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Chemistry A Level AQA > 3.1.7- Oxidation, reduction and redox equations (PAPER 1) > Flashcards

3.1.7- Oxidation, reduction and redox equations (PAPER 1) Flashcards

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1
Q

What is oxidation? (o,e,h)

A

The gain of oxygen, the loss of electrons, the loss of hydrogen.

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2
Q

What is reduction? (o,e,h)

A

The loss of oxygen, the gain of electrons, the gain of hydrogen.

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3
Q

How to remember oxidation and reduction?

A

OILRIG
oxidation is loss of e- and H, reduction is gain of e- H

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4
Q

What is a redox reaction?

A

When one chemical gains electrons/ is reduced and another loses electrons/ is oxidised.

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5
Q

What is an oxidation state?

A

The number of electrons something needs to lose or gain to become neutral.

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6
Q

What is the oxidation state of uncombined elements/ diatomic molecules?

A

0 as they are already neutral.

Eg- Na, Fe, Br2, Cl2

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7
Q

What is the oxidation state of group 1 elements?

A

+1

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7
Q

What is the oxidation state of a monatomic ion? -ion made up of one single atom with charge.

Eg- K+, Al3+, Cl-

A

The same as the charge on the atom/ion.

Eg- K+ has an oxidation state of +1

Eg- Al3+ needs to gain 3 electrons to become neutral so oxidation state is +3

Eg- Cl- needs to lose 1 electron so its oxidation state is -1

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7
Q

What is the oxidation state of group 2 elements?

A

+2

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7
Q

What is the typical oxidation state of group 3 elements?

A

+3

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7
Q

What is the typical oxidation state for group 5 elements?

A

-3

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7
Q

What is the typical oxidation state for group 6 elements?

A

-2

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7
Q

What is the typical oxidation state for group 7 elements?

A

-1

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7
Q

How to know transition metal oxidation states? Eg- iron(iii) oxide

A

The roman numeral next to the metal

Eg- iron (iii) oxide
iron = +3 oxidation state

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7
Q

What is the oxidation state for hydrogen+ anomaly?

A

+1 Eg- HF

UNLESS in hydrides, then it is -1 Eg- NaH

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7
Q

What is the oxidation state for chlorine + anomaly?

A

-1 Eg- KCl

UNLESS in a compound with F and O, it would be + Eg ClF3 Cl= =3

7
Q

What is the oxidation state for fluorine + anomaly?

A

-1 Eg- KF

7
Q

What is the oxidation state for oxygen + anomaly?

A

-2 Eg- Li2O

UNLESS in peroxides Eg- H202 O= -1
UNLESS in F20 O= +2

7
Q

How to work out oxidation state of a compound?

A

All oxidation states must add to give overall charge of compound= eg 0, -1, -2

7
Q

What is the oxidation state of N in NH4 + ?

A

H= +1 x 4 = +4
how to get from +4 to +1?

N= -3

7
Q

What is the oxidation state of Cr in Cr2O7 2- ?

A

O= -2 x 7 = -14
how to get from -14 to -2?
Cr2 = +12 so Cr = +6

7
Q

Difference between oxidation and reduction half equation?

A

In reduction half equations, the electrons appear on the left as they are being gained.

In oxidation half equations, the electrons appear on the right as they are being lost.

7
Q

What are the 5 steps to writing half equations?

A

1) Write what you know as an equation.
2) Balance for atoms (not O or H)
3) Balance for O by adding H2O
4) Balance for H by adding H+ ions
5) Balance charge by adding e- ON THE SAME SIDE AS THE + CHARGE

7
Q

Write the half equation for I- reacting to make I2

A

1) I- —-> I2
2) 2I- —–> I2
5) 2I- ——> I2 + 2e-

Iodide has been oxidised as electrons are on the right so have been lost.

ITS OXIDATION NUMBER INCREASES.

8
Q

Write the half equation for MnO4 - to Mn 2+

A

1) MnO4 - ——-> Mn2+
3) MnO4 - ——–> Mn2+ 4H20
4) MnO4- + 8H+ ———> Mn2+ + 4H2O (4H2 = 8H)
5) RHS is +2, LHS is +7
MnO4 - + 8H+ + 5e- ——–> Mn 2+ +4H2O

9
Q

What is the method for combining half equations?

A

1) Write out the 2 half equations
2) Multiply the equations so they both have the same number of e-
3) Add the 2 equations, cancel out the same e- on each side
4) Cancel out other species which appear on both sides of final equation

10
Q

Combine these 2 half equations:
Fe 3+ + 3e- —-> Fe
2 I- —–> I2 + 2e-

A

Fe 3+ + 3e- —-> Fe X2
2Fe 3+ + 6e- ——> 2Fe
2 I- —–> I2 + 2e- X3
6I- ——> 3I2 + 6e-

add the new equations=
2Fe 3+ + 6e- + 6I- —–> 2Fe + 3I2 + 6e-
cancel out
2Fe 3+ + 6I- ——-> 2Fe + 3I2

11
Q

How to recognise which is reducing and oxidising agent from 2 half equations?

A

Eg-

Fe—–> Fe2+ + 2e-
-electrons on right side= reactant is losing electrons, oxidation
MnO4- + 5e- + 8H+ —–> Mn 2+ + 4H2O
-electrons on left side= reactant is gaining electrons, reduction

Red——-ox
REDUCTION ON LEFT, OXIDATION ON RIGHT

12
Q

How to recognise which is reducing and oxidising agent from full equation?

A

Eg- 5Fe + 2MnO4- —–> 5Fe 2+ + 2Mn 2+ + 8H20

work out oxidation states
O state 5Fe= 0
O state 5Fe 2+ = +2
Fe OXIDISED

O state 2MnO4- Mn= +7
O state 2Mn 2+ Mn= +2
Mn REDUCED

12
Q

What is a reducing agent?

A

Causes something else to be reduced by donating electrons.

Is oxidised itself

13
Q

What is an oxidising agent?

A

Causes something else to be oxidised by accepting electrons.

Is reduced itself.

Chemistry A Level AQA (25 decks)

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