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iGCSE Chemistry: Electrolysis - core

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All the atoms in group 1 have 1 electron in their outer shell. What charge ions do they form?
+1
All the atoms in group 3 have 3 electron in their outer shell. What charge ions do they form?
+3
All the atoms in group 5 have 5 electron in their outer shell. What charge ions do they form?
-3
All the atoms in group 7 have 7 electron in their outer shell. What charge ions do they form?
-1
Describe, in terms of electrons, the formation of sodium chloride
An atom of sodium loses one electron. An atom of chlorine gains one electron
State the electron configuration of the fluoride ion
2,8
What is the formula of the calcium ion?
Ca²⁺
Zinc phosphide, Zn₃P₂ is an ionic compound. The formula of the zinc ion is Zn²⁺. Deduce the formula of the phosphide ion
P³⁻
Do ionic substances conduct electricity?
Not when solid, but they do when either molten or in solution
When can ionic substances conduct electricity?
When molten or dissolved
A substance is found not to conduct electricity even when molten. What type of bonding does the substance have?
Covalent
Explain what is meant by electric current
The rate of flow of charge particles (e.g. of electrons or ions)
Typically, so covalent substances conduct electricity?
No
(Triple only) Draw a diagram to show the bonding in a metal
(Triple only) Explain why metals are good conductors of electricity
Metals have delocalised electrons which are free to move
(Triple only) Explain why metals are malleable
Metals have layers of ions that can slide over each other
(Triple only) What does the word malleable mean?
able to be hammered or pressed into shape without breaking or cracking
(Triple only) Why do metals have high melting and boiling points?
There is a strong electrostatic attraction between a regular structure of positive metal ions and a sea of delocalised electrons
(Triple only) State whether covalent susbances conduct electricity, and explain why
There are no charged particles that are free to move
(Triple only) Why do covalent compounds (e.g H₂O) not conduct electricity?
There are no charged particles that are free to move
(Triple only) Explain whether solid ionic compounds conduct electricity
Solid ionic compounds cannot conduct electricity because the ions are not free to move
(Triple only) Why do ionic compounds conduct electricity only when molten or in solution?
When solid the ions are held in place. When molten or in solution the ions are free to move
(Triple only) What are negative ions called?
anions
(Triple only) What are positive ions called?
cations
(Triple only) During the electrolysis of water, oxygen gas is given off. The formation of this gas can be represented by the ionic equation: ....OH⁻ → ....H₂O + ....O₂ + ....e⁻
4OH⁻ → 2H₂O + O₂ + 4e⁻
(Triple only) Explain what is meant by electrolysis
The breakdown of a substance using electricity
(Triple only) How could you determine if a liquid is an electrolyte?
Put it in a circuit including a bulb. If the bulb lights then the liquid is an electrolyte
(Triple only) In the electrolysis of molten aluminium oxide, write the name and formula of the particles which move to the negative electrode
aluminium ions (Al³⁺)
(Triple only) In the electrolysis of molten aluminium oxide, write the name and formula of the particles which move to the positive electrode
oxide ions (O²⁻)
(Triple only) Name the product formed at the anode during the electrolysis of molten copper chloride
chlorine
(Triple only) The overall equation for the decomposition of water is: 2H₂O(l) → 2H₂(g) + O₂(g) Use this equation to explain why the volume of hydrogen collected should be twice that of the volume of oxygen.
The number of moles of H₂ are twice that of oxygen
(Triple only) What is the name for the negative electrode?
cathode
(Triple only) What is the name for the positive electrode?
anode
(Triple only) What type of reaction takes place at the anode?
oxidation
(Triple only) What type of reaction takes place at the cathode?
reduction
(Triple only) In terms of electrons, what is oxidation?
Oxidation is the loss of electrons
(Triple only) In terms of electrons, what is reduction?
Reduction is the gain of electrons
(Triple only) The chemical equations for the two reactions that occur during the extraction of aluminium are A: Al³⁺ + 3e¯ → Al and B: C + O₂ → CO₂. State and explain which species in the reactions are oxidation or reduction
A: Al³⁺ is reduced because it gains electrons. B: C is oxidised because it gains oxygen
(Triple only) What is the formula of aluminium oxide?
Al₂O₃
(Triple only) When chlorine gas is bubbled into an aqueous solution of potassium iodide, the colourless solution turns brown. Complete the following ionic equation: Cl₂(g)+ ___I⁻(aq) → 2Cl⁻(aq) + ___(aq)
Cl₂(g) + 2I⁻(aq) → 2Cl⁻(aq) + I₂(aq)
(Triple only) Write ionic half-equations for the reactions at the electrodes in aluminium extraction
Al³⁺ + 3e⁻ → Al and 2O²⁻ → O₂ + 4e⁻
(Triple only) Draw an electrolysis cell used to investigate the electrolysis of aqueous solutions
An experiment investigates which of metals X and Z is more reactive. The result is X + ZSO₄ → X + ZSO₄. Which metal is more reactive?
Z. There is no reaction.
An experiment investigates which of metals X and Z is more reactive. The result is X + ZSO₄ → XSO₄ + Z. Which metal is more reactive?
X. This is a displacement reaction.
Explain in 2 different ways why rusting is described as an oxidation reaction
iron gains oxygen / iron loses electrons
If a substance gains oxygen in a reaction how is the process described?
Oxidation
If a substance loses oxygen in a reaction how is the process described?
Reduction
In halogen displacement reactions, electrons are transferred from one atom to another. How are these reactions classified?
REDOX
Is the production of iron from iron ore oxidation or reduction?
Reduction
State the meaning of the term oxidising agent
A substance that gives oxygen or removes electrons (it is itself reduced)
State the meaning of the term redox
A reaction involving both reduction and oxidation
State the meaning of the term reducing agent
A substance that takes oxygen or gives electrons (it is itself oxidised)
What is it called when a metal reacts with oxygen in the air to form an oxide layer?
Oxidation
(Triple only) In the earth's crust, in what form are most metals usually found?
As an ore: a compound containing the metal
(Triple only) What do you call a rock which metal can be extracted from?
ore
(Triple only) What is an ore?
A rock (compound) which metal can be extracted from.
(Triple only) What type of metals might be found in the Earth's crust as uncombined elements (i.e. not as compounds)?
Unreactive metals
(Triple only) For the extraction of which metals is electrolysis used, and which use the displacement method?
Metals above carbon in the reactivity series are extracted by electrolysis. For those below, displacement is used.
(Triple only) Name the process used to extract aluminium
Electrolysis
(Triple only) What are the two main methods of extracting metals?
Electrolysis and displacement
(Triple only) Why is aluminium not extracted using a displacement reaction with carbon?
Aluminium is more reactive than carbon
(Triple only) Carbon is more reactive than tin. What method should be used to extract tin from its ore?
Displacement with carbon
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