Chemistry redox
3.5 / 5 based on 3 ratings
- 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.
1 of 26
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.
2 of 26
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.
3 of 26
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).
4 of 26
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.
5 of 26
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.
6 of 26
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.
7 of 26
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
8 of 26
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-
9 of 26
What is oxidation?
Gain of oxygen. Loss of electrons. When the oxidation number increase.
10 of 26
What is reduction?
Loss of oxygen. Gain of electrons. When oxidisation number decreases.
11 of 26
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.
12 of 26
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.
13 of 26
In a redox reaction, what does the species that is oxidised act as?
Similarly, the species that is oxidised act as a reducing agent.
14 of 26
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).
15 of 26
In half-equations which side do you show oxidation and reduction?
Reduction = left. Oxidation = right.
16 of 26
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.
17 of 26
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.
18 of 26
When reactive metals react with acids, what do they form?
Reactive metals react with acids to form salts and hydrogen gas.
19 of 26
What type of reaction is a metal with an acid?
Redox reaction.
20 of 26
What observations are made when magnesium reacts with hydrochloric acid?
Effervescence and magnesium solid dissolves.
21 of 26
What gas is given off when magnesium and hydrochloric acid react?
Hydrogen.
22 of 26
Write the balanced equation for the reaction of magnesium with hydrochloric acid?
Mg +2HCl = MgCl₂ +H₂.
23 of 26
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.
24 of 26
Write the balanced equation for the reaction between magnesium and sulphuric acid.
Mg + H₂SO₄ = MgSO₄ + H₂.
25 of 26
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.
26 of 26
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
Card 4
Front
Name the guidelines that you must follow when working out oxidation states/numbers?
Back
Card 5
Front
What must the unknown oxidation number of an element be given as?
Back
Related discussions on The Student Room
- chemistry a level »
- Tips for physical A level chemistry OCR A? »
- A level topic predictions?? Chemistry, biology, psychology »
- National 5 Chemistry »
- Redox Reactions »
- Chem alevel help »
- AS Chemistry Paper 1 2022 »
- a level redox question »
- Inorganic Chemistry (AQA) - A level »
- A level chemistry Redox help please. »
Similar Chemistry resources:
0.0 / 5
0.0 / 5
3.5 / 5 based on 3 ratings
0.0 / 5
0.0 / 5
4.0 / 5 based on 1 rating
2.0 / 5 based on 1 rating
0.0 / 5
0.0 / 5
4.0 / 5 based on 1 rating
Comments
No comments have yet been made