IGCSE Chemistry Term 2 Lesson 9: Electrolysis
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Questions and Answers

What is electrolysis?

Electrolysis is the breakdown of a compound using an electrical current.

Why are solid ionic and covalent compounds not conductive?

Solid ionic and covalent compounds are not conductive because the charge can't move.

What allows graphite to conduct electricity?

Graphite conducts electricity because it has free electrons.

Why can hydrogen halides be electrolysed even though they are covalent?

<p>Hydrogen halides can be electrolysed in aqueous solution because they become ionic with positive and negative ions free to move.</p> Signup and view all the answers

What happens when electrodes are placed in a molten ionic substance?

<p>The positive ion (cation) will be attracted to the cathode, and the negative ion (anion) will be attracted to the anode.</p> Signup and view all the answers

What are the names of the two electrodes used in electrolysis of molten ionic compounds?

<p>The positively charged electrode is called an anode, and the negatively charged electrode is called the cathode.</p> Signup and view all the answers

What product will form at the cathode if the metal is less reactive than hydrogen?

<p>Solid metal</p> Signup and view all the answers

What product will form at the anode if no halides are present?

<p>Oxygen gas (O2)</p> Signup and view all the answers

What products will form at the electrodes when electrolysing pure water?

<p>Hydrogen gas (H2) at the cathode, oxygen gas (O2) at the anode</p> Signup and view all the answers

What are the key components formed by the electrolysis of water?

<p>Hydrogen ions (H+), hydroxide ions (OH-), hydrogen gas (H2), and oxygen</p> Signup and view all the answers

What determines which product will form at the cathode during electrolysis?

<p>Reactivity of the metal with a reactivity series</p> Signup and view all the answers

What will form at the anode if a halide is present?

<p>Molecules of the halogen (e.g., Cl2, Br2, I2)</p> Signup and view all the answers

What is the term used for the liquid or solution that undergoes electrolysis?

<p>Electrolyte</p> Signup and view all the answers

What are the common materials for electrodes?

<p>Carbon and platinum</p> Signup and view all the answers

What will form at the cathode when electrolysing copper(ll) sulfate?

<p>Copper</p> Signup and view all the answers

What product will form at the anode when electrolysing dilute sulfuric acid?

<p>Oxygen</p> Signup and view all the answers

What allows hydrogen halides to be electrolyzed even though they are covalent?

<p>Aqueous solution turns covalent hydrogen halides into ionic compounds with positive and negative ions free to move.</p> Signup and view all the answers

What determines which product will form at the cathode during electrolysis?

<p>The reactivity of the metal compared to hydrogen determines the product formed at the cathode during electrolysis.</p> Signup and view all the answers

Why can graphite conduct electricity despite being covalent?

<p>Graphite can conduct electricity because it has free electrons.</p> Signup and view all the answers

What is the term for the liquid or solution that undergoes electrolysis?

<p>The liquid or solution that undergoes electrolysis is called the electrolyte.</p> Signup and view all the answers

What happens when electrodes are placed in a molten ionic substance?

<p>The positive ion (cation) is attracted to the cathode, and the negative ion (anion) is attracted to the anode.</p> Signup and view all the answers

What are the common materials used for electrodes?

<p>Common materials for electrodes include graphite and metals like platinum or gold.</p> Signup and view all the answers

What products form at the anode and cathode during the electrolysis of lead(ll) bromide (PbBr2)?

<p>Cathode: Lead (Pb); Anode: Bromine (Br2)</p> Signup and view all the answers

What product forms at the anode during the electrolysis of dilute sulfuric acid (H2SO4)?

<p>Oxygen gas (O2)</p> Signup and view all the answers

What product will form at the cathode if the metal is less reactive than hydrogen during electrolysis?

<p>Solid metal</p> Signup and view all the answers

What determines the product formed at the anode during the electrolysis of an aqueous solution?

<p>Presence of halides</p> Signup and view all the answers

What product forms at the cathode during the electrolysis of copper(ll) sulfate (CuSO4)?

<p>Copper</p> Signup and view all the answers

What product forms at the cathode if the metal is the same or more reactive than hydrogen?

<p>Hydrogen gas (H2)</p> Signup and view all the answers

What is the term used for the liquid or solution that undergoes electrolysis?

<p>Electrolyte</p> Signup and view all the answers

What product forms at the anode during the electrolysis of water?

<p>Oxygen gas (O2)</p> Signup and view all the answers

Why can hydrogen halides be electrolyzed even though they are covalent?

<p>They form ions in solution</p> Signup and view all the answers

What are the common materials for electrodes in electrolysis?

<p>Carbon and platinum</p> Signup and view all the answers

Flashcards

Electrolysis

The process of using an electrical current to break down a compound.

Why are solid ionic and covalent compounds non-conductive?

Solid ionic and covalent compounds do not conduct electricity because their charged particles are locked in a fixed position and cannot move freely.

Why can graphite conduct electricity?

Graphite can conduct electricity because it has delocalized electrons that can move freely throughout its structure.

Why can hydrogen halides be electrolyzed?

Although hydrogen halides are covalent, they become ionic in aqueous solution, creating free-moving positive and negative ions that allow for electrolysis.

