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Question 1

Method used to reduce Al₂O₃ on an industrial scale and conditions

Answer 1

• Electrolysis
• High Temp (500-1500 C)
• Dissolved in molten Cryolite

Question 2

Why is more energy needed to boil HF greater than that of NH₃

Answer 2

• H bonding in both
• But it’s stronger in HFas H—F is more polar than H—N
• As electronegativity of F > N
• More energy needed to overcome forces

Question 3

How do we convert [Cr(H₂O)₆]³⁺ to CrO₄^2-

Answer 3

• Add H₂O₂ and NaOH

Question 4

How do we converted VO₂⁺ to [V(H₂O)₆]²⁺

Answer 4

• Add Zn and HCl

Question 5

Convert [Ag(NH₃)₂]⁺ to Ag

Answer 5

• Add SPECIFIC aldehyde, so Ethanal

Question 6

Write an equation for the reduction of Ti under an intert atmosphere and explain why air is excluded?

Answer 6

• TiCl₄ + 4Na⇒ 4NaCl + Ti
• O₂ in air would oxidise Ti

Question 7

How would you work out the % of Fe³⁺ in a solution with only Fe²⁺ and Fe³⁺

You have: Zn,K₂Cr₂O₇, H₂SO₄

Answer 7

1. Cr₂O₇^2- + 14H⁺ + 6Fe²⁺ → 6Fe^{<span>3+ </span>}+ 2Cr³⁺ + 7H2O
2. Zn + 2Fe³⁺ → Zn²⁺ +2Fe²⁺
3. Titrate known voume of mixture against K₂Cr₂O₇
4. Reduce the same volume with Zn
5. Filter off excess Zn
6. Titrate total volume of mixture using K₂Cr₂O₇
7. % = 100x(T₂-T₁)/T₂

Question 8

Factors that affect the efficiency of this reaction

0.5N₂ + 1.5H₂ → NH₃ ΔH= -ve

Answer 8

• The higher the temperature the faster the reaction
• This is due to the increased kinetic energy
• But, since the reaction is exothermic the equilibrium yield is lower at a higher temp
• The higher the pressure the greater the equilibrium yield
• Because there is a reduction in the number of moles of gas in the reaction
• But higher pressure is expensive to produce and vessels to withstand pressure is more expensive to build
• A Fe catalyst would lessen the time to reach equilibrium and allow more ammonia to be produced in a given time
• Would reduce the Ea

Question 9

How would you explain how a Na atom is larger than a Cl atom but a Na+ ion is smaller than Cl-

Answer 9

1. A chlorine atom has more protons in its nucleus than has a sodium atom
2. Both have 3 shells of electrons, so constant shielding
3. Electrons more strongly attracted by chlorine nucleus so smaller atomic radius than Na
4. An electron shell is lost when a sodium ion is formed from a sodium atom
5. Inner electrons more strongly attracted so ion smaller than atom
6. An electron is added to the outer shell when a chloride ion is formed
7. Greater repulsion between shells so size of chloride ion greater than Cl atom

Question 10

Why may the ΔH_f may be similar/ dissimilar to ΔHc of water that of H₂

Answer 10

• same number and type reactants and same products
• There must be a slight difference between the actual bond enthalpy and mean bond enthalpies for the O–H bond in other molecules

Question 11

Suggest why aluminium is not extracted by electrolysis of AlCl₃ but it can for Al₂O₃

Answer 11

• aluminium chloride is covalent;
• aluminium chloride does not conduct electricity;
• aluminium chloride does not occur naturally;
• manufacture of AlCl₃ costly as chlorine is expensive;