Useful resource for Junior Cert Science- Chemistry

1. 29/05/13
Junior CycleScienceJunior CycleScience
Chemistry in ActionChemistry in Action
Edited and Reproduced by
Theresa Lowry-Lehnen
RGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling, Dip Adv Psychotherapy, BSc
(Hon’s) Clinical Science, PGCE (QTS) , H. Dip. Ed, MEd, Emotional Intelligence (Level 9) MHS Accredited

2. 29/05/13
Balancing equationsBalancing equations
Consider the following reaction:
Na O
H H
H H
Na
O
H
+ +
This equation doesn’t balance – there are 2 hydrogen
atoms on the left hand side (the “reactants” and 3 on
the right hand side (the “products”)
Sodium + water sodium hydroxide + hydrogen
Na + H2O NaOH + H2

3. 29/05/13
Balancing equationsBalancing equations
We need to balance the equation:
Na
O
H H
H H
Na
O
H
Sodium + water sodium hydroxide + hydrogen
+ +
Na
O
H H
Na
O
H
Now the equation is balanced, and we can write it as:
2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

4. 29/05/13
Some examplesSome examples
Mg + O2
Zn + HCl
Fe + Cl2
NaOH + HCl
CH4 + O2
Ca + H2O
NaOH + H2SO4
CH3OH + O2
MgO
ZnCl2 + H2
FeCl3
NaCl + H2O
CO2 + H2O
Ca(OH)2 + H2
Na2SO4 + H2O
CO2 + H2O
2
2
2 3
2
2
2
2 3
2
2
2
2
2 4

5. 29/05/13
Testing for carbon dioxideTesting for carbon dioxide
Gas
Limewater turns
milky/cloudy
Limewater

6. 29/05/13
Adding acid to carbonatesAdding acid to carbonates
Carbonates are compounds containing carbon and oxygen. When an acid is
added to a carbonate the carbonate starts to fizz. A gas called
_________ _______ is produced.
Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water
CaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)2

7. 29/05/13
Flame testsFlame tests
CompoundCompound Colour of flameColour of flame

8. 29/05/13
Flame testsFlame tests
Compounds containing lithium, sodium, potassium, calcium and
barium can be recognised by burning the compound and
observing the colours produced:
Lithium
Red
Sodium
Yellow
Potassium
Lilac
Calcium
Brick red
Barium
Green

9. 29/05/13
Metal ionsMetal ions
Metal compounds in a solution contain metal ions. For example,
consider calcium chloride:
Chlorine is in
group 7 so a
chloride ion
will be Cl-
Calcium is in
group 2 and has
two electrons in
its outer shell, so
it will form a Ca2+
ion.
Calcium chloride has the formula CaCl2

10. 29/05/13
Metal ions and precipitatesMetal ions and precipitates
Some metal ions form precipitates, i.e. an insoluble solid that
is formed when sodium hydroxide is added to them. Consider
calcium chloride:
Ca2+
(aq) + OH-
Ca(OH)2 (s)2

11. 29/05/13
Metal ions and precipitatesMetal ions and precipitates
Some metal ions form precipitates, i.e. an insoluble solid that
is formed when sodium hydroxide is added to them. Consider
calcium chloride:
Ca2+
(aq) + OH-
Ca(OH)2 (s)2
Metal ionMetal ion Precipitate formedPrecipitate formed ColourColour
Calcium Ca2+ Calcium hydroxide: Ca2+
(aq) + OH-
(aq) Ca(OH)2 (s) White
Aluminium Al3+
Magnesium Mg2+
Copper(II) Cu2+
Iron(II) Fe2+
Iron(III) Fe3+

12. 29/05/13
Testing for chloride and sulphate ionsTesting for chloride and sulphate ions
Test 1: Chloride ions
Add a few drops of dilute nitric acid to the chloride ion
solution followed by a few drops of silver nitrate.
Test 2: Sulphate ions
Add a few drops of dilute hydrochloric acid to the sulphate
ion solution followed by a few drops of barium chloride.
Precipitate formed = silver chloride (white)
Precipitate formed = barium sulphate (white again)
For each test state: 1) The colour of the precipitate
2) What compound it is

13. 29/05/13
Ammonium, nitrate, bromide and iodide ionsAmmonium, nitrate, bromide and iodide ions
Ammonium ions:
Add sodium hydroxide and test the gas using damp litmus
paper – ammonia gas turns damp litmus paper blue.
Nitrate ions:
Add sodium hydroxide followed by aluminium powder and test
using damp litmus paper.
Bromide and iodide ions:
Add a few drops of dilute nitric acid followed by a few drops
of silver nitrate solution. A pale yellow precipitate should be
formed for bromide ions and a darker yellow precipitate for
iodide ions.

