c5 calculating the mass of a metal1

7/30/2019 C5 Calculating the Mass of a Metal1

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Studydoctor 2010

Lesson 9: Calculating the mass of a metal

When scientist are trying to obtain a metal from its ore, they need to know how

much of the metal they will obtain from the oxide.

For example, if you have 200kg of iron oxide (rust) how much iron will you

obtain through the process of reduction? Well there are four steps that you need

to undertake:

1. Write down the formula of the ore: The formula of iron oxide is Fe2O3.2. Calculate the relative formula mass: In Fe2O3 there are 2 atoms of

iron and 3 atoms of oxygen. Iron has a relative atomic mass of 56 and

oxygen has a relative atomic mass of 16.

This means that iron oxide has a relative formula mass of:

Fe2O3

(256) + (316) = 160.

3. Calculate the percentage mass of the metal present: The percentagemass of the metal can be calculated using the equation:

There are 2 atoms of iron in iron oxide, which have a relative mass of

256 = 112. This means that the percentage mass of iron in iron

oxide is:

lllllllllllll

4. Calculate the mass of the metal obtained:Since we know that eachmolecule of iron oxide will contain 70% iron, then we multiply the mass

we have by the percentage mass to get the mass of iron we will obtain.

What you need to know:

1. How to calculate the mass of a metal that can be removed from an oxide.


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This means that since we have 200 kg of iron and a percentage mass

of 70% then we can calculate the mass of iron we would obtain:

200 kg 70% = 140kg of iron.

In your exam you may be asked to calculate the mass of a metal obtained fromits ore.

A common example is the reduction of zinc oxide. If we have 100 kg of zinc

oxide, how much zinc will be formed when zinc oxide is reduced?

1. Zinc oxide has a formula of ZnO.2. Zinc oxide contains 1 atom of Zinc and 1 atom of oxygen. Zinc has a

relative atomic mass of 65 and oxygen has a relative atomic mass of 16.

So ZnO has a relative formula mass of:

ZnO

65 + 16 = 81.

3. The percentage mass of zinc in zinc oxide is:

llllllllllllll

4. The mass of metal that will be obtained will be:100 kg 80% = 80kg

Another common example is the reduction of aluminium oxide. If we have 500kg

of aluminium oxide, how much aluminium will be formed when the aluminium

oxide is reduced?

1. Aluminium oxide has a formula of Al2O3.2. Aluminium oxide contains 2 atoms of aluminium and 3 atoms of oxygen.

Aluminium has a relative atomic mass of 27 and oxygen has a relative

atomic mass of 16. So Al2O3 has a relative formula mass of:

Relative atomic mass of Zinc

Relative formula mass of ZnO


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Al2O3

(2 27) + (3 16) = 102.

3. The percentage mass of aluminium in aluminium oxide is:

lllllllllllll

4. The mass of metal that will be obtained will be:500kg 53% = 265 kg

In your exam you may be asked to calculate the mass of a metal from its ore.

Recap:

To calculate the amount of a metal that can be produced from its ore you need to:

1. Write down its formula.2. Calculate its relative formula mass.3. Calculate the percentage mass of the metal present.4. Calculate the mass of the metal obtained.

Relative atomic mass of Aluminium

Relative formula mass of Al2O3

c5 calculating the mass of a metal1

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