science form 4- chapter ff5
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SCIENCE FORM 4
CHAPTER 5:ENERGY AND
CHEMICALCHANGES
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5.1 PHYSICAL AND CHEMICAL CHANGES
- Examples involving physical changes:(a) Melting of ice
(b) Evaporation of water
(c) Dissolving sugar in water(d) Crystallisation of sodium chloride
from its saturated solution
(e) Heating of iodine crystals
(f) Heating of wax
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5.1 PHYSICAL AND CHEMICAL CHANGES
Melting of ice Evaporation of water
http://www.google.com.my/url?sa=i&rct=j&q=evaporation++sea+water&source=images&cd=&cad=rja&docid=3ge595uLd_yKhM&tbnid=Z8FSNyQtr3G_qM:&ved=0CAUQjRw&url=http://ga.water.usgs.gov/edu/watercycleevaporation.html&ei=VMSYUZrCNM6trAeG3ICIBA&bvm=bv.46751780,d.bmk&psig=AFQjCNGMjpZtL2Y24coz1qmcq5WSh-1xfw&ust=1369052625762793http://www.google.com.my/url?sa=i&rct=j&q=melting+of+ice&source=images&cd=&cad=rja&docid=64GdR4m9ftaArM&tbnid=zRwGJUH8H1OUlM:&ved=0CAUQjRw&url=http://blogs.yis.ac.jp/19miyoshiay/2012/09/25/science-a-little-bit-of-matter/&ei=W76YUci0L4rIrQf5jYGYAg&bvm=bv.46751780,d.bmk&psig=AFQjCNEIMEToM6e_90RKap1UxiQ0zEbvhw&ust=1369051074421864 -
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5.1 PHYSICAL AND CHEMICAL CHANGES
Dissolving of sugar in water Heating iodine crystals
http://www.google.com.my/url?sa=i&rct=j&q=heating+iodine+crystals&source=images&cd=&cad=rja&docid=hwossyD3T0PFDM&tbnid=L8sBAyygOLI72M:&ved=0CAUQjRw&url=http://math.ucr.edu/home/baez/networks/networks_18.html&ei=GcSYUfH9AcWzrAeVyICoAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHficlrvZBxMwnVeO8g1MQexSKvnQ&ust=1369052484165440http://www.google.com.my/url?sa=i&rct=j&q=dissolving+sugar+in+water&source=images&cd=&cad=rja&docid=2W-fhSf_xh-mCM&tbnid=uU6NHpLKFWOy-M:&ved=0CAUQjRw&url=http://www.whycenter.com/why-does-sugar-dissolve-in-water/&ei=PMOYUYWWBIWFrgfLuYDIDQ&bvm=bv.46751780,d.bmk&psig=AFQjCNH6T7sNbUgz6qKyZRJRYLhhfdxxOw&ust=1369052304601326 -
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5.1 PHYSICAL AND CHEMICAL CHANGES
(ii) Chemical change
- Produces new substances that have
properties different from those of the
original substance.- Usually irreversible.
- Examples involving chemical changes:
(a) Burning of a paper(b) Colour of a peeled apple changes
when it is exposed to air
(c) Frying an egg
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5.1 PHYSICAL AND CHEMICAL CHANGES
(d) Combustion of fuel(e) When iron filings are heated with sulphur
powder, the mixture glows brightly. A
black solid, iron sulphide is formed.Iron + Sulphur Iron sulphide
(f) When magnesium ribbon is heated,
it burns with a bright flame. A white solid,
magnesium oxide is formed.
Magnesium + Oxygen Magnesium
oxide
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5.1 PHYSICAL AND CHEMICAL CHANGES
(g) Zinc reacts with blue copper sulphatesolution to form a colourless zinc
sulphate solution and brown copper.
Zinc + Copper sulphate Zinc sulphate+ Copper
(h) Iron nail rust when water and oxygen are
present. Rust is brown.
Iron + Oxygen + Water Rust
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5.1 PHYSICAL AND CHEMICAL CHANGES
(i) Heating green copper carbonateproduces black copper oxide and
releases carbon dioxide.
Copper carbonate Copper oxide +Carbon dioxide
(j) Mixing potassium iodide and lead nitrate
solution forms lead iodide, a yellow
precipitate.
