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Extracting Metals with Carbon

Worksheet Overview

QUESTION 1 of 10

Metals are incredibly useful. A very few unreactive metals are found in nature in metallic form (called native metals), like these tiny nuggets of gold;

Unfortunately, most metals react with oxygen in the air- so we find ores instead. Ores are rocks made of compounds containing large amounts of a metal. Most of the time, these compounds are oxides. For example, iron ore commonly contains magnetite (Fe3O4) or hematite (Fe2O3). There is plenty of iron ore in the world...

... but how can we extract the iron (extracting a metal from its ore is called smelting)?

The answer was discovered- probably by accident- about 8000 years ago. Stone age people found that putting certain rocks in a wood fire produced metals. The first metals discovered this way were lead and tin, but the basic idea works for copper and iron as well. Iron is the most important metal in modern engineering, so let's think about that.

Iron is more reactive than gold, but it's not that reactive. In particular, iron is less reactive than carbon. That means that we can do a displacement reaction;

iron oxide + carbon → iron + carbon dioxide
 
The same principle works for all metals which are less reactive than carbon. The metals commonly extracted from oxides by this method are zinc, iron, tin and copper. We don't usually need to extract silver or gold from ores, because they are usually found as native metals.

This method doesn't work for more reactive metals. Carbon isn't reactive enough to displace aluminium or magnesium from their oxides. The only way to extract these metals from their oxides is electrolysis.

How do we smelt iron?
The basic idea of smelting hasn't changed since ancient times. We take iron ore, and heat it with carbon. The carbon is both the fuel to produce the heat, and the reducing agent for the ore.

A modern blast furnace uses a version of the same process, optimised to efficiently produce iron with low levels of impurities. To do this, the temperature inside the furnace is about 1500 °C. At these temperatures, the reduction of iron becomes a two-stage process. First, carbon reacts with oxygen to make carbon monoxide;
2 C + O2 → 2 CO
Then the carbon monoxide reacts with iron ore to produce iron and carbon dioxide;
Fe2O3 + 3 CO → 2 Fe + 3 CO2

Oxidation and reduction
The idea of reduction came from the conversion of metal ores into metals. By driving the oxygen atoms off an ore, we reduce its mass; the mass of a lump of iron will be less than the mass of the iron oxide it came from. In hematite, the iron is Fe3+ ions. To turn these into metallic iron atoms, iron needs to gain electrons (OILRIG- oxidation is loss (of electrons), reduction is gain (of electrons));

2 Fe3+ + 6 e- → 2 Fe

Carbon monoxide is oxidised;

3 CO → 6 e- + 3 CO2+
The positive carbon monoxide ions then react with the negative oxygen ions left over from the hematite to make neutral carbon dioxide.


We can extract several important metals- copper, tin, iron and zinc from ores by heating the ore with carbon. Whatever the details, this works by a displacement reaction; carbon displaces the metal from the oxide to produce carbon dioxide. Because this process works by a displacement reaction, it only works for metals which are less reactive than carbon. For more reactive metals, we need to use electrolysis.

Pick two half-sentences to make a complete sentence about native metals.

Which of these are good ores of iron? Tick all the correct answers.

SiO2

Fe2O3

FeCO3

Fe3O4

NaAl0.95Fe0.05Si3O8

What is the name of the process which extracts metals from an ore by heating with carbon?

What type of reaction is this?

iron oxide + carbon → iron + carbon dioxide

displacement reaction

heating reaction

reactive reaction

Which of these metals can we extract from ores by heating with carbon?

aluminium

copper

iron

potassium

tin

Which two of these phrases describes the reduction of an ore?

The ore gains mass

The ore loses mass

The metal in the ore gains electrons

The metal in the ore loses electrons

Zinc oxide is ZnO. Which of these is a balanced symbol equation for the smelting of zinc oxide?

