Acids and redox

Question 1

What is the oxidation number?

Answer 1

This is the total number of electrons it has donated or accepted to form an ion or to form part of a compound.

Question 2

What is the oxidation state of elements?

Answer 2

Uncombined elements are 0, they haven’t accepted or donated any electrons.
Elements bonded to identical atoms are also 0.
Simple monatomic ions is the same as its charge.

Question 3

What is the oxidation state of molecular ions?

Answer 3

Each of the constituent atoms has an oxidation number of its own and the sum of these equals the oxidation number, which is equal to the charge of the ion.

Question 4

What is the oxidation state of oxygen?

Answer 4

It is usually -2.
In peroxides (O2^2-), it is -1.
In molecular oxygen, it is 0.
In F2O it is +2.

Question 5

What is the oxidation state of hydrogen?

Answer 5

It is always +1.
Except in metal hydrides, where it is -1.
In molecular hydrogen it is 0.

Question 6

What is the oxidation state of fluorine?

Answer 6

It is always -1.

Question 7

What is oxidation?

Answer 7

A loss of electrons.
A gain of oxygen.
A loss of hydrogen.

Question 8

What is reduction?

Answer 8

A gain of electrons.
A loss of oxygen.
A gain of hydrogen.

Question 9

What is an oxidising agent?

Answer 9

It accepts electrons and gets reduced.

Question 10

What is a reducing agent?

Answer 10

It donates electrons and gets oxidised.

Question 11

How do oxidation numbers change in redox?

Answer 11

The oxidation number of an atom will increase by 1 for each electron lost.
The oxidation number will decrease by 1 for each electron gained.

Question 12

What is the trend for oxidation numbers?

Answer 12

When metals form compounds, they generally donate electrons to form positive ions - so they usually have positive oxidation numbers.
When non-metals form compounds, they generally gain electrons, so have negative oxidation numbers.

Question 13

What is the reaction of dilute acids with metals?

Answer 13

The metal atoms are oxidised, losing electrons to form positive metal ions (in salts).
The hydrogen ions in solution are reduced, gaining electrons and forming hydrogen molecules.

Question 14

What is disproportionation?

Answer 14

The reduction and oxidation of the same element.

Question 15

What are acids?

Answer 15

Proton donors.
When mixed with water, they release hydrogen ions. (Protons)

Question 16

What are bases?

Answer 16

Proton acceptors.
Bases remove hydrogen ions from an aqueous solution.
Metal oxides, metal hydroxides, metal carbonates, and ammonia.
They neutralise an acid to form a salt.

Question 17

What are alkalis?

Answer 17

Bases that are soluble in water.
They release OH- ions in solution.

Question 18

What are common acids?

Answer 18

HCl - hydrochloric acid
H2SO4 - sulfuric acid
HNO3 - nitric acid
CH3COOH - ethanoic acid

Question 19

What are common bases?

Answer 19

NaOH - sodium hydroxide
KOH - potassium hydroxide
NH3 - ammonia

Question 20

What is the strength of acids and bases?

Answer 20

Strength depends on whether the forwards or backwards reaction is more prevalent, and to what extent the acid or base is ionised in solution.

Question 21

What are strong acids and bases?

Answer 21

E.g., HCl, very little of the reverse reaction happens, so the acid completely dissociates in water, and all the H+ ions are released.
NaOH is a strong base. Most of the OH- ions are released.

Question 22

What are weak acids and bases?

Answer 22

The backwards reaction is favoured, so the acid only partially dissociates in water and only some H+ ions are released.
It is written as a reversible reaction.
Ethanoic acid is weak.
Ammonia is a weak base.

Question 23

What is a salt?

Answer 23

When hydrogen ions are replaced by metal ions or ammonium (NH4+) ions.

Question 24

What are examples of salts?

Answer 24

H2SO4 produces sulfates (SO42- ions).
HCl produces chlorides (Cl- ions).
HNO3 produces nitrates (NO3- ions)

Question 25

What are acid-base reactions?

Answer 25

Acid + base –> salt + water
The H+ ions released from the acid, and the OH- ions from the alkali combine to form water.

Question 26

What are acid-metal reactions?

Answer 26

Metal + acid –> salt + hydrogen

Question 27

What are acid-metal oxide reactions?

Answer 27

Metal oxide + acid –> salt + water

Question 28

What are acid-metal hydroxide reactions?

Answer 28

Metal hydroxide + acid –> salt + water

Question 29

What are acid-carbonate reactions?

Answer 29

Metal carbonate + acid –> salt + carbon dioxide + water

Question 30

What is a titration?

Answer 30

A technique used to accurately measure the volume of one solution that reacts exactly with another solution.
They can be used to find the concentration of a solution, identify unknown chemicals, find the purity of a substance.

Question 31

What are titration calculations of scaling?

Answer 31

The student dissolves 5.766 g of the amino acid in water and makes the solution up to
250.0 cm 3 in a volumetric flask.
* The student titrates this solution with 25.0 cm 3 of 0.150 mol dm−3 hydrochloric acid.
* 21.30 cm 3 of the amino acid solution were required for complete neutralisation of HCl.
Find moles of HCl
Multiply by 250/21.3 to find the scale and the moles of amino acid.

Question 32

What are titration calculations?

Answer 32

c1 x v1 = c2 x v2
Work out the amount in mol of the solute in the solution for which you know both the concentration and volume.
Use the equation to work out the amount of solute in the other solution.
Work out the unknown information about the solute in the other solution.