Potassium + Lead Potassium + Lead
iodide nitrate nitrate iodide
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5.1 PHYSICAL AND CHEMICAL CHANGES
Frying an egg Browning of an apple
http://www.google.com.my/url?sa=i&rct=j&q=brown+oxidation+apple+&source=images&cd=&cad=rja&docid=E40GigtdemxlNM&tbnid=Mtnw0O4PokePQM:&ved=0CAUQjRw&url=http://ursulaethomasardysshealthandwellness.blogspot.com/2010_04_01_archive.html&ei=ugeZUaegNcqJrAfuxIDYDQ&bvm=bv.46751780,d.bmk&psig=AFQjCNEJ7OHO7SpAZACWou4gUPk4gI4UPw&ust=1369069673108365http://www.google.com.my/url?sa=i&rct=j&q=frying+an+egg&source=images&cd=&cad=rja&docid=y3yAiUJvartiIM&tbnid=RGu_fTwuvHF6SM:&ved=0CAUQjRw&url=http://whatscookingamerica.net/Eggs/FriedEgg.htm&ei=pv6YUdbjFMTqrAfxyYDwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNElgBK3nisqBoDeu4JJa7WI-CiRVQ&ust=1369067466410515 -
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5.1 PHYSICAL AND CHEMICAL CHANGES
Heating a mixture of iron filings andsulphur powder
Reaction of zinc with coppersulphate solution
http://www.google.com.my/url?sa=i&rct=j&q=zinc+reacting+with+copper+sulfate+solution&source=images&cd=&cad=rja&docid=deDwTD5bQUL7tM&tbnid=fUTUI31WX9WK5M:&ved=0CAUQjRw&url=http://www.visualphotos.com/image/1x6037953/zinc_displacing_copper_in_copper_sulphate_solution&ei=UQSZUfXrMZDorQekn4H4Bw&bvm=bv.46751780,d.bmk&psig=AFQjCNGxQAMqtkdKoW1IP5RTQrwRMBW4Hw&ust=1369068771256525http://www.google.com.my/url?sa=i&rct=j&q=iron+heated+sulfur&source=images&cd=&cad=rja&docid=fxzMKf7_72ajrM&tbnid=HR3ZFcC2gYSEOM:&ved=0CAUQjRw&url=http://www.youtube.com/all_comments?threaded=1&v=q-pWpBcWNek&ei=NQOZUezNMc2GrgfH74HYBw&bvm=bv.46751780,d.bmk&psig=AFQjCNGhEHwTUnkNw6KsNuqpqAG4VzJxQg&ust=1369068667897912 -
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5.1 PHYSICAL AND CHEMICAL CHANGES
Aspect Physical changes Chemical changes
Formation of new substance No Yes
Reversibility Reversible Difficult to reverse
Energy needed Less energy needed More energy needed
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
There are two types of chemical reactions:(i) Exothermic reactions
- Reactions which release heat to the
surroundings are called exothermicreactions.
- Temperature of the surroundings
increases.
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
(ii) Endothermic reactions
- Reactions which absorb heat from
the surroundings.
- Temperature of the surroundings
decreases.
During chemical reactions, old bonds in
the reactants are broken and new
bonds in the products are formed.
The breaking down of old bonds absorbs
heat energy whereas the formation of
new bonds releases heat energy.
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
Breaking an old bond absorbs heat energy Forming a new bond releases heat energy
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
In exothermic reactions, the heat energy
absorbed to break the old bonds in the
reactants is less than the heat energy
released when new bonds are formed in
the products. There is a net of heat
energy loss.
The temperature of the surroundings
increases due to the heat energy that isreleased.
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
In endothermic reactions, the heat energyabsorbed to break the old bonds in the
reactants is greater than the heat energy
released when the new bonds are formed
in the products. There is a net of heat
energy gain.
The temperature of the surroundings
decreases due to heat energy is absorbed
from the surroundings.
