Chapter 8

Question 1

Why are s2 metals so reactive? ( Group 2 )

Answer 1

Loss of 2 electrons from the atom produces a 2+ ion with noble gas electronic configuration.

Question 2

How do s2 metals form ionic compounds ?

Answer 2

Through loss of their s2 electrons in redox reactions, forming 2+ ions

Question 3

How do Group 2 metals react with water ?

Answer 3

They react with water to form alkaline hydroxides + hydrogen - general formula m(OH)2.
The metal is oxidised and Hydrogen is reduced

Question 4

How do Group 2 metal oxides react with water ?

Answer 4

Only produce metal hydroxide

Question 5

How do Group 2 metals react with oxygen ?

Answer 5

They react with oxygen to form metal oxides with general formula MO. Metal is oxidised, Oxygen is reduced

Question 6

How do Group 2 metals react with dilute acids?

Answer 6

They react with dilute acids to form a salt + hydrogen.
Metal is oxidised and Hydrogen is reduced

Question 7

What happens to the reactions with water, oxygen and dilute acids as you go down Group 2 ?

Answer 7

The reaction becomes more vigorous as reactivity increases

Question 8

Can you explain the trend in reactivity in terms of the first and second ionisation energies of Group 2 elements down the group?

Answer 8

Reactivity increases down Group 2 - s2 electrons are lost more easily ( less energy required )
Reactivity is reflected in ionisation energy, which decreases down the group.
The atomic radius increases and the outer electrons are more shielded, and so bonding electrons are less strongly attracted to the nucleus.
The atomic radius increases and there are more filled energy levels between the nucleus and the outer electron, and more shielding means lower I.E.

Question 9

What is produced when Group 2 oxides react with water ?

Answer 9

Hydroxide ( precipitate usually )

Question 10

Can group 2 hydroxides dissolve in water ?

Answer 10

If there is lots of water, then the hydroxides will dissolve, but Group 2 hydroxides are only slightly soluble in water. This means that they will be precipitated from solution if concentrations of the metal and OH- ions are high.

Question 11

Why are the Group 2 hydroxides produced referred to as alkali hydroxides ?

Answer 11

They are soluble bases that produce OH- ions in water

Question 12

What does the pH of the Group 2 hydroxides depend on ?

Answer 12

pH depends on how much OH- in in solution. Higher pH = more OH- ions.

Question 13

What happens to the strength, solubility and alkalinity of bases ( Group 2 ) as you go down the group ?

Answer 13

Strength increases as you down the group
Solubility increases as you go down the group
More soluble = more OH- ions = more alkaline ( more concentrated solution )

Question 14

What is the trend in solubility of Group 2 hydroxides ?

Answer 14

The solubility of the hydroxides increases down the group.
More concentrated solutions are more alkaline

Question 15

Describe uses of some Group 2 compounds as bases, including equations ( eg Ca(OH)2 )

Answer 15

Oxides, carbonates and hydroxides are bases. Group 2 bases have uses related to the fact that they can neutralise acids.
CaO + HCl →CaCl2 + H20
Ca(OH)2 + H2SO4 →CaSO4 + 2H20
CaCO3 + 2HNO3 →Ca(NO3)2 + H20 + CO2

hydroxide eg Ca(OH)2 is used in agriculture - added to fields by farmers to raise the pH of acid soil :
Ca(OH)2(s) + 2H+(aq) →Ca2+(aq) + 2H2O(l)

Question 16

Describe uses of some Group 2 compounds as bases, including equations, for example Mg(OH)2 and CaCO3 as ‘antacids’ in treating indigestion

Answer 16

Group 2 bases are used to treat acid indigestion (antacid).
Mainly magnesium hydroxide and calcium carbonate are used.
Stomach acid is mainly HCl(aq).
Mg(OH)2 is used as a suspension in water because the solubility of magnesium hydroxide is low.

Mg(OH)2 + 2HCl(aq) → MgCl2(aq) + 2H2O(l)
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

Question 17

Explain the existence of halogens as diatomic molecules

Answer 17

Each halogen is short of one electron to complete its octet and hence, has a strong tendency to share its unpaired electron with another atom of the same halogen to form diatomic molecules.

Question 18

What colour and state are F, Cl, Br and I at room temp ?

Answer 18

F = yellow gas
Cl = green gas
Br = dark red brown liquid
I = dark grey solid that turns purple after heating

Question 19

Explain the trend in the boiling points of Cl2, Br2 and I2, in terms of induced dipole–dipole interactions (London forces)?

Answer 19

Boiling / melting point increases going down the group
More electrons
Greater fluctuations in electronegativity
More / greater induced dipoles present
Greater London forces between molecules
More energy required to break London forces

Question 20

How do halogens form a 1- ions ?

Answer 20

the initial outer shell s2p5 electron configuration and the gaining of one electron in many redox reactions

Question 21

When are ionic and covalent compounds produced with halogens ?

Answer 21

Halogens give ionic compounds with metals (NaCl) but covalent compounds with non-metals (NCl3).

Question 22

Explain the trend in reactivity of the halogens Cl2, Br2, and I2, illustrated by reaction with other halide ions?

Answer 22

A more reactive halogen will displace the less reactive halogen in solution. ( displacement reactions )
Halide ions are oxidised to the elemental halogen and the halogen is reduced to the halide ion.
In interhalogen compounds the more reactive halogen will be in the -1 oxidation state (the other will be in a positive oxidation state).

