Inorganic Chemistry

How does atomic radius change down Group 2, and why?

Atomic radius increases down Group 2 because the number of electron energy levels increases.

How does melting point change down Group 2, and why?

Melting point changes down Group 2 because the ions get bigger, and the strength of attraction between the sea of delocalised electrons and metal ions changes.

How does ionisation energy change down Group 2, and why?

Ionisation energy decreases down Group 2 because the outermost electrons are held increasingly further away from the nucleus, so less energy is needed to overcome the attraction between the nucleus and the outer electrons.

Why does ionisation energy decrease down Group 2?

The outer electron is in a higher energy level, shielding increases, and the attraction between the outer electron and the nucleus becomes weaker.

What is the equation and observation when magnesium reacts with cold water?

Mg(s) + 2H₂O(l) → Mg(OH)₂(s) + H₂(g)

Hydrogen bubbles start to appear.

What is the equation and observation when calcium reacts with water?

Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

The reaction is more vigorous than magnesium, bubbles form at a faster rate, and the mixture heats up.

What is the equation and observation when magnesium reacts with steam?

Mg(s) + H₂O(g) → MgO(s) + H₂(g)

Magnesium reacts vigorously with steam, producing a bright white flame and a white powder.

How does the solubility of Group 2 hydroxides and sulfates change down the group?

The solubility of Group 2 hydroxides increases down the group, while the solubility of Group 2 sulfates decreases down the group.

Why is barium sulfate used in X-rays?

Barium sulfate absorbs X-rays. The patient is given a barium meal consisting of a paste of barium sulfate, which fills the digestive system. The X-rays are absorbed, allowing an image of the organs to be obtained. Barium sulfate is toxic but safe to ingest because it is insoluble and cannot dissolve and pass through cell membranes into body tissues.

What is magnesium hydroxide used for, and why?

Magnesium hydroxide is used in indigestion tablets because it is alkaline and neutralises excess stomach acid.

Why is barium sulfate safe to ingest despite being toxic?

Barium sulfate is insoluble, so it cannot dissolve and pass through cell membranes into body tissues.

What is calcium hydroxide used for in farming, and why?

Calcium hydroxide is used to neutralise acidic soils because it is alkaline.

How do you test for sulfate ions?

Add barium chloride solution. A white precipitate forms.

What is the ionic equation for the sulfate ion test?

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

Acidify the sample with dilute hydrochloric acid first to remove interfering ions such as carbonate ions.

How is magnesium used to extract titanium from titanium chloride?

2Mg(s) + TiCl₄(l) → Ti(s) + 2MgCl₂(l)

Magnesium reduces titanium ions to titanium.

Why is excess solid added when preparing strontium hydroxide solution?

To make sure that as much solid as possible dissolves, producing a saturated solution.

Why must undissolved strontium hydroxide be removed before titration?

It would react with the acid during the titration.

Why is the flask stoppered after filtration?

To prevent reaction with carbon dioxide in the air and to prevent evaporation of water.

What is the equation for magnesium reacting with hydrochloric acid?

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Describe the structure and bonding in magnesium.

Magnesium has a giant metallic lattice with electrostatic attraction between delocalised electrons and Mg²⁺ ions.

Which silver halide dissolves in dilute ammonia?

Silver chloride (AgCl) dissolves in dilute ammonia. Silver bromide (AgBr) dissolves only in concentrated ammonia, while silver iodide (AgI) is insoluble in concentrated ammonia.

Test for ammonium ions, NH₄⁺.

Add sodium hydroxide solution and warm.

Ammonia gas is produced.

Damp red litmus paper turns blue.

Ionic equation: NH₄⁺ + OH⁻ → NH₃ + H₂O

Test for magnesium ions, Mg²⁺.

Add sodium hydroxide solution.

A white precipitate forms.

Ionic equation: Mg²⁺ + 2OH⁻ → Mg(OH)₂

Test for sulfate ions, SO₄²⁻.

Add barium chloride solution.

A white precipitate forms.

Ionic equation: Ba²⁺ + SO₄²⁻ → BaSO₄

Test for carbonate ions, CO₃²⁻.

Add dilute acid.