ZnO + C → Zn + CO2

ZnO + 2 C → Zn + CO2

2 ZnO + 2 C → 2 Zn + CO2

2 ZnO + C → 2 Zn + CO2

We can extract tin from tin oxide by heating the oxide with carbon. What can we conclude from this?

tin is more reactive than carbon

tin is less reactive than carbon

tin is more reactive than oxygen

carbon is more reactive than oxygen

In the reaction 

Fe2O3 + 3 CO → 2 Fe + 3 CO2

what is oxidised and what is reduced?

tin is more reactive than carbon

tin is less reactive than carbon

tin is more reactive than oxygen

carbon is more reactive than oxygen

Look at these data for different metals.

metal cost of 1 kg (£) amount in Earth's crust (%)
aluminium 1.30 8
iron 0.30 5
tin 13.00 0.0002

Complete this paragraph about these three metals. Use the words aluminium, iron and tin.

tin is more reactive than carbon

tin is less reactive than carbon

tin is more reactive than oxygen

carbon is more reactive than oxygen

  • Question 1

Pick two half-sentences to make a complete sentence about native metals.

CORRECT ANSWER
EDDIE SAYS
Native metals are the ones found in their metallic form, not in an ore. This normally only happens for very unreactive metals, such as silver and gold.
  • Question 2

Which of these are good ores of iron? Tick all the correct answers.

CORRECT ANSWER
Fe2O3
FeCO3
Fe3O4
EDDIE SAYS
Most iron ore is some sort of iron oxide, but iron ore doesn't have to be just iron and oxygen. Iron ores have to contain enough iron to be worth processing, which is why NaAl0.95Fe0.05Si3O8 isn't much good; the iron content is tiny.
  • Question 3

What is the name of the process which extracts metals from an ore by heating with carbon?

CORRECT ANSWER
smelt
smelting
EDDIE SAYS
"Smelting" sounds a bit like special melting... that's probably not where the word came from, but it will do for us remembering it.
  • Question 4

What type of reaction is this?

iron oxide + carbon → iron + carbon dioxide

CORRECT ANSWER
displacement reaction
EDDIE SAYS
This is a displacement reaction; the carbon is displacing the metal from the oxide, to make carbon dioxide. That's good for us, because it isolates the metal, which is what we want.
  • Question 5

Which of these metals can we extract from ores by heating with carbon?

CORRECT ANSWER
copper
iron
tin
EDDIE SAYS
The metals commonly extracted from oxides by heating are zinc, iron, tin and copper. Aluminium is too reactive (carbon can't displace it), and potassium is even more reactive than aluminium.
  • Question 6

Which two of these phrases describes the reduction of an ore?

CORRECT ANSWER
The ore loses mass
The metal in the ore gains electrons
EDDIE SAYS
Start with OILRIG- reduction is loss of electrons. That means that oxygen is lost from the ore, leaving pure metal behind. That has the effect of reducing the mass of the lump of ore.
  • Question 7

Zinc oxide is ZnO. Which of these is a balanced symbol equation for the smelting of zinc oxide?

CORRECT ANSWER
2 ZnO + C → 2 Zn + CO2
EDDIE SAYS
To make 1 unit of CO2, we need two oxygen atoms. That means we need two units of ZnO, which means we will produce 2 atoms of metallic zinc. Then, everything balances.
  • Question 8

We can extract tin from tin oxide by heating the oxide with carbon. What can we conclude from this?

CORRECT ANSWER
tin is less reactive than carbon
EDDIE SAYS
Tin must be less reactive than carbon, because carbon ends up in the compound with oxygen.
  • Question 9

In the reaction 

Fe2O3 + 3 CO → 2 Fe + 3 CO2

what is oxidised and what is reduced?

CORRECT ANSWER
EDDIE SAYS
The metal gets reduced in these reactions. The electrons have to go somewhere, so they go to the other reactant.
  • Question 10

Look at these data for different metals.

metal cost of 1 kg (£) amount in Earth's crust (%)
aluminium 1.30 8
iron 0.30 5
tin 13.00 0.0002

Complete this paragraph about these three metals. Use the words aluminium, iron and tin.

CORRECT ANSWER
EDDIE SAYS
A lot of the clues to answering this question were in the table. If you are given data in a question, expect to use them. The other point here is that we use heating with carbon where possible, because it is much cheaper.
---- OR ----

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