Chemistry Chapter on Reactions and Electrolysis
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Questions and Answers

What is the primary characteristic of an exothermic reaction?

  • It transfers thermal energy to the surroundings. (correct)
  • It results in a decrease in the temperature of the surroundings.
  • It requires a catalyst to proceed.
  • It absorbs thermal energy from the surroundings.

What is the sign of the enthalpy change (∆H) for an endothermic reaction?

  • Positive (correct)
  • Varies depending on the reaction
  • Negative
  • Zero

Which of the following statements is true regarding activation energy (Ea)?

  • It is the total energy available in a chemical reaction.
  • It decreases as the concentration of reactants increases.
  • It is the energy required for particles to collide effectively. (correct)
  • It is the energy released during a reaction.

How is bond breaking characterized in terms of energy?

<p>It is an endothermic process that absorbs energy. (A)</p> Signup and view all the answers

When calculating the enthalpy change of a reaction using bond energies, which process is considered exothermic?

<p>The energy released during bond formation. (C)</p> Signup and view all the answers

During the electrolysis of molten lead(II) bromide, which substance is produced at the cathode?

<p>Lead (D)</p> Signup and view all the answers

In the electrolysis of concentrated aqueous sodium chloride, which product is formed at the anode?

<p>Chlorine gas (A)</p> Signup and view all the answers

What is formed at the cathode during the electrolysis of dilute sulfuric acid?

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

In the electrolysis of a binary compound, what is produced at the anode?

<p>Non-metal elements (D)</p> Signup and view all the answers

What purpose does electroplating serve for metal objects?

<p>To improve appearance and resistance to corrosion (C)</p> Signup and view all the answers

Which statement correctly describes hydrogen–oxygen fuel cells?

<p>They require oxygen and produce electricity with water as the only chemical product (D)</p> Signup and view all the answers

Which of the following is NOT a product of the electrolysis of aqueous copper(II) sulfate using copper electrodes?

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

What change occurs to the appearance of metal objects during electroplating?

<p>They gain a shiny finish (A)</p> Signup and view all the answers

Which chemical test confirms the presence of water by changing from blue to pink?

<p>Anhydrous cobalt(II) chloride (C)</p> Signup and view all the answers

What is the purpose of chlorination in the treatment of domestic water supply?

<p>To kill harmful microbes (B)</p> Signup and view all the answers

Why is distilled water preferred over tap water in practical chemistry?

<p>It has fewer chemical impurities (A)</p> Signup and view all the answers

Which harmful substance may be present in natural water sources that can lead to diseases?

<p>Sewage (B)</p> Signup and view all the answers

What negative impact do nitrates and phosphates have on aquatic life?

<p>They lead to deoxygenation of water (B)</p> Signup and view all the answers

What role does carbon play in the treatment of domestic water?

<p>To remove tastes and odors (A)</p> Signup and view all the answers

Which of the following substances is typically beneficial in water sources?

<p>Some metal compounds (B)</p> Signup and view all the answers

Which method is used to remove solids from the domestic water supply?

<p>Filtration (D)</p> Signup and view all the answers

Which substance is NOT a potential pollutant in natural water sources?

<p>Dissolved oxygen (B)</p> Signup and view all the answers

What is the first step in the treatment of the domestic water supply?

<p>Sedimentation (C)</p> Signup and view all the answers

What is the main ore of aluminium that is commonly used for extraction?

<p>Bauxite (A)</p> Signup and view all the answers

Which process is primarily used to extract aluminium from bauxite?

<p>Electrolysis (A)</p> Signup and view all the answers

Why must the carbon anodes in the electrolysis process be regularly replaced?

<p>They are oxidized and consumed during the reaction. (D)</p> Signup and view all the answers

What role does cryolite play in the extraction of aluminium?

<p>It lowers the melting point of alumina. (B)</p> Signup and view all the answers

During the electrolysis of aluminium oxide, what occurs at the cathode?

<p>Aluminium ions are reduced to form aluminium metal. (C)</p> Signup and view all the answers

What is the result of the thermal decomposition of calcium carbonate in the extraction process?

<p>Production of carbon dioxide and calcium oxide. (A)</p> Signup and view all the answers

What is the reaction that takes place when carbon dioxide is reduced to carbon monoxide during iron extraction?

<p>C + CO2 → 2CO (D)</p> Signup and view all the answers

What is the term for the compound formed when calcium oxide reacts with silicon dioxide?

<p>Calcium silicate (A)</p> Signup and view all the answers

In the electrolysis of aluminium oxide, which product is formed at the anode?

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

What is the primary purpose of the extraction processes for aluminium and iron?

<p>To obtain metals from their ores economically. (D)</p> Signup and view all the answers

What is defined as the decomposition of an ionic compound by the passage of an electric current?