Effervescence/fizzing occurs as CO₂ is produced.

CO₂ turns limewater cloudy.

Ionic equation: CO₃²⁻ + 2H⁺ → CO₂ + H₂O

Test for chloride ions, Cl⁻.

Add silver nitrate solution.

A white precipitate forms.

Ionic equation: Ag⁺ + Cl⁻ → AgCl

Test for bromide ions, Br⁻.

Add silver nitrate solution.

A cream precipitate forms.

Ionic equation: Ag⁺ + Br⁻ → AgBrAdd silver nitrate solution.

A cream precipitate forms.

Ionic equation: Ag⁺ + Br⁻ → AgBr

Test for iodide ions, I⁻.

Test for copper(II) ions, Cu²⁺.

Add sodium hydroxide solution.

A blue precipitate forms.

Test for iron(II) ions, Fe²⁺.

Add sodium hydroxide solution.

A green precipitate forms.

Test for iron(III) ions, Fe³⁺.

Add sodium hydroxide solution.

A brown precipitate forms.

Test for aluminium ions, Al³⁺.

Add sodium hydroxide solution.

A white precipitate forms.

Test for calcium ions, Ca²⁺.

Add sodium hydroxide solution.

A white precipitate forms.

Physical properties of Group 7 at room temperature

Fluorine: pale yellow gas.

Chlorine: greenish-yellow gas.

Bromine: orange-brown liquid which vaporises easily into orange gas.

Iodine: black solid which vaporises on heating to purple gas.

Appearance and solubility of halogens

Halogens are sparingly soluble in water.

As you go down the group, they become less soluble.

Appearance of Cl2, Br2 and I2 in water and cyclohexane

Cl2: pale green in water and pale green in cyclohexane.

Br2: orange in water and orange in cyclohexane.

I2: brown in water and violet in cyclohexane.

Explain why atomic radius increases down Group 7.

The Group 7 elements increase in size going down the group because their number of electron energy levels increases.

Explain why melting point increases down Group 7.

Halogens are non-polar diatomic molecules.

They only have van der Waals forces between the molecules.

The strength of these depends on the size of the molecule and number of electrons.

Explain why melting point increases down Group 7.

Halogens are non-polar diatomic molecules.

They only have van der Waals forces between the molecules.

The strength of these depends on the size of the molecule and number of electrons.

What three factors affect electronegativity?

Greater nuclear charge will withdraw electrons more strongly.

Small atomic radius will withdraw electrons more strongly.

More shielding will reduce the withdrawal of electrons.

Describe the trend in electronegativity down Group 7.

Fluorine is the most electronegative.

Iodine towards the bottom of Group 7 is the least electronegative.

Define electronegativity.

The ability to withdraw an electron pair from a covalent bond.

Why are halogens oxidising agents? Give the equation for chlorine.

Halogens are oxidising agents because they gain electrons.

Cl2 + 2e- -> 2Cl-

Reaction between chlorine and sodium bromide: equation and explanation.

Cl2 + 2NaBr -> Br2 + 2NaCl

Chlorine is a more powerful oxidising agent.

Chlorine displaces bromide to form sodium chloride, and bromide is converted to bromine.

Reaction between chlorine and potassium fluoride: equation and explanation.

Cl2 + 2KF -> no reaction.

Fluorine is higher in Group 7 than chlorine.

Fluorine exists as fluoride ions and chlorine as chlorine molecules in the reactants.

Therefore, no reaction occurs.

What are the observations in halogen displacement reactions?

If bromine is produced, the mixture turns orange-brown.

If iodine is produced, a black solid forms.

Why are halide ions good reducing agents?

Halide ions are good reducing agents.

They are good at releasing their additional electron.

Reducing power increases down the group as electrons are easier to lose.

They form larger ions due to shielding and larger atomic radius.

Write the half-equations and overall ionic equations for bromide and iodide ions reacting with concentrated sulfuric acid, reducing sulfur from +6 to +4.