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
In exothermic reactions, the heat energy absorbed to break the old bonds in the
reactants is less than the heat energy released when the new bonds are formed in theproducts
http://www.google.com.my/url?sa=i&rct=j&q=exothermic+reaction+animation&source=images&cd=&cad=rja&docid=jNawKRtgXAN6nM&tbnid=oB5MMP9f0pnA6M:&ved=0CAUQjRw&url=http://www.rpdp.net/sciencetips_v2/P12A6.htm&ei=HmCaUZ2aIYHUrQfgi4GgAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFF5hcPMshOftc4qcvnQ4BlmWnZ8A&ust=1369157534867967 -
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
In endothermic reactions, the heat energy absorbed to break the old bonds in the
reactants is greater than the heat energy released when the new bonds are formed inthe products
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
Haber process is used to manufacture
ammoniain the industry. Ammonia is an
important material for making nitrogenous
fertilisers.
In the Haber process, nitrogen and
hydrogen gases are mixed together. The
mixture is passed over an iron catalyst.
Iron catalystNitrogen + Hydrogen Ammonia
450 C
200 atm
http://www.google.com.my/url?sa=i&rct=j&q=reversible+arrow+chemistry&source=images&cd=&cad=rja&docid=OalOMglJ5gOZ0M&tbnid=MyASuVTozRu5aM:&ved=0CAUQjRw&url=http://www.citycollegiate.com/chemical_equilibrium5.htm&ei=dGqaUfmrMcrorQeJ7oCwDw&bvm=bv.46751780,d.bmk&psig=AFQjCNEmU5_wAzU7ulJ0Z_ZvUOwdv7K9_A&ust=1369160671391484 -
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
Iron catalyst
Reactor
Coolant out
Coolant in
Condenser
Leftover H2+ N2
Liquid ammonia
H2+ N2
Haber process
http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjRw&url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/chemical/batchcontinuousrev1.shtml&ei=_3maUbnAF4ONrQe964HQAQ&bvm=bv.46751780,d.bmk&psig=AFQjCNFXFpREM9bWgDyJ_C15_Y3hkSwoGQ&ust=1369164608654638http://www.google.com.my/url?sa=i&rct=j&q=haber+process&source=images&cd=&docid=duDK45jXlHSxoM&tbnid=fShQDJ-zveMOdM:&ved=0CAUQjR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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
Contact process is used to manufacture
sulphuric acid in the industry.
Step 1: Sulphur is burnt in air to produce
sulphur dioxide.Sulphur + Oxygen Sulphur
dioxide
Step 2: A mixture of sulphur dioxide andair are passed over vanadium(V)
oxide catalyst at 450 C to produce
sulphur trioxide.
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
Step 3: Sulphur trioxide is dissolved inconcentrated sulphuric acid to
produce oleum.
Sulphur + Concentrated Oleum
trioxide sulphuric acid
Vanadium(V)
oxide catalystSulphur dioxide + Oxygen Sulphur trioxide
450 C
http://www.google.com.my/url?sa=i&rct=j&q=reversible+arrow+chemistry&source=images&cd=&cad=rja&docid=OalOMglJ5gOZ0M&tbnid=MyASuVTozRu5aM:&ved=0CAUQjRw&url=http://www.citycollegiate.com/chemical_equilibrium5.htm&ei=dGqaUfmrMcrorQeJ7oCwDw&bvm=bv.46751780,d.bmk&psig=AFQjCNEmU5_wAzU7ulJ0Z_ZvUOwdv7K9_A&ust=1369160671391484 -
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5.2 HEAT CHANGE IN CHEMICAL REACTIONS
Step 4: The oleum is diluted with water to
produce concentrated sulphuric
acid.
Oleum + Water Concentratedsulphuric acid
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5.3 THE REACTIVITY SERIES OF METALS
Why do gold, silver and platinum exist
as elements in the Earths crust and
whereas metals such as sodium and
potassium do not exist as elements in
the Earths crust?
Some metals are more reactive than
others. Different metals show different
reactivity with water, acids and oxygen.
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5.3 THE REACTIVITY SERIES OF METALS
The reactions involving metals:
(i) Reaction of reactive metal with water to
produce alkali and hydrogen.
Metal + Water Alkali + Hydrogen(ii) Reaction of reactive metal with dilute
acid to produce a salt and hydrogen.
