EXTRACTION AND USES OF METALS [dchemlc]

Which one of the following metals cannot be found native?

• iron

• silver

• copper

• gold

Answer explanation

A few very unreactive metals, such as gold, are found native. That means that they exist naturally as the uncombined element. Silver and copper are also sometimes found native, although much more rarely.

iron is commonly extracted from its ore.

Sulfides such as sphalerite (zinc blende), ZnS, can be easily converted into an oxide by heating in air. This process is known as;

• roasting

• extracting

• oxidation

• reduction

Answer explanation

Many ores contain either oxides or compounds that are easily converted to oxides. Sulfides such as sphalerite (zinc blende), ZnS, can be easily converted into an oxide by heating in air, a process known as roasting.

2ZnS(s) + 30₂(g) --------> 2ZnO(s) + 2S0₂(g)

Iron can be extracted from its ore by heating with carbon. What are the products of this reaction?

Fe₂0₃(s) + 3C(s) --------->

• Fe

• CO

• CO₂

• Fe₃O₄

Answer explanation

Fe₂0₃(s) + 3C(s) ---------> 2Fe(I) + 3CO(g)

Carbon is higher in the reactivity series than iron and will take the oxygen away from the iron oxide. This is a redox reaction; the Fe₂0₃ is reduced to Fe in the reaction and the C is oxidized to CO.

What is the main reducing agent in the extraction of iron?

• carbon monoxide

• carbon dioxide

• iron

• carbon

Answer explanation

The extraction of iron is carried out in a blast furnace. The process is a bit more complicated than we have shown here. Other reactions also occur and the main reducing agent is actually carbon monoxide:

Fe₂0₃(s) + 3CO(g) --------> 2Fe(I) + 3C0₂(g)

What is the method commonly used to produce metals above zinc in the reactivity series?

• Electrolysis

• Reducing with carbon

• Fractional distillation

• Heating to high temperatures

Answer explanation

Ores of metals higher in the reactivity series than zinc can't be reduced using carbon at reasonable temperatures. This is because the metals are more reactive than carbon and therefore carbon cannot take the oxygen away from the metal oxide. Metals above zinc are usually produced by electrolysis.

Which of the following metals are mixed to make brass?

• copper

• zinc

• steel

• iron

Answer explanation

brass is an alloy and it is a mixture of copper and zinc.

Which of the following is not an alloy?

• bronze

• steel

• cupronickel

• tin

Answer explanation

An alloy is a mixture of a metal with, usually, other metals or carbon.

e.g. bronze (a mixture of copper and tin)

cupronickel (mixture of copper and nickel)

brass (mixture of copper and zinc)

steel (alloy of iron with carbon.)

Which of the following is not a use of mild steel?

• Nails

• Ship building

• Car bodies

• Electricity cables

Answer explanation

Mild steel is the name given to an alloy of iron containing up to about 0.25% of carbon.

It is used for nails, car bodies, ship building, girders and bridges.

aluminium is commonly used for electricity cables

Which of the following elements is not used to make stainless steel?

• nickel

• iron

• chromium

• aluminium

Answer explanation

Stainless steel is an alloy of iron with chromium and often nickel. Chromium forms a strong oxide layer in the same way as aluminium, and this oxide layer protects the iron as well.

What is the percentage of carbon mixed with iron to produce high-carbon steel?

• 0.6-1.2%

• 0.2-1.6%

• 0.25%

• 25%

Answer explanation

High-carbon steel is iron containing about 0.6-1.2% carbon (these amounts are variable)