Bromide:

Oxidation half-equation:

2Br⁻ → Br₂ + 2e⁻

Reduction half-equation:

SO₄²⁻ + 4H⁺ + 2e⁻ → SO₂ + 2H₂O

Overall ionic equation:

SO₄²⁻ + 4H⁺ + 2Br⁻ → SO₂ + 2H₂O + Br₂

Iodide:

Oxidation half-equation:

2I⁻ → I₂ + 2e⁻

Reduction half-equation:

SO₄²⁻ + 4H⁺ + 2e⁻ → SO₂ + 2H₂O

Overall ionic equation:

SO₄²⁻ + 4H⁺ + 2I⁻ → SO₂ + 2H₂O + I₂

Write the half-equations and overall ionic equation for iodide ions reacting with concentrated sulfuric acid, reducing sulfur from +6 to 0.

Oxidation half-equation:

6I⁻ → 3I₂ + 6e⁻

Reduction half-equation:

SO₄²⁻ + 8H⁺ + 6e⁻ → S + 4H₂O

Overall ionic equation:

SO₄²⁻ + 8H⁺ + 6I⁻ → S + 4H₂O + 3I₂

Observation:

Yellow solid sulfur forms.

Write the half-equations and overall ionic equation for iodide ions reacting with concentrated sulfuric acid, reducing sulfur from +6 to −2 in H₂S.

Oxidation half-equation:

8I⁻ → 4I₂ + 8e⁻

Reduction half-equation:

SO₄²⁻ + 10H⁺ + 8e⁻ → H₂S + 4H₂O

Overall ionic equation:

SO₄²⁻ + 10H⁺ + 8I⁻ → H₂S + 4H₂O + 4I₂

Observation:

Hydrogen sulfide gas has a strong, unpleasant rotten-egg smell.

Acid-base reaction of solid sodium halides with concentrated sulfuric acid

NaX(s) + H₂SO₄(l) → NaHSO₄(s) + HX(g)

Ionic equation:

H⁺ + X⁻ → HX

Observation: White fumes of HX gas form.

This is an acid-base reaction.

Redox reaction of bromide and iodide ions with concentrated sulfuric acid

H₂SO₄ + 2HBr → Br₂ + SO₂ + 2H₂O

H₂SO₄ + 2HI → I₂ + SO₂ + 2H₂O

This is a redox reaction.

Br₂: orange-brown fumes.

I₂: purple vapour.

Why is chlorine used in drinking water and swimming pools?

Chlorine kills bacteria in small enough concentrations and is used in the treatment of drinking water and swimming pools. At these concentrations, it is not harmful to humans.

Write the equation and ionic equation for chlorine reacting with water.

Equation:

Cl₂ + H₂O ⇌ HClO + HCl

Ionic equation:

Cl₂ + H₂O ⇌ HClO + H⁺ + Cl⁻

Why is chlorine reacting with water a disproportionation reaction?

Chlorine starts at oxidation state 0.

It is reduced to −1 in HCl/Cl⁻ and oxidised to +1 in HClO at the same time.

Chlorine both gains and loses electrons.

What is HClO used for?

HClO kills bacteria in swimming pools by oxidising them.

Write the equation for chlorine reacting with water in bright sunlight.

2Cl₂(g) + 2H₂O(l) → 4HCl(aq) + O₂(g)

Explain the role of sodium hypochlorite in swimming pool water.

NaClO(s) + H₂O(l) ⇌ Na⁺(aq) + OH⁻(aq) + HClO(aq)

In alkaline solution, HClO is converted to ClO⁻ ions.

Swimming pool water is kept slightly acidic.

Write the equation for chlorine reacting with aqueous sodium hydroxide and state the use of the product.

Cl₂ + 2NaOH → NaClO + NaCl + H₂O

This is a disproportionation reaction.

Sodium hypochlorite, NaClO, is a key ingredient in bleach and is an oxidising agent.

What is the role of a halide ion in an acid-base reaction?

Proton acceptor

How can hydroxide ions be tested for?

Add red litmus paper.

It turns blue.

Why should too much chlorine not be added to water?

Chlorine is toxic and can cause death in humans.

Write the equation for chlorine reacting with sodium iodide and state the observation.

Cl₂ + 2I⁻ → 2Cl⁻ + I₂

Observation: Iodine is produced as a black solid.

Sulfuric acid + solid sodium iodide. State the role of sulfuric acid.

Oxidising agent