Iron and Copper Sulfate Solution:
A pocket knife blade which has been dipped in copper sulphate solution comes out with a pinkbrown coating. This coating is copper but the layer is easily removed.
The same thing happens with a nail in copper sulphate, but overnight other observations can be
made. There are few reactions in which all reactants and products can be identified. This is
one of them and worth exploring to the full.
a.
b.
c.
d.
e.
Attach a piece of cotton or thin wire to a cleaned 6 to 10 cm nail,
Place this into a test tube containing copper sulfate (only half nail submerged)
Remove nail after a few seconds and observe, record and explain
Cu2+ + 2e
Cu
Replace the nail into the copper sulfate and leave overnight
Observe test tube and record, then remove nail and wash under tap to remove
loose solids, and record
FOUR observations can be made:
1. brown solid formed
2. blue colour gone
3. thinner nail
4. pale yellow/green solution**
deduce Cu formed
deduce all Cu2+ reacted
some Fe reacted
deduce Fe2+ formed
** obtain some aqueous iron II and iron III ion and add dilute NaOH.
Iron II gives green/black precipitate, iron III gives rust brown precipitate
Solution from test tube gives a greenish precipitate
Explanation:
a) the iron clearly reacts, so must lose electrons
Fe
- 2e
Fe2+
b) the electrons which the iron loses must go somewhere (they cannot just disappear)
Cu2+
+ 2e
Cu
These two processes can be combined to give a total equation. Since this shows only the reacting
particles it's called an IONIC EQUATION
The sulphate ion is not included as it doesn't take part in the reaction
Fe
+
Cu2+
Fe2+ +
Cu
This example shows that of the two metals, copper and iron, iron 'wants' to 'give away' its electron
and 'forces' copper ions to 'accept' the electrons. This is as expected from the reactivity series.
This means that iron is a STRONGER REDUCING AGENT than copper.
Iron-Copper Sulfate R.B.Jansen MGS