Today in Chemistry, I learn about Electrolysis.
Electrolysis is when ionic substances is broken down by using electricity.
Ionic substances form when a metal reacts with a
non-metal. They contain charged particles called ions. For example, sodium chloride
forms when sodium reacts with chlorine. It contains positively charged sodium
ions and negatively charged chloride ions. In
electrolysis, the ions are free to move because it is dissolved in water. For
example, if electricity is passed through copper chloride solution, the copper
chloride is broken down to form copper metal and chlorine gas.
In electrolysis, there are two
electrodes. The negative electrode is the cathode while the positive electrode
is the anode. The cathode attracts positive ions while the anode attracts
negative ions. In the negative electrode, they gain electrons and are reduced
while in the positive electrode, they lose electrons and get oxidised.
In the negative electrode, the ions who
will escape the solution depends on which one is less reactive. The less
reactive one will escape while the more reactive one will stay in the solution.
In electrolysis, electrons are shown as
e-. This is a half equation. A half equation is use to show what
happens in the electrodes. A
half-equation is balanced by adding, or taking away, a number of electrons
equal to the total number of charges on the ions in the equation.
Positive ions gain electrons at
the negative electrode, so are reduced.
- In aluminum extraction: Al3+ + 3e-
→ Al
- In copper purification: Cu2+ + 2e-
→ Cu
- Electrolysis of sodium chloride solution: 2H+
+ 2e- → H2
Negative ions or neutral atoms
lose electrons at the positive electrode and are oxidised. For example,
chlorine is produced during the electrolysis of sodium chloride solution:
2Cl- - 2e-
→ Cl2
This half-equation can be
rewritten as 2Cl- → Cl2 + 2e-
- In aluminum extraction: 2O2- → O2
+ 4e-
- In copper purification: Cu → Cu2++
2e-
The simulation below shows what
happens during the purification of copper by electrolysis.