<p>Electrolysis (C)</p> Signup and view all the answers

Which electrode is known as the positive electrode in an electrolytic cell?

<p>Anode (D)</p> Signup and view all the answers

During electrolysis, what happens to electrons at the anode?

<p>Loss of electrons (B)</p> Signup and view all the answers

What movement occurs within the electrolyte during electrolysis?

<p>Movement of ions (D)</p> Signup and view all the answers

In the context of electrolysis, what is the electrolyte primarily composed of?

<p>Molten or aqueous ionic substances (A)</p> Signup and view all the answers

What is the main function of the cathode in an electrolytic cell?

<p>To gain electrons and facilitate reduction (B)</p> Signup and view all the answers

Which of the following activities occurs at the cathode during electrolysis?

<p>Reduction of cations (A)</p> Signup and view all the answers

Which statement correctly describes the overall process during electrolysis?

<p>Electric current decomposes ionic compounds (A)</p> Signup and view all the answers

What is required for electrolysis to take place?

<p>Electric current and an ionic compound (C)</p> Signup and view all the answers

What is the role of the electric current in an electrolytic cell?

<p>To provide energy for ionic decomposition (A)</p> Signup and view all the answers

Flashcards

Exothermic reaction

A chemical reaction that releases heat energy to the surroundings, causing the temperature of the surroundings to increase.

Endothermic reaction

A chemical reaction that absorbs heat energy from the surroundings, causing the temperature of the surroundings to decrease.

Activation energy (Ea)

The minimum amount of energy that colliding particles must have to react.

Enthalpy change (∆H)

The energy change that occurs during a chemical reaction.

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Bond energy and Enthalpy change

The enthalpy change of a reaction can be calculated by considering the energy required to break bonds in reactants and the energy released when new bonds are formed in products.

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Electrolysis

The process of using an electric current to break down a compound into its elements. It's used to produce, for example, aluminum from aluminum oxide.

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Cathode

The negatively charged electrode in electrolysis. It's where reduction (gain of electrons) happens, usually forming metals or hydrogen.

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Anode

The positively charged electrode in electrolysis. It's where oxidation (loss of electrons) happens, usually forming non-metals (except hydrogen).

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Electroplating

The process of covering a metal object with a thin layer of another metal through electrolysis. It improves its appearance, protects it from corrosion, and can change its properties.

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Hydrogen-oxygen fuel cell

A device that converts chemical energy directly into electrical energy using hydrogen and oxygen as fuel. It produces water as the only by-product.

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Hydrogen-oxygen fuel cell

A specific type of electrochemical cell that uses the reaction between hydrogen and oxygen to generate electricity. Water is formed as a byproduct, making it an environmentally friendly energy source.

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Redox reaction

A type of chemical reaction involving the transfer of electrons. In electrolysis, it occurs at both electrodes, with oxidation happening at the anode and reduction at the cathode.

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Redox reaction

A specialized reaction where one substance loses electrons (oxidation) and another gains electrons (reduction) simultaneously.

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Test for water using anhydrous cobalt(II) chloride

A chemical test using anhydrous cobalt(II) chloride that turns from blue to pink when water is present.

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Test for water using anhydrous copper(II) sulfate

A chemical test using anhydrous copper(II) sulfate that turns from white to blue when water is present.

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Purity test of water

A method used to assess the purity of water by measuring the temperature at which it freezes (melting point) or boils (boiling point). Very pure water has a very specific melting and boiling point.

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Why distilled water is used in chemistry

Distilled water is free from salts and other impurities that might affect chemical reactions.

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Beneficial substance in water: Dissolved oxygen

Dissolved oxygen provides aquatic life with the oxygen they need to breathe.

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Beneficial substance in water: Metal compounds

Some metal compounds, like calcium and magnesium, are crucial for the growth and health of plants and animals.

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Harmful substance in water: Toxic metal compounds

Some metal compounds, such as mercury or lead, can be poisonous to living organisms.

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Harmful substance in water: Sewage

Sewage contains bacteria and viruses that can cause diseases.

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Harmful substance in water: Nitrates and phosphates

Nitrates and phosphates, often from fertilizers and detergents, contribute to the overgrowth of algae in water, leading to oxygen depletion and harm to other aquatic life.

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Treatment of water

The process of treating drinking water involves removing solids through sedimentation and filtration, removing tastes and odors using carbon, and killing microbes using chlorine.

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What is the mole and Avogadro's constant?

The mole (mol) is the SI unit for the amount of substance. One mole contains 6.02 x 10^23 particles (atoms, ions, molecules). This number is known as Avogadro's constant.

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How are mass, moles, and molar mass related?

The relationship between mass, amount of substance (moles), and molar mass is given by: amount of substance (mol) = mass (g) / molar mass (g/mol)

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What is molar mass?

Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol).

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What is molar gas volume?

