Chemistry redox

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  • Created by: I.m
  • Created on: 24-12-12 21:21
In redox reactions how are each compounds treated in terms of charge?
Each compound is treated as though it were ionic, no matter what type of bonding is present.
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What is oxidation number?
The oxidation number tells us how many electrons are used when an element is bonded to other atoms in a compound.
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What are the three rules when working out oxidation states/numbers?
A. All elements have oxidation state = 0. B. the oxidation state of any neutral compound add up to zero. C. the oxidation states of any ion add up to the charge on that ion.
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Name the guidelines that you must follow when working out oxidation states/numbers?
Hydrogen is nearly always +1 (except with metals when = -1. Only metal=NaH). Oxygen is nearly always -2 (except in peroxides or with F when = -1. H₂O₂). Chlorine is nearly always -1 (except with O or F where it has positive values).
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What must the unknown oxidation number of an element be given as?
When we calculate an unknown oxidation number, we must always give the answer for a single element. E.g what is the oxidation state of nitrogen in N₂O₄? O = -2 so -2 x 4 = -8 so N₂= +8 so each nitrogen = +4.
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What do Roman numerals show in oxidation states?
If an element can exist in more than one possible oxidation state a Roman numeral is used to indicate the oxidation state of the element.
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What kind of elements use Roman numerals in their oxidation states?
Transition elements. These elements can form ions with different oxidation numbers. A Roman numeral is used to indicate the oxidation state of the transition element.
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Give example of oxidation states in some transition elements.
FeCl₂ = Iron (II) chloride, oxidation number = Fe+2. FeCl₃ = Iron (III) chloride, oxidation number = Fe+3. CuO = Copper (I) oxide, oxidation number = Cu+1. Cu₂O = Copper (II) oxide, oxidation number = Cu+2. MnO₄- = manganite (VII)ion, oxidation nu
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What are oxyanions and how does the name indicate what element they contain? Give examples.
Oxyanions are negative ions that contain oxygen (as indicated by the ending –‘ate’). E.g SO₄²-, CO₃²- and NO₃-
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What is oxidation?
Gain of oxygen. Loss of electrons. When the oxidation number increase.
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What is reduction?
Loss of oxygen. Gain of electrons. When oxidisation number decreases.
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In what type of reaction does oxidation and reduction take place and why?
Oxidation and reduction always take place together in a redox reaction. This is because one process is always accompanied by the other.
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In a redox reaction, what does the species that is reduced act as?
In a redox reaction, the species that is reduced acts as an oxidising agent.
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In a redox reaction, what does the species that is oxidised act as?
Similarly, the species that is oxidised act as a reducing agent.
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How are redox equations written?
As redox reaction consist of two half-reactions (one oxidation and one reduction), these half-reactions can be written as half-equations (one for oxidation and the other for reduction).
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In half-equations which side do you show oxidation and reduction?
Reduction = left. Oxidation = right.
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Are metals usually oxidised or reduced?
Metals e.g. Na, K, Mg etc. tend to undergo oxidation. They lose electrons forming positive ions. Their oxidation number increases.
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Are non-metals usually oxidised or reduced?
Non-metals e.g. O₂,Cl₂ tend to undergo reduction. They gain electron forming negative ions. Their oxidation number decreases.
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When reactive metals react with acids, what do they form?
Reactive metals react with acids to form salts and hydrogen gas.
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What type of reaction is a metal with an acid?
Redox reaction.
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What observations are made when magnesium reacts with hydrochloric acid?
Effervescence and magnesium solid dissolves.
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What gas is given off when magnesium and hydrochloric acid react?
Hydrogen.
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Write the balanced equation for the reaction of magnesium with hydrochloric acid?
Mg +2HCl = MgCl₂ +H₂.
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Magnesium reacts with hydrochloric acid. The balanced equation is Mg +2HCl = MgCl₂ +H₂. What is oxidised and what is reduced in this reaction?
Oxidised = magnesium (lost 2e-) 0----+2. Reduced = hydrogen (gained e-) +1----0.
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Write the balanced equation for the reaction between magnesium and sulphuric acid.
Mg + H₂SO₄ = MgSO₄ + H₂.
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Magnesium reacts with sulphuric acid. The balanced equation is Mg + H₂SO₄ = MgSO₄ + H₂. What is oxidised and what is reduced in this reaction?
Oxidised = magnesium (lost 2e-) 0---+2. Reduced = hydrogen (gained e-) +1----0.
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Other cards in this set

Card 2

Front

What is oxidation number?

Back

The oxidation number tells us how many electrons are used when an element is bonded to other atoms in a compound.

Card 3

Front

What are the three rules when working out oxidation states/numbers?

Back

Preview of the front of card 3

Card 4

Front

Name the guidelines that you must follow when working out oxidation states/numbers?

Back

Preview of the front of card 4

Card 5

Front

What must the unknown oxidation number of an element be given as?

Back

Preview of the front of card 5
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