Metal + Dilute acid Salt + Hydrogen(iii) Reaction of metal with oxygen to form
metal oxide
Metal + Oxygen Metal oxide
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5.3 THE REACTIVITY SERIES OF METALS
Based on their reactivity with oxygen,
metals and carbon (non-metal) can be
arranged in a reactivity series as follows:Potassium
Sodium
CalciumMagnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Copper
Silver
Gold
Potato
Soup
CanMake
All
Cruel
Zoos
In
The
Land
Change
So
Good
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5.3 THE REACTIVITY SERIES OF METALS
The position of carbon in the reactivity seriesis determined by comparing its attraction for
oxygen with other metals.
When carbon is heated with a metal oxide,carbon can remove oxygen from the metal
oxide if carbon is more reactive than the
metal.
When zinc oxide and iron oxide are heated
with carbon, the oxygen in the metal oxides
are removed by carbon. Therefore, carbon
is more reactive than zinc and iron.
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5.3 THE REACTIVITY SERIES OF METALS
When carbon is heated with aluminium
oxide, the carbon cannot remove oxygen
from aluminium oxide.
This means that carbon is more reactive
than zinc and iron but less reactive than
aluminium. Therefore, carbon is positioned
between aluminium and zinc in the
reactivity series.
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5.4 APPLICATION OF REACTIVITY SERIES OF METALS
Most metals in the Earths crust are
reactive. They react readily with other
elements to form compoundssuch as
oxides, sulphides and carbonates. These
compounds are called ores.
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5.4 APPLICATION OF REACTIVITY SERIES OF METALS
Ore Composition
Bauxite Aluminium oxide
Cassiterite Tin(IV) oxide
Haematite Iron(III) oxide
Sphaletite Zinc sulphide
Sedimentary rock Calcium carbonate
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5.4 APPLICATION OF REACTIVITY SERIES OF METALS
The method of extracting a metal from its
ore depends on its position in the
reactivity series.
Metals below carbon in the reactivity
series can be extracted from their oxides
with using carbon because they are less
reactive than carbon.
Carbon is used for extraction because it is
cheap and readily available.
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5.4 APPLICATION OF REACTIVITY SERIES OF METALS
Metals above carbon in the reactivityseries cannot be extracted using carbon
because they are more reactive than
carbon. They are extracted using
electrolysis.
Tin ore or cassiterite is tin(IV) oxide. Tin
is extracted by heating cassiterite with
carbon (coke) and limestone at hightemperature in a blast furnace.
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5.4 APPLICATION OF REACTIVITY SERIES OF METALS
Carbon removes the oxygen from tin(IV)oxide because it ismore reactive than tin.
Tin(IV) oxide + Carbon Tin + Carbon
dioxide Limestone is added to react with the
impurities in the tin ore. Slag is formed.
Two products are collected at the bottom ofthe blast furnace. Molten slag floats on the
molten tin. This allow the two products to
flow separately.
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5.4 APPLICATION OF REACTIVITY SERIES OF METALS
Extraction of tin in a blast furnace
Molten iron
Blast furnace
Tin(IV) oxide, coke and
limestone
Slag
Blast of hot air
http://images.yourdictionary.com/blast-furnacehttp://images.yourdictionary.com/blast-furnacehttp://images.yourdictionary.com/blast-furnacehttp://images.yourdictionary.com/blast-furnacehttp://images.yourdictionary.com/blast-furnacehttp://images.yourdictionary.com/blast-furnacehttp://images.yourdictionary.com/blast-furnace -
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5.5 ELECTROLYSIS
Electrolysis is the decomposition of an
electrolyte by electricity. An electrolyte is a liquid or solution which
contains free-moving ions that can
conduct electricity.
The electrodes are conductors whichcarry
electricity into or out of an electrolyte.
The electrode joined to the positiveterminal of the dry cell is called the anode
whereas the electrode joined to the
negative terminal is called the cathode.
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5.5 ELECTROLYSIS
During electrolysis, the positively-
charged ions (cations) are attracted to
the cathode and receive electrons. The
negatively-charged ions (anions) are
attracted to the anode and releaseelectrons.