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Electrodes in molten ionic substances

When electrodes are placed in a molten ionic substance, the positive ions (cations) are attracted to the negatively charged electrode (cathode), and the negative ions (anions) are attracted to the positively charged electrode (anode).

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Anode

The positively charged electrode in electrolysis is called the anode.

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Cathode

The negatively charged electrode in electrolysis is called the cathode.

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Product at the cathode (less reactive metal)

If the metal is less reactive than hydrogen, solid metal will be formed at the cathode during electrolysis.

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Product at the anode (no halides)

If no halides are present, oxygen gas (O2) will be formed at the anode during electrolysis.

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Electrolysis of pure water

The products formed during the electrolysis of pure water are hydrogen gas at the cathode and oxygen gas at the anode.

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Components formed during electrolysis of water

The key components formed during the electrolysis of water are hydrogen ions (H+), hydroxide ions (OH-), hydrogen gas (H2), and oxygen gas (O2).

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Factors influencing product at the cathode

The reactivity of the metal, compared to hydrogen, using a reactivity series, determines which product will form at the cathode during electrolysis.

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Product at the anode (halides)

If a halide is present, molecules of the halogen (e.g., Cl2, Br2, I2) will be formed at the anode during electrolysis.

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Electrolyte

The liquid or solution that undergoes electrolysis is called the electrolyte.

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Electrode materials

Common materials used for electrodes in electrolysis include carbon (graphite) and platinum.

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Product at the cathode (copper(II) sulfate)

Copper will be formed at the cathode during the electrolysis of copper(II) sulfate.

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Product at the anode (dilute sulfuric acid)

Oxygen gas (O2) will be formed at the anode during the electrolysis of dilute sulfuric acid.

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Why are hydrogen halides electrolyzed?

Hydrogen halides form ions in aqueous solution, allowing for electrolysis.

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Common electrode materials

Common materials for electrodes in electrolysis are carbon (graphite) and platinum.

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Electrolysis of lead(II) bromide

Lead (Pb) will form at the cathode, and bromine (Br2) will form at the anode during the electrolysis of lead(II) bromide.

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Product at the anode (dilute sulfuric acid)

Oxygen gas (O2) will form at the anode during the electrolysis of dilute sulfuric acid.

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Cathode product (less reactive metal)

A solid metal will form at the cathode during electrolysis if the metal is less reactive than hydrogen.

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Product at the anode (aqueous solution)

The presence of halides determines the product formed at the anode during the electrolysis of an aqueous solution.

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Product at the cathode (copper(II) sulfate)

Copper will form at the cathode during the electrolysis of copper(II) sulfate.

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Cathode product (reactive metal)

Hydrogen gas (H2) will form at the cathode if the metal is the same or more reactive than hydrogen.

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Electrolyte

The liquid or solution that undergoes electrolysis is called the electrolyte.

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Product at the anode (water)

Oxygen gas (O2) will be formed at the anode during the electrolysis of water.

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Reason for hydrogen halides being electrolyzed

They form ions in solution, enabling electrical conductivity and allowing for electrolysis.

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Common electrode materials

Common materials for electrodes in electrolysis include carbon (graphite) and platinum.

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Study Notes

What is Electrolysis?

  • Electrolysis is the process where an electric current is used to drive a chemical reaction.

Conductivity

  • Solid ionic and covalent compounds are not conductive because the ions or molecules are fixed in place and cannot move freely.
  • Graphite, a covalent compound, can conduct electricity due to its unique structure, which allows electrons to move freely.

Electrolysis of Molten Ionic Compounds

  • When electrodes are placed in a molten ionic substance, it allows the ions to move freely and conduct electricity.
  • The two electrodes used in electrolysis of molten ionic compounds are the anode (positive electrode) and cathode (negative electrode).

Products Formed at Electrodes

  • At the cathode, if the metal is less reactive than hydrogen, hydrogen gas is produced.
  • At the anode, if no halides are present, oxygen gas is produced.
  • During the electrolysis of pure water, hydrogen gas is produced at the cathode and oxygen gas is produced at the anode.
  • The key components formed by the electrolysis of water are hydrogen and oxygen.

Factors Determining Products

  • The product formed at the cathode during electrolysis is determined by the reactivity of the metal.
  • The product formed at the anode is determined by the presence of halides.

Electrolysis of Hydrogen Halides

  • Hydrogen halides can be electrolyzed despite being covalent due to the presence of ions in the solution.

Terms and Materials

  • The term used for the liquid or solution that undergoes electrolysis is the electrolyte.
  • Common materials used for electrodes are graphite, platinum, and copper.

Specific Electrolysis Reactions

  • During the electrolysis of copper(ll) sulfate, copper is produced at the cathode.
  • During the electrolysis of dilute sulfuric acid, oxygen is produced at the anode.
  • During the electrolysis of lead(ll) bromide, lead is produced at the cathode and bromine is produced at the anode.

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Test your knowledge on the concept of electrolysis in chemistry, focusing on the breakdown of compounds using an electrical current, conductive properties of different compounds, and key principles related to charged particles and conductivity.

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