Ions and Electrolysis

Ions are charged particles formed when atoms lose or gain electrons: lose electrons for cations (+), gain them for anions (−). When current runs through an electrolyte, cations move to the cathode and anions to the anode, and reactions occur at each electrode. A substance that splits into ions in water is an electrolyte; sugar water makes no ions, so little current flows. On this page, change the voltage to watch ions move in electrolysis.

What are Ions?

⚡ Intuition — Atoms That Lost or Gained Electrons

①Atom loses e⁻ → cation (+): Na → Na⁺

②Atom gains e⁻ → anion (−): Cl → Cl⁻

③Ions carry charge so they respond to electric forces

Electrolysis Experiment

Voltage6 V

🔬 Electrolysis Principle

①Pass current through electrolyte solution

②Cations (+) go to the cathode (−)

③Anions (−) go to the anode (+)

④Redox reactions happen at each electrode

⑤Higher voltage → faster reaction

Electrolyte vs Non-electrolyte

💧 What Conducts Electricity

①Electrolyte: dissolves into ions → conducts (saltwater, HCl)

②Non-electrolyte: dissolves but no ions → does NOT conduct (sugar water, alcohol)

③Pure water barely conducts

Summary

Ion Formation

Cation: lose e⁻ (+) / Anion: gain e⁻ (−)

Na → Na⁺ + e⁻, Cl + e⁻ → Cl⁻

Electrolysis

Cation → cathode, Anion → anode

Pass current through electrolyte to decompose substances

🎯 Exam Points

①Cations (+) → cathode (−)

②Anions (−) → anode (+)

③Electrolyte = substance that splits into ions

④Cathode: reduction (gain e⁻), Anode: oxidation (lose e⁻)

⑤Water electrolysis: H₂ at cathode, O₂ at anode (2:1 by volume)

Examples and Unit Test

Example 1

When a sodium atom (Na) and a chlorine atom (Cl) each become ions, do they lose or gain an electron, and what ion does each become? Show it as an equation.

Sodium loses one electron and becomes a cation: Na → Na⁺ + e⁻.

Chlorine gains one electron and becomes an anion: Cl + e⁻ → Cl⁻.

▸ Na → Na⁺ + e⁻ (cation) / Cl + e⁻ → Cl⁻ (anion)

Losing an electron makes a cation (+); gaining one makes an anion (−).

Example 2

When water is electrolyzed, which gas forms at each electrode, and what is the volume ratio of the two gases?

Hydrogen gas (H₂) forms at the cathode (−) and oxygen gas (O₂) forms at the anode (+).

Following the hydrogen-to-oxygen ratio in a water molecule (H₂O), the volume ratio of hydrogen to oxygen is 2 : 1.

▸ Cathode = hydrogen, anode = oxygen / volume ratio hydrogen : oxygen = 2 : 1

In electrolysis, cations move to the cathode and anions to the anode to react.

Unit Test

Which statement about ions and electrolysis is correct?

①When an atom loses an electron it becomes an anion

②In electrolysis cations move to the anode

③An electrolyte dissolves in water, splits into ions, and lets current flow

④Sugar water is an electrolyte that conducts current well

⑤Electrolyzing water gives a hydrogen-to-oxygen volume ratio of 1 : 2

▸ ③ An electrolyte dissolves in water, splits into ions, and lets current flow

Losing an electron makes a cation (① wrong), and in electrolysis cations move to the cathode (② wrong).

Sugar water is a non-electrolyte that forms no ions (④ wrong), and electrolyzing water gives hydrogen : oxygen = 2 : 1 (⑤ wrong); an electrolyte dissolves in water, splits into ions, and lets current flow (③ correct).

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Gas Reaction Law

Acid-Base Reactions

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