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Starter1. What is a blast furnace used for?
2. What 3 solid raw materials are added to the blast furnace?
3. Which other reactant is added to the blast furnace?
4. What is the name and formula of the main iron ore?
5. Which gas actually reduces the iron oxide?
To extract iron from iron ore.
Iron ore, coke and limestone.
Hot air.
Iron (III) Oxide, Fe2O3.Carbon monoxide, CO.
Aims1. Discuss alloys and their uses.
2. Work through examples of percentage composition calculations.
3. Work through examples of empirical formula calculations.
AlloysThe properties of metals can be improved by making them into alloys.
An alloy is a mixture of metals or of metals with non-metals.
Alloys are usually made by melting the elements that make it up and then allowing it to cool until it has solidified.
Uses of alloys
Name of alloy Metals present Uses
Brass Copper and zinc Door handles
and fittings.
Bronze Copper and Tin Statues
Solder Tin and Lead Joining metals together.
Stainless Steel Iron, Chromium and Nickel.
Cutlery, kitchen sinks.
Percentage CompositionIt is important for chemists to know the percentage of each element in a compound.
The equation we use for doing this is :
% mass of element in a compound
=Mass of element in compound
Formula mass of compoundX 100
For example:
1. Work out the percentage of iron in iron (III) oxide.
==112
160 X 100 70%
STEP 1: Formula Fe2O3 or (Fe3+)2(O2-)3
STEP 2: Formula mass (2 x Fe) + (3 x O)
(2 x 56) + (3 x 16)
= 112 + 48 = 160
STEP 3: Mass of Fe in formula 2 x 56 = 112
X 100STEP 4: % of iron in compound = mass of iron in compound
mass of compound
For example:Ammonium nitrate, NH4NO3, is used as a fertiliser. Find the percentage composition of nitrogen in this compound.
==28
80 X 100 35%
STEP 1: Formula NH4NO3
STEP 2: Formula mass = (2 x N) + (4 x H) + (3 x O)
(2 x 14) + (4 x 1) + (3 x 16) = 80
STEP 3: Mass of N in formula 2 x 14 = 28
X 100STEP 4: % of N in compound = mass of N in compound
mass of compound
Percentage Composition Questions1. Calculate the percentage of hydrogen in ammonium
nitrate, NH4NO3.
2. Calculate the percentage of oxygen in ammonium nitrate, NH4NO3.
3. Calculate the percentage of hydrogen in water.
4. Calculate the percentage of sulphur in sulphur dioxide.
5%
60%
11.1%
50%
Empirical FormulaThe empirical formula of a compound gives the simplest ratio of the atoms present in that compound.
For example, ethane has the molecular C2H6.
The ratio of carbon atoms to hydrogen atoms is 2:6 and so the simplest ratio for this is 1:3.
That means that the empirical formula for this is CH3.
The empirical formula is obtained by calculating the simplest ratio of the atoms present in the compound.
Q. Calculate the empirical formula of a compound containing 1.84g of sodium, 1.28g of sulphur and 2.56g of oxygen.
Therefore the empirical formula is Na2S1O4, or simply Na2SO4.
Step 1:
Elements
Step 2: Mass
Step 3: RAM
Step 4: No. of moles
Step 5: Divide by smallest moles
Na S O
1.84 1.28 2.56
23 32 16
0.08/0.04 = 2
0.04/0.04 = 1
0.16/0.04 =4
n=1.84/23= 0.08
n=1.28/32=0.04
n=2.56/16= 0.16
Q. 6.40g of iron oxide was found to contain 4.48g of iron. Calculate the empirical formula for the iron oxide
We cannot have fractions of atoms and so therefore the empirical formula is Fe2O3.
Step 1:
Elements
Step 2: Mass
Step 3: RAM
Step 4: No. of moles
Step 5: Divide by smallest moles
Fe O
4.48 1.92
56 16
0.08/0.08 = 1
(1x2= 2)
0.12/0.08 = 1.5
(1.5x2=3)
n=4.48/56 =0.08
n=1.92/16 =0.12
Questions on Empirical Formula1. Calculate the empirical formula of the compound
which contains 1.08g of aluminium combined to 0.96g of oxygen.
2. Calculate the empirical formula of the hydrocarbon 0.60g of carbon and 0.15g of hydrogen.
3. Calculate the empirical formula for the compound containing 6.21g of lead combined to 7.62g of iodine.
Al2O3
CH3
PbI2