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5.5 ELECTROLYSIS
Bromine
gas Lead
metal
Molten lead
bromide
Electrolysis
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5.5 ELECTROLYSIS
Uses of electrolysis in industry:
(i) Electroplating
- To prevent iron objects from corrosion,
they are electroplated with a thin layerof unreactive metals such as
copper, silver and chromium.
- Electroplating make these objectsresistant to corrosion and more
attractive.
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5.5 ELECTROLYSIS
Electroplating an iron spoon with copper
Copper
asanode
Iron
spoonas
cathode
Copper sulphate
solution
Copper ions
Rules for electroplating:
(i) Anode : Plating metal
(ii) Cathode: Object to be
electroplated(i) Electrolyte: Solution of the
plating metal
Rheostat
http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417http://www.google.com.my/url?sa=i&rct=j&q=rheostat+symbol&source=images&cd=&cad=rja&docid=jF0Gb6tR8aHRwM&tbnid=BWIF3bVfk-YnBM:&ved=0CAUQjRw&url=http://symbologic.info/elec_symbols.htm&ei=fIacUf66OoXuiAfB0IDwCg&bvm=bv.46751780,d.aGc&psig=AFQjCNFyl7OALU1zPWfc87SuF77Z0KxYow&ust=1369298184014919http://www.google.com.my/url?sa=i&rct=j&q=electroplating+iron+spoon+with+copper&source=images&cd=&cad=rja&docid=2AtEzCPrCr-0kM&tbnid=kg8fiTogP4yJKM:&ved=0CAUQjRw&url=http://moodle.rockyview.ab.ca/mod/book/print.php?id=118120&chapterid=91369&ei=A3GcUYWsHo-3rAef1YDIBQ&bvm=bv.46751780,d.bmk&psig=AFQjCNHSh945z56_G_BPUO7O2HO-wnKNFQ&ust=1369293258620417 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5.5 ELECTROLYSIS
- At the anode, the copper dissolves toform positively-charged copper ions.
- At the cathode, the copper ions receive
electrons to form a coat of copper onthe iron spoon.
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5.5 ELECTROLYSIS
- A rheostat is used to control the currentflow in the circuit so that a small
current is used and the object to be
electroplated must be cleaned with asandpaper before electrolysis. These
steps are to obtain good results.
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5.5 ELECTROLYSIS
Iron spoon electroplated with copper
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5.5 ELECTROLYSIS
(ii) Extraction of reactive metals
- Metals which are more reactive than
carbon are extracted from their ores by
electrolysis.
- For example, aluminium can be
extracted from its ore,bauxite
(aluminium oxide).- Bauxite is first purified and then dissolved
in cryolite. This is to lower the melting
point of aluminium oxide.
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5.5 ELECTROLYSIS
- When aluminium oxide melts, aluminium
ions and oxide ions are free to move.
- When electricity is passed through the
electrolyte, the positively-chargedaluminium ions are attracted to the
cathode. They receive electrons and
become aluminium atoms.- The molten aluminium formed is
channelled into moulds.
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5.5 ELECTROLYSIS
- At the anode, the oxide ions lose
electrons to become oxygen atoms.
The oxygen atoms combine together to
form oxygen gas.
Aluminium is extracted from bauxite by electrolysis
http://www.google.com.my/url?sa=i&rct=j&q=bauxite+electrolysis&source=images&cd=&cad=rja&docid=8LeoAnYaoXyO0M&tbnid=cboLFdvntFIUGM:&ved=0CAUQjRw&url=http://www.ibchem.com/IB/ibnotes/full/ope_htm/hall_cell.htm&ei=a4GcUfOjCsSziQfF5oDQAg&bvm=bv.46751780,d.aGc&psig=AFQjCNEQ6k7XjDvCyDOIyWKcd7-L7LUY3A&ust=1369297640821399 -
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5.6 THE PRODUCTION OF ELECTRICAL ENERGY
FROM CHEMICAL REACTIONS
A simple cell consists of two electrodesand an electrolyte.
The more reactive metal is the negative
terminal which releases electronswhereas the less reactive metal acts as a
positive terminal which receives
electrons.
