Catalysis and precipitation 206-207

Question 1

Explain the two ways in which transition metal catalysis takes place.

Answer 1

• Transition metals provide a surface on which a reaction can take place. Reactants are adorbed into the surface of the metal and held in place while a reaction occurs. After the reaction, the products are desorbed and the metal remains unchanged.
• Transition metal ions have the ability to change oxidation states by gaining or losing electrons. They then bind to reactants forming intermediates as part of a chemical pathway with a lower activation energy.

Question 2

• Write out the reaction for the Haber process
• What catalyst is used
• What is the product formed from the Haber process used for?

Answer 2

N₂(g) + 3H₂(g) ⇔ 2NH₃(g)

• The catalyst is iron metal - it is used to increase the rate of reaction and to lower the temperature at which the reaction takes place.

Much of the ammonia produced in the Haber process is used in manufacturing fertilisers.

Question 3

Write out the reaction for the contact process.

• Explain the catalyst used.
• Explain what the product of the reaction is used for.

Answer 3

2SO₂(g) + O₂(g) ⇔ 2SO₃(g)

• The catalyst used in vanadium(V) oxide, V₂O_5,in which vanadium has the +5 oxidation state.
• Sulfuric acid is an important inorganic chemical with many uses, including the production of fertilisers, detergents, adhesives and explosives, and as the electrolyte in car batteries.

Question 4

Write out the reaction for the hydrogenation of alkenes.

• Explain the catalyst used.
• Describe what the products are used for.

Answer 4

CH₂CH₂+ H₂ ⇒ CH₃CH₃

• The catalyst is nickel metal - it is used to lower the temperature and pressure needed to carry out the reaction.
• This process is used in the hydrogenation of unsaturated vegetable oils to make spreadable margarines.

Question 5

Write out the reaction for the decomposition of hydrogen peroxide.

• Explain the catalyst used.
• What is the product used for?

Answer 5

2H₂O₂(aq) → 2H₂O(l) + O₂(g)

• A suitable catalyst is manganese(IV) oxide, MnO₂m in which manganese has the +4 oxidation state. Manganese (IV) oxide is commonly called manganese dioxide.

The catalytic decomposition of hydrogen peroxide is often used in the laboratory as a simple and convenient preparation of oxygen gas.

Question 6

What is the colour change and reaction when a solution of copper(II) ions reacts with aqueous sodium hydroxide to form a coloured precipitate of copper(II) hydroxide.

Answer 6

Cu²⁺(aq) + 2OH^-(aq) → Cu(OH)₂ (s)

• Cu²⁺ is a pale blue solution
• Cu(OH)₂ is a pale blue precipitate.

Question 7

Write the equation and observation when a solution of Co²⁺(aq) reacts with NaOH.

Answer 7

• A pink solution containing Co²⁺(aq) reacts to form a blue precipitate- turning beige in the presence of air.

Co²⁺(aq) + 2OH^-(aq) → Co(OH)₂(s)

• Precipitate is colbat(II) hydroxide.

Question 8

Write the equation and observation when a solution of Fe²⁺(aq) reacts with NaOH.

Answer 8

• Pale green solution containing Fe²⁺(aq) forms a green precipitate - turning a rusty brown at its surface on standing air.( the precipitate changes colour because green Fe²⁺ ions are readily oxidised to rusty-brown Fe³⁺ ions.

Fe²⁺(aq) + 2OH^-(aq) → Fe(OH)₂(s)

Precipitate is iron(II) hydroxide.

Question 9

Write the equation and observation when a solution of Fe³⁺(aq) reacts with NaOH.

Answer 9

Pale yellow solution containing Fe³⁺(aq) forms a rusty-brown precipitate.