Redox Reactions

Question 1

What is the reaction for magnesium reacting with oxygen?

Answer 1

Mg (s) + 0.5O2 (g) -> MgO (s)

Question 2

What is the structure of magnesium oxide?

Answer 2

In has a giant structure consisting of magnesium ions Mg2+ and oxide ione O2-

Question 3

How is magnesium oxide formed regarding ion transfer?

Answer 3

Two electrons are transferred from the outer shell of the magnesium whicb gives a stable noble gas configuration to form Mg2+. The oxygen atom gains the two electrons to form O2-, which also has a stable noble gas configuration

Question 4

What are the two half equations for the formation of magnesium oxide?

Answer 4

• Mg -> Mg2+ + 2e-

* 0.5O2 + 2e- -> O2-

Question 5

How can you get the full equation from half equations?

Answer 5

You add them together

Question 6

Whatbis oxidation?

Answer 6

The loss of electrons

Question 7

What is reduction?

Answer 7

The gain of electrons

Question 8

What are redox reactions?

Answer 8

When one reactant is oxidised and the other is reduced

Question 9

What does OIL RIG stand for?

Answer 9

Oxidation is loss

Reduction is gain

Question 10

What are oxidising agents?

Answer 10

The reactant that does the oxidising. They are electron acceptors and are themselves reduced

Question 11

What is the reducing agent?

Answer 11

The reactant that does the reducing. They are electron donors and are themseleves oxidies

Question 12

In this equation Na + 0.5Cl2 -> NaCl which reactants are oxidised and reduced and so which are the oxidising and reducing agents?

Answer 12

• Na: oxidised so is the reducing agent

* Cl2: reduced so is the oxidising agent

Question 13

What are the rules for constructing half equations?

Answer 13

1. Write down the formulae of the reactants and products
2. Balance any atoms that are not hydrogen or oxygen
3. Add H2O to balance oxygen atoms
4. Add H+ ions to balance hydrogen atoms
5. Balance charges by adding electrons
6. (Add state symbols)
7. Check equation by writing the oxidation numbers and number of electrons

Question 14

What are the rules for combining half equations?

Answer 14

1. Write down the two half equations
2. multiply if necessary to balance electrons
3. Add together the two half equations
4. Cancel e-, H20 and H+ where necessary
5. Check atoms and charges balance
6. Add state symbols

Question 15

In sodium chloride what is the oxidation state for sodium and chlorine?

Answer 15

Sodium has the oxidation state +1 and chlorine has the oxidation state -1

Question 16

What are the IUPAC rules for assigning oxidations states (oxidation numbers)

Answer 16

1) the oxidation state of a free (uncombined) element is always zero
2) for a simple monatomic ion the oxidation state is the charge on the ion
3) hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2 in most compounds. The exceptions are hydrogen in hydrides of active metals which has an oxidation state of -1 and oxygen which has an oxidation state of -1 in peroxides (e.g. H2O2)
4) the sum of the oxidation states of all atoms in a neutral molecule must be zero.
5) For ions the sum of the oxidation states of the constituent atoms must equal the charge on the ion

Question 17

How is the oxidation state of an element in a particular compound with more than one oxidation state shown?

Answer 17

By Roman numeral in brackets after the element in the chemical name. There is no space between the bracketed Roman numerals and the element is described:

E.g. iron(II) sulfate with iron having an oxidation state of +2

Question 18

What is an oxyanion?

Answer 18

It is made from atoms of two elements, one of which is oxygen

Question 19

Where is much less consistent in the use of variable oxidation states ( roman numerals)?

Answer 19

Non-metals e.g. CO is always called carbon monoxide rather than carbon(II) oxide

Question 20

What are oxyanions containing chlorine called?

Answer 20

Chlorates

Question 21

How can oxidation states be used to define oxidation and reduction?

Answer 21

• oxidation occurs when the oxidation state of an element in a reaction increases
• reduction occurs when the oxidation state of an element in a reaction decreases

Question 22

In the reaction between hydrogen and oxygen what happens with oxidation and reduction?

Answer 22

Hydrogen is oxidised because its oxidation state increases from 0 to +1, while oxygen is reduces because its oxidation state decreases from 0 to -2. To make the equation balanced, for one oxygen being reduced from 0 to -2, two hydrogens must be oxidised from 0 to +1 so it is H2O

Question 23

What are redox equations also called and what do they show?

Answer 23

They are also called ionic equations. They show what is oxidised and what is reduced in a redox reaction. They do not include ions that are unchanged and present before and after the reaction

Question 24

For redox reactions how do we work out the overall redox equation?

Answer 24

• By combining the oxidation and reduction half equations

* by seperating the full balanced equation into it’s ions and then removing the spectator ions

Question 25

What are the

Answer 25

J

Question 26

What are spectator ions?

Answer 26

Ions that do not take part in the reaction and qre the same on both sides of the equation