Redox

Question 1

Reduction is what?

Answer 1

Loss of oxygen, gain of electrons or gaining hydrogen.

Question 2

Oxidation is what?

Answer 2

Addition of oxygen, loss of electrons or removal of hydrogen.

Question 3

What is disproportionation?

Answer 3

It is where on reactant (species) is simultaneously oxidised and reduced to form two products (one oxidised and one reduced).

Question 4

What is a reducing agent?

Answer 4

A reducing agent is a species that causes reduction in something else but it itself is oxidised. Eg: reactive metals.

Question 5

What is an oxidising agent?

Answer 5

Oxidising agents are species that cause oxidation in something else but it itself is reduced (becomes negative). Eg: Halogens.

Question 6

What happens to the halogens ability as oxidising agents as we go down group 7?

Answer 6

Their ability reduces, so chlorine is a better oxidising agent than iodine.

Question 7

It’s not always easy to see if something has been ox/red so we use what to help us?

Answer 7

Oxidation numbers.

Question 8

Oxidation numbers can be thought of as what?

Answer 8

The combining power of a species compared to oxygen.

Question 9

If an oxidation number goes up what has happened to that species?

Answer 9

It has been oxidised.

Question 10

If an oxidation number of a species goes down what has happened?

Answer 10

The species has been reduced.

Question 11

The oxidation number for all uncombined elements is…

Answer 11

…zero.

Question 12

In ions of just one atom the oxidation for that element is…

Answer 12

…the charge on the ion.

Question 13

The sum of oxidation numbers in a neutral compound is…

Answer 13

…zero.

Question 14

The sum of oxidation numbers for an ion is the…

Answer 14

…charge on the ion.

Question 15

Some elements have what kind of oxidation numbers in all compounds?

Answer 15

Fixed oxidation numbers.

Question 16

Metals with a fixed +1 oxidation numbers:

Answer 16

Group 1 metals. Eg: Li, Na, K

Question 17

Metals with a fixed +2 oxidation numbers:

Answer 17

Group 2 metals. Eg: Mg, Ca, Ba

Question 18

Metals with a fixed +3 oxidation number:

Answer 18

Aluminium.

Question 19

Non-metals with a fixed +1 oxidation number:

Answer 19

Hydrogen (except in metal hydrides, -1).

Question 20

Non-metals with a fixed -1 oxidation number:

Answer 20

Fluorine, chlorine (except in compounds with oxygen or fluorine).

Question 21

What is the fixed oxidation number of oxygen?

Answer 21

-2, except in peroxides, -1, and in compounds with fluorine.

Question 22

Steps for balancing redox equations:

Answer 22

1) Work out what’s ox/red.
2) Write a 1/2 equation to show electrons lost/gained.
3) Balance H with H+ and O with H2O if needed.
4) Make sure electron change is the same.
5) Add together.