The molar gas volume is the volume occupied by one mole of any gas at room temperature and pressure (r.t.p.). At r.t.p., the molar gas volume is 24 dm3.

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What is concentration?

Concentration is the amount of solute dissolved in a given volume of solution. It can be expressed in g/dm3 (grams per cubic decimeter) or mol/dm3 (moles per cubic decimeter).

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What is stoichiometry?

Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions.

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What is a limiting reactant?

A limiting reactant is the reactant that is completely consumed in a chemical reaction. It limits the amount of product that can be formed.

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What is titration?

Titration is a technique used to determine the concentration of a solution by reacting it with a solution of known concentration.

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What is an empirical formula?

An empirical formula shows the simplest whole-number ratio of atoms in a compound.

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What is a molecular formula?

A molecular formula shows the actual number of atoms of each element in a molecule.

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Reactivity Series and Metal Extraction

Metals that are easily obtained from their ores are located higher in the reactivity series. These metals are more reactive and readily lose electrons, making it easier to extract them from their compounds.

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Iron Extraction: Hematite

Hematite (Fe2O3) is the main ore used in the extraction of iron. The process takes place in a blast furnace, where iron oxide is reduced to iron using carbon as a reducing agent.

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Coke Burning in the Blast Furnace

Coke, a form of carbon, is burned in the blast furnace to provide heat and produce carbon dioxide (CO2).

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Carbon Dioxide Reduction in the Blast Furnace

Carbon dioxide reacts with excess carbon in the blast furnace to form carbon monoxide (CO).

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Iron Oxide Reduction in the Blast Furnace

Carbon monoxide acts as a reducing agent, reacting with iron(III) oxide (Fe2O3) to produce molten iron and carbon dioxide.

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Limestone Decomposition in the Blast Furnace

Limestone (CaCO3) decomposes into calcium oxide (CaO) and carbon dioxide in the blast furnace.

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Slag Formation in the Blast Furnace

Calcium oxide reacts with silica impurities in the ore to form slag (calcium silicate, CaSiO3). This molten slag is less dense than iron and floats on top, making it easier to remove.

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Aluminium Extraction: Bauxite and Electrolysis

Alumina (Al2O3) is the main ore of aluminium and is purified from bauxite. Electrolysis is then used to extract aluminium from the purified alumina.

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Role of Cryolite in Aluminium Extraction

Cryolite (Na3AlF6) is added to the molten alumina to lower the melting point, making the electrolysis process more efficient.

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Carbon Anodes in Aluminium Extraction

Carbon anodes are used in the electrolysis process. They are gradually consumed as they react with oxygen ions during electrolysis and need to be replaced regularly.

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Study Notes

Syllabus Overview

  • The syllabus is for IGCSE Chemistry (0620)
  • Exams are available in 2023, 2024, and 2025
  • Exams are offered in the June and November series
  • Exams are also available in the March series in India only

Aims

  • Enable students to acquire scientific knowledge and understanding of scientific theories and practice
  • Develop experimental skills, including handling variables and working safely
  • Use scientific data and evidence to solve problems and discuss limitations of scientific methods
  • Communicate effectively, using scientific terminology, notation, and conventions
  • Understand that scientific knowledge can benefit people and the environment
  • Enjoy science and develop an informed interest in scientific matters

Content Overview

  • States of matter
  • Atoms, elements, and compounds
  • Stoichiometry
  • Electrochemistry
  • Chemical energetics
  • Chemical reactions
  • Acids, bases, and salts
  • The Periodic Table
  • Metals
  • Chemistry of the environment
  • Organic chemistry
  • Experimental techniques and chemical analysis

Assessment Overview

  • All candidates take three papers.
  • Core candidates take Paper 1 (Multiple Choice), Paper 3 (Theory) and either Paper 5 (Practical Test) or Paper 6 (Alternative to Practical)
  • Extended candidates take Paper 2 (Multiple Choice), Paper 4 (Theory) and either Paper 5 or Paper 6

Assessment Objectives

  • AO1: Knowledge with understanding (50%)
  • AO2: Handling information and problem-solving (30%)
  • AO3: Experimental skills and investigations (20%)

Mathematical Requirements

  • Calculations may be used in all parts of the examination.
  • Including operations with numbers, decimals, fractions, percentages, ratios, standard forms, etc.
  • Algebraic manipulation and solving simple equations.
  • Using graphs and charts (interpolation and extrapolation for example.)
  • Calculating gradients and intercepts of lines on graphs.

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CIE Chemistry Syllabus Y11 PDF

Description

Test your understanding of key chemistry concepts related to exothermic and endothermic reactions, activation energy, and electrolysis processes. This quiz covers important principles and experimental outcomes relevant to the study of chemical reactions. Challenge yourself with questions about bond energies and the products of various electrolysis reactions.

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