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Ionic Equations and State Symbols. There are 2 types of equations:. 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.

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Presentation Transcript
slide1

Ionic Equations

and

State Symbols

slide2

There are 2 types of equations:

  • 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 + O2 2HO

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.

slide3

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.

slide4

Notice, the chemical formula of the compound has not changed. Water is still H2O and Oxygen is still O2.

slide5

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)

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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:

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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)

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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 equation.

slide9

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.

slide10

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 K2SO4 + H2O + CO2

5. Fe + H2SO4 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 + H2O

2. Mg(OH)2 (s) + 2HNO3(aq) Mg(NO3)2 + 2H2O

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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

N2 (g) + 4H2 (g) 2NH4

Balancing by writing the molecular formula of Hydrogen gas as H8 is not correct.

slide12

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.

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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)

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) + Cl- (aq) Mg2+ (aq)+ 2Cl- (aq) +H2O (l)

2 OH- (aq) + H+(aq) H2O(l)

Would be written as the un ionised molecular form.