What it shows
A more reactive metal pushes a less reactive metal out of its salt solution. Iron displaces copper from copper sulphate, and the mass of copper formed can be compared with the mass of iron used.
The science
Iron is higher in the reactivity series than copper. In the reaction Fe + CuSO4 gives FeSO4 + Cu, each iron atom loses two electrons and goes into solution as Fe2+, while each Cu2+ ion gains two electrons and sticks to the nail as copper metal. The blue colour of Cu2+ fades to pale green as Fe2+ forms. Copper atoms are heavier than iron atoms, so the nail gains mass for each atom swapped, by a ratio of 63.5 to 56. Copper wire does not react because copper is not more reactive than copper.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A clean iron nail, about 5 to 6 g (rub with sandpaper)
- Copper sulphate crystals, 5 g (from an agri or lab supply shop)
- A glass of 100 ml and warm water
- A scale reading to 0.01 g if possible (a jeweller can weigh it)
- A strip of aluminium foil and a piece of copper wire for comparison
- Paper towel
- A spoon and a notebook
Safety
For this project: An adult must supervise. Copper sulphate is harmful if swallowed and irritates eyes and skin, so wear gloves and goggles and keep it away from food and children. Pour waste into a labelled container for the teacher, not down the drain.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Dissolve 5 g of copper sulphate in 100 ml of warm water to make a clear blue solution.
Clean the nail with sandpaper until it is shiny, wash it, dry it and weigh it. Record the mass.
Put a copper wire and a piece of foil into two other glasses of the same solution as comparison tests.
Lower the nail into the blue solution. Photograph or sketch it every five minutes for 30 minutes.
Leave it for 24 hours so that more copper coats the nail. Note the colour of the liquid.
Lift the nail carefully with tongs or a spoon, rinse it gently in water and dry it on paper without rubbing off the brown coating.
Weigh the dry nail and calculate the change in mass. A common mistake is to scrub the copper off before weighing.
Compare the three glasses and write which metals reacted and which did not.
What you should see
The iron nail becomes coated in reddish-brown copper and the solution fades from blue to pale green, while the copper wire shows no change. The dried nail is a little heavier than at the start.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the nail turn brown?
Copper metal is deposited on it as copper ions gain electrons.
2Why does the blue colour fade?
Blue Cu2+ ions are used up and pale green Fe2+ ions form.
3Why does the nail gain mass even though iron dissolves?
Each iron atom dissolved is replaced by a heavier copper atom on the nail.
4What is the use of this idea in industry?
The reactivity series decides how metals are extracted and how metals are used to protect each other from corrosion.
Take it further
Test a zinc strip, a magnesium ribbon and a piece of tin foil in the same solution and rank the metals from most to least reactive.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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