ionic Equations:
Compounds written as Whole molecules and not individual ions oare:
1. Solids or non-soluble precipitates which result from mixing previously aqueous
ions are written with their molecular formula and not as seperate ions e.g
Ag+(aq) + NO3 2- (aq) + Cl- (aq)
AgCl(s) + H+ (aq) + NO3 2-(aq)
Would be written as the un ionised
molecular form.
2. Non-electrolytes such as glucose.
Electrolytes are substances which are capable of disassociating to give free
ions when dissolved and produce solutions which are able to conduct electricity,
this is why they are called electrolytes.
3. Weak electrolytes such as ethanoic acid, NH3,( ammonia) water and solids
It follows from this that water is written as H2O, However OH- ions and H+
ions which lead to the production of water are written as seperate ions.
E.g Mg2+ (aq) + 2OH-(aq) + H+ (aq)
2 OH- (aq) + H+(aq)
+
Cl- (aq)
H2O(l)
Mg2+ (aq)+ 2Cl- (aq) +H2O (l)