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5.6 THE PRODUCTION OF ELECTRICAL ENERGY
FROM CHEMICAL REACTIONS
A simple cell
Copper
sulphate
solution
Magnesium
Copper
http://www.google.com.my/url?sa=i&rct=j&q=voltaic+cell+&source=images&cd=&cad=rja&docid=qKWWsjTgtoC9dM&tbnid=TTQRS3bNsGSb1M:&ved=0CAUQjRw&url=http://chem2u.blogspot.com/2011/08/simple-voltaic-cell.html&ei=d_ScUdyAO4eBrgfRj4DwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNEtbKRrSqEovYNd44CL4XBWYYTsiw&ust=1369326664256544http://www.google.com.my/url?sa=i&rct=j&q=voltaic+cell+&source=images&cd=&cad=rja&docid=qKWWsjTgtoC9dM&tbnid=TTQRS3bNsGSb1M:&ved=0CAUQjRw&url=http://chem2u.blogspot.com/2011/08/simple-voltaic-cell.html&ei=d_ScUdyAO4eBrgfRj4DwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNEtbKRrSqEovYNd44CL4XBWYYTsiw&ust=1369326664256544http://www.google.com.my/url?sa=i&rct=j&q=voltaic+cell+&source=images&cd=&cad=rja&docid=qKWWsjTgtoC9dM&tbnid=TTQRS3bNsGSb1M:&ved=0CAUQjRw&url=http://chem2u.blogspot.com/2011/08/simple-voltaic-cell.html&ei=d_ScUdyAO4eBrgfRj4DwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNEtbKRrSqEovYNd44CL4XBWYYTsiw&ust=1369326664256544http://www.google.com.my/url?sa=i&rct=j&q=voltaic+cell+&source=images&cd=&cad=rja&docid=qKWWsjTgtoC9dM&tbnid=TTQRS3bNsGSb1M:&ved=0CAUQjRw&url=http://chem2u.blogspot.com/2011/08/simple-voltaic-cell.html&ei=d_ScUdyAO4eBrgfRj4DwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNEtbKRrSqEovYNd44CL4XBWYYTsiw&ust=1369326664256544http://www.google.com.my/url?sa=i&rct=j&q=voltaic+cell+&source=images&cd=&cad=rja&docid=qKWWsjTgtoC9dM&tbnid=TTQRS3bNsGSb1M:&ved=0CAUQjRw&url=http://chem2u.blogspot.com/2011/08/simple-voltaic-cell.html&ei=d_ScUdyAO4eBrgfRj4DwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNEtbKRrSqEovYNd44CL4XBWYYTsiw&ust=1369326664256544http://www.google.com.my/url?sa=i&rct=j&q=voltaic+cell+&source=images&cd=&cad=rja&docid=qKWWsjTgtoC9dM&tbnid=TTQRS3bNsGSb1M:&ved=0CAUQjRw&url=http://chem2u.blogspot.com/2011/08/simple-voltaic-cell.html&ei=d_ScUdyAO4eBrgfRj4DwCg&bvm=bv.46751780,d.bmk&psig=AFQjCNEtbKRrSqEovYNd44CL4XBWYYTsiw&ust=1369326664256544 -
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5.6 THE PRODUCTION OF ELECTRICAL ENERGY
FROM CHEMICAL REACTIONS
Refer to the diagram above: Magnesium and copper strips are used as
electrodes with copper sulphate solution
as the electrolyte. Magnesium (negative terminal) is more
reactive than copper (positive terminal).
Therefore, magnesium atoms releaseelectrons to form magnesium ions which
move into the electrolyte. As a result,
the magnesium strip becomes thinner.
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5.6 THE PRODUCTION OF ELECTRICAL ENERGY
FROM CHEMICAL REACTIONS
The electrons flow to the copper stripthrough the wire and this produces
electricity.
Positively-charged copper ions from theelectrolyte receive the electronsand
form copper atoms. This causes copper to
be deposited on the copper strip.
Therefore, the copper strip becomes
thicker.At the same time, the blue colour
of the copper sulphate solution fades.