Question 23

Are the halogens soluble in water and why ?

Answer 23

They are poorly soluble in water. There is little attraction between halogen molecules and water molecules. The inter molecular bonding between polar heads in water are too strong to be broken

Question 24

What colours are chlorine, bromine and iodine in water ?

Answer 24

Chlorine = pale green
Bromine = orange
Iodine = brown ( iodine ions are colourless )

Question 25

Are the halogens soluble in non polar, organic solvents ( eg cyclohexane ) and why ?

Answer 25

They are quite soluble because the intermolecular forces can form between the halogen molecules and the solvent. Due to their greater solubility, solutions of the halogens in non-polar solvents are much
darker than in water

Question 26

What colours are chlorine, bromine and iodine in organic solvents ?

Answer 26

Chlorine = pale green
Bromine = orange
Iodine = violet ( iodine ions are colourless )

Question 27

Explain the trend in reactivity from the decreasing ease of forming 1– ions, in terms of attraction, atomic radius and electron shielding?

Answer 27

Increasing atomic radius
Increased shielding from inner shells
Less nuclear attraction to capture an electron from another species
Reactivity decreases down the group

Question 28

Why are the halogens described as powerful oxidising agents ?

Answer 28

Because they are electron acceptors

Question 29

Put F2, Br2, I2 and Cl2 in order of increasing oxidising power

Answer 29

F2 > Cl2 > Br2 > I2

Question 30

Put F2, Br2, I2 and Cl2 in order of increasing reducing power

Answer 30

I2 > Br2 > Cl2 > F2

Question 31

Explain the term disproportionation, illustrated by the reaction of chlorine with water as used in water purification?

Answer 31

oxidation and reduction of the same element
Cl2 (g) + H2O (l)—-> HClO(aq) + HCL(aq)

Question 32

Explain the term disproportionation as oxidation and reduction of the same element, illustrated by the reaction of chlorine with cold, dilute aqueous sodium hydroxide, as used to form bleach?

Answer 32

Cl₂ (g) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H₂O (l)

Question 33

List and describe the benefits of chlorine use in water treatment contrasted with associated risks?

Answer 33

Pros : without chlorine in our water, we would be at risk of diseases such as typhoid and cholera.
Cons : Chlorine is a toxic gas.
Chlorine will react with methane in water (along with other organic hydrocarbons). Methane is formed by decaying vegetation.
The result of these reactions are chlorinated hydrocarbons, which are suspected carcinogens

Question 34

How to test for halide ions ?

Answer 34

Add silver nitrate to sample
Observe colour of precipitate

Question 35

What happens in the reaction between aq silver ions ( in the form of silver nitrate ) and aqueous Cl - ions ?

Answer 35

White precipitate forms
Ag+ (aq) + Cl-(aq) 🡪AgCl(s) (white precipitate)

Question 36

What happens in the reaction between aq silver ions ( in the form of silver nitrate ) and aqueous Br - ions ?

Answer 36

Cream precipitate forms
Ag+ (aq) + Br-(aq) 🡪AgBr(s) (cream precipitate)

Question 37

What happens in the reaction between aq silver ions ( in the form of silver nitrate ) and aqueous I - ions ?

Answer 37

Yellow precipitate forms
Ag+ (aq) + I-(aq) 🡪 AgI(s) (yellow precipitate)

Question 38

How do you distinguish between the silver halide precipitates ( of chlorine, bromine and iodine )formed after adding silver nitrate to the samples ?

Answer 38

Add aqueous ammonia solution

Dilute ammonia solution dissolves the white chloride precipitate but no others.
Concentrated ammonia dissolves the cream bromide and white chloride.
The yellow iodide precipitate does not dissolve in any ammonia solutions.

Question 39

What colour are halide, carbonate, sulphate and ammonium ions in solution ?

Answer 39

Colourless

Question 40

How to test for carbonate ions

Answer 40

Add acid ( nitric acid ) to produce a salt, water and carbon dioxide gas. The CO2 gas shows the presence of carbonate ions

Question 41

How to test for sulphate ions

Answer 41

Add barium ions ( Ba2+ ) in the form of Barium nitrate to sample. White precipitate is formed and CO2 gas. Barium sulphate is insoluble in water ( precipitate )

Question 42

How to test for ammonium ions

Answer 42

Hear sample with warm aq sodium hydroxide to form ammonia gas (NH3). Ammonia is alkaline so can be tested - turns damp litmus paper blue as ammonia dissolves in water.

Question 43

In what order should carbonates ions, sulphate ions and halide ions be tested ?

Answer 43

1) Carbonate
2) Sulphate
3) Halide

Question 44

Why should you carry out ion tests in a specific order ?

Answer 44

The first test is unequivocal and is not affected by any sulphate or halide ions present.
The halide test is carried out last because if there is any CO32- and SO42- present, precipitates of Ag2CO3 and Ag2SO4 would be formed – so these ions need to be removed in the first two tests).
If you plan to test for sulphate and halide ions you must make sure that these are not
part of the reagents used for the tests.
So for the carbonate test, the acid must not be hydrochloric acid or sulphuric (VI) acid.
So use nitric (V) acid for the carbonate test. Similarly, you should not use BaCl2 for the sulphate test as this will introduce Cl- ions that will spoil the halide test.
So use barium nitrate solution for the sulphate test.
After the sulphate test, the solution may need to be filtered before doing the halide test. This will make seeing any further precipitate straightforward.