Chemistry Reflection 11

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: 2O^2- → O₂ + 4e^-
• In copper purification: Cu → Cu²⁺+ 2e^-

The simulation below shows what happens during the purification of copper by electrolysis.