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5.6 THE PRODUCTION OF ELECTRICAL ENERGY
FROM CHEMICAL REACTIONS
Type of cell Uses Advantages Disadvantages
Dry cells Used in portable
devices such as
radios, cassette
players, cameras
and toys
Light
Small
Portable
Cheap
Non-rechargeable
Not long-lasting
Leakage may happen
when the zinc case
becomes thinner
Lead-acid
accumulators
Used in vehicles High voltage
Rechargeable
Long-lasting if
well taken
care of
Heavy
Expensive
Acid might spill
Distilled water needs
to be added
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5.6 THE PRODUCTION OF ELECTRICAL ENERGY
FROM CHEMICAL REACTIONS
Type of cell Uses Advantages Disadvantages
Nickel-
cadmium
batteries
Used in electronic
devices such as
digital cameras
Rechargeable
Long-lasting
Expensive
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5.7 CHEMICAL REACTIONS THAT OCCUR IN THE
PRESENCE OF LIGHT
During photosynthesis, chlorophyll absorbslight energy to split water molecules into
hydrogen and oxygen.
The oxygen is released into the atmospherewhereas the hydrogen atoms react with
carbon dioxide to form glucose.
Carbon + Water Light Glucose + Oxygendioxide Chlorophyll
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5.7 CHEMICAL REACTIONS THAT OCCUR IN THE
PRESENCE OF LIGHT
Photosynthesis requires light
5 8 INNOVATIVE EFFORTS IN THE DESIGN OF
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5.8 INNOVATIVE EFFORTS IN THE DESIGN OF
EQUIPMENT USING CHEMICAL REACTIONS AS
SOURCES OF ENERGY
We should use electric cells efficientlytoprevent wastage. Turn off all the
electrical devices when they are not in
use. After using, we should dispose them
wiselyto reduce environmental pollution.
Electric cells contain corrosivechemicals and should not be thrown into
dustbins. They should be collected and
buried underground.
5 8 INNOVATIVE EFFORTS IN THE DESIGN OF
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5.8 INNOVATIVE EFFORTS IN THE DESIGN OF
EQUIPMENT USING CHEMICAL REACTIONS AS
SOURCES OF ENERGY
Fuel cells are electric cells which does not
run down or require recharging.
A hydrogen fuel cell uses hydrogen as fuel
to react with oxygen to produce energy.
The product is water which will not
pollute the environment.
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
1. Which of the following involve chemical
changes?
I. Lighting a match
II. Hard-boiling an eggIII. Melting tin to cast tin bars
A. I and II
B. I and III
C. II and III
D. I, II and III
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
2. Which of the following statements about a
chemical which undergoes physical
changes is not true?
A. Its size is changedB. Its state is changed
C. Its shape is changed
D. Its chemical properties are changed
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
3. Why does the temperature rise in a
chemical reaction?
A. The reaction is fast
B. The reaction is slow
C. The reaction absorbs heat energy
D. The reaction releases heat energy
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
4. The table below shows the result of an
experiment to study the reactivity of
metals X, Y and Z with water and steam.
Based on the observation, put these
metals in order of reactivity. Start with the
most reactive metal.
Metal Reaction withWater Steam
X No Yes
Y No No
Z Yes Yes
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
A. X, Y, ZB. Y, X, Z
C. Z, X, Y
D. Y, Z, X
CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
5. Which of the following metals can be
extracted from their ores by heating their
oxides with carbon?
I. Tin
II. Iron
III. Zinc
A. I and II onlyB. I and III only
C. II and III only
D. I, II and III
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
6. Lead can be obtained by heating a
mixture of lead oxide and carbon. This
reaction takes place because carbon
A. is a fuelB. acts as a catalyst
C. is more reactive than lead
D. is a non-metal whereas lead is a metal
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
7.
Browngas
Grey
solid
Moltenlead
bromide
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
When the switch is turned on, what can be
observed?
I. The bulb lights up
II. Brown gas is given off at the anodeIII. A grey solid is deposited at the cathode
A. I only
B. I and II only
C. II and III only
D. I, II and III only
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
8. Which of the following is true about
electroplating an iron key with silver?
A. The key is used as the anode
B. A small current is usedC. A silver plate is used as the cathode
D. Copper sulphate solution is used as the
electrolyte
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CHAPTER 5: ENERGY AND CHEMICAL CHANGES QUIZ
10. Photosensitive chemicals are stored indark bottles because they are sensitive
to
A. heatB. light
C. water
D. oxygen
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