14. 29/05/13
Thermal decompositionThermal decomposition
A “thermal decomposition” reaction occurs when a compound
breaks down (“decomposition”) through the action of heat.
Practical work:
Perform a thermal decomposition reaction
on each of these compounds and state:
1) The colour changes you observed
2) The reaction that happened
Copper carbonate:
Zinc carbonate:
CuCO3 (s) CuO(s) + CO2 (g) (Green – Black)
ZnCO3 (s) ZnO(s) + CO2 (g) (White – Yellow)

15. 29/05/13
Sulphuric acidSulphuric acid
Sulphuric acid has many important uses – car batteries, detergents,
fertilisers etc.
How sulphuric acid is made:
Step 1: Burn sulphur in air:
Step 2: Pass the sulphur dioxide over a vanadium oxide catalyst at 450OC:
Step 3: Dissolve the sulphur trioxide in sulphuric acid:
Step 4: Add water to the oleum:
Sulphur + oxygen sulphur dioxide
Sulphur trioxide + conc. sulphuric acid oleum
Sulphur dioxide + oxygen sulphur trioxide
Oleum + water sulphuric acid

16. 29/05/13
Reversible ReactionsReversible Reactions
When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants
are added or taken away) an EQUILIBRIUM is achieved – in other words,
the reaction goes at the same rate in both directions:
A + B C + D
Endothermic reactions
Increased temperature:
Decreased temperature:
A + B C + D
A + B C + D
More products
Less products
Exothermic reactions
Increased temperature:
Decreased temperature:
A + B C + D
Less products
More products
A + B C + D

17. 29/05/13
Sulphuric acidSulphuric acid
Step 2 in the manufacture of sulphuric acid is an example of a
reversible reaction:
2SO2 + O2 2SO3
ExothermicEndothermic
What would happen if the temperature was decreased?
Solution – use 450O
C as a compromise
The reaction would favour the production of sulphur trioxide
BUT the reaction would happen at a slower rate.

18. 29/05/13
Iron and SteelIron and Steel
In previous work we considered the role of the
blast furnace in extracting iron from its ore.
The iron contains roughly 5% carbon and
different metals and is very ________. In
order to reduce these impurities and convert
the iron into _________ the molten iron is
transferred into another furnace where it is
mixed with recycled scrap iron and pure
___________. The oxygen reacts with the
metal impurities to form ________ oxides.
Calcium carbonate is also added to remove
some of the acidic oxides as _______ when
the furnace is tilted.
Words – slag, brittle, steel, oxygen, acidic

19. 29/05/13
Making steel – the reactionsMaking steel – the reactions
1) Mixing oxygen with silicon impurities:
2) Decomposition of limestone:
3) Adding these products together:
Silicon + oxygen Silicon oxide
Calcium carbonate calcium oxide + carbon dioxide
Silicon oxide + calcium oxide calcium silicate
Steel with a high
carbon content is
strong but brittle
Steel with a low
carbon content is
easily shaped
Steel with chromium
and nickel is called
stainless steel

20. 29/05/13
TitaniumTitanium
Titanium is a strong metal used in planes, replacement hip
joints, bikes etc. Two steps are used in its manufacture:
Step 1: Convert titanium dioxide (ore) to titanium chloride
Step 2: Displace the titanium using sodium or magnesium:
Titanium chloride + sodium titanium + sodium chloride
In this reaction the
titanium is displaced my a
more reactive metal. This
reaction is done in an argon
atmosphere to avoid any
further reactions.
Titanium ions have a
charge of 4+ and gain four
electrons to become
titanium atoms. This is a
reduction reaction.

21. 29/05/13
AluminiumAluminium
Aluminium is a fairly reactive metal that doesn’t
corrode due to forming a thin layer of
aluminium oxide. This explains why greenhouses
don’t rust and don’t need to be painted.
A thicker layer of aluminium oxide can be made artificially.
There are two stages:
1) Remove the natural layer
by placing the aluminium in
sodium hydroxide.
2) Use electrolysis on
sulphuric acid with the
aluminium as the positive
electrode. This is called
anodising.
+
+
+
+
-
-
-
-
H2SO4
Al

22. 29/05/13
ElectroplatingElectroplating
+
+
+
+
-
-
-
-
Solution containing
silver ions
Silver
electrode
Object to
be plated