Starter quiz
- What is an ion and how is it formed?
- It is a charged particle formed by an atom gaining or losing proton.
- It is a neutral particle formed by an atom gaining or losing electrons.
- It is a charged particle formed by an atom gaining or losing electrons. ✓
- It is a neutral particle formed by an atom gaining or losing neutrons.
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- What does the law of conservation of mass state?
- Mass can be created and destroyed, allowing for new matter.
- Mass is always lost in a chemical reaction, reducing reactants.
- Mass is neither created nor destroyed in a chemical reaction. ✓
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- What is electrolysis and what is its purpose?
- It is a method of mixing substances to form a solution.
- It is a process that uses electric current to drive a chemical reaction. ✓
- It is a technique for measuring the mass of an element.
- It is the flow of electrons in a circuit.
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- What is an aqueous solution?
- It is a solution in which a substance is dissolved in acid.
- It is a solution in which a substance is dissolved in water. ✓
- It is a solution in which a substance is dissolved in alcohol.
- It is a substance in its liquid state.
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- What is the role of the anode in electrolysis?
- It is the negatively charged electrode where reduction occurs.
- It is the positively charged electrode where oxidation occurs. ✓
- It is where the electrolyte is added.
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- What is the role of the cathode in electrolysis?
- It is the negatively charged electrode where reduction occurs. ✓
- It is the positively charged electrode where oxidation occurs.
- It is where the electrolyte is added.
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Exit quiz
- Which ions compete to be discharged at the cathode?
- negative ions
- neutral ions
- positive ions ✓
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- Which ions compete to be discharged at the anode, and what determines their discharge?
- only negative ions compete; the more abundant ion is discharged
- positive and negative ions compete; the ion with the highest charge is discharge
- negative ions compete; the one with the lower reactivity is discharged ✓
- positive ions compete; the ion with the lower charge is discharged
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- What gas is commonly formed at the cathode during the electrolysis of sodium chloride solution, and why?
- chlorine, because it is produced at the cathode
- hydrogen, because sodium is more reactive than hydrogen ✓
- oxygen, because it is a common gas
- nitrogen, because it is the most abundant in the atmosphere
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- How can you test for the presence of hydrogen gas, and what is the expected result?
- it relights a glowing splint
- it turns lime water milky
- a litmus test; the paper turns red then bleaches white
- the squeaky pop test ✓
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- What determines whether hydrogen or a metal is produced at the cathode during electrolysis?
- the concentration of the electrolyte
- the reactivity of the metal compared to hydrogen ✓
- the temperature of the solution
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- What is the expected result when litmus paper is exposed to chlorine gas, and why?
- it bleaches it white because chlorine is a strong oxidising agent ✓
- there is no change because chlorine is inert
- it turns blue because chlorine is alkaline
- it turns red because chlorine is acidic ✓
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Multiple types of positive ions are in competition at the negative electrode (cathode).
- Multiple types of negative ions are in competition at the positive electrode (anode).
- There are rules for which substances are discharged at the anode and cathode.
- The gases produced during electrolysis can be collected and tested.
- Hydrogen may be formed at the cathode
Common misconception
Recognising the particles present in an aqueous solution is problematic. Understanding how an electric current flows through an electrolyte is confusing as ions, not electrons, are the charge carrier.
Ensure that students have a good understanding of key terms such as atom, ion, electron, solutions and reactivity before moving on to the electrolysis of aqueous solutions.
Keywords
Aqueous solution - formed when a substance is dissolved in water
Cathode - a negatively charged electrode, in an electrolysis cell, to which the anions are attracted
Anode - a positively charged electrode, in an electrolysis cell, to which the cations are attracted
Electrolyte - a liquid or solution that contains freely moving ions
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