Titanium is extracted from an ore called rutile. Rutile is an impure form of titanium(IV) oxide, TiO2.
(a) Rutile is mixed with coke and heated in a furnace through which chlorine gas is passed. The product is gaseous titanium(IV) chloride, TiCl4.
TiO2(s) + 2C(s) + 2Cl2(g) → TiCl4(g) + 2CO(g)
The gaseous titanium(IV) chloride produced is condensed into the liquid state. The titanium(IV) chloride is then separated from liquid impurities.
(i) Suggest the name of the process by which liquid titanium(IV) chloride could be separated from the liquid impurities.
(ii) Carbon monoxide, CO(g), is also produced in the reaction.
Why should carbon monoxide not be released into the atmosphere?
(b) Calculate the volume of chlorine gas, Cl2(g), at room temperature and pressure, that reacts completely with 400g of TiO2(s) using the following steps.
TiO2(s) + 2Cl2(g) + 2C(s) → TiCl4(g) + 2CO(g)
- Calculate the relative formula mass, Mr, of TiO2.
- Calculate the number of moles in 400g of TiO2.
- Determine the number of moles of Cl2 that react with 400g of TiO2.
- Calculate the volume of Cl2 that reacts with 400g of TiO2.
(c) Titanium(IV) chloride, TiCl4, is heated with an excess of magnesium, in an atmosphere of argon.
(i) Balance the chemical equation for the reaction.
TiCl4 + ….. Mg → Ti + ….. MgCl2
(ii) Titanium(IV) chloride can be reacted with sodium instead of magnesium.
The reaction between titanium(IV) chloride and sodium is similar to the reaction between titanium(IV) chloride and magnesium.
Write a chemical equation for the reaction between titanium(IV) chloride and sodium.
(iii) Suggest why the reaction between titanium(IV) chloride and magnesium is done in an atmosphere of argon and not in air.
(d) After titanium(IV) chloride is heated with magnesium, the unreacted magnesium is removed by adding an excess of dilute hydrochloric acid to the mixture.
The dilute hydrochloric acid also dissolves the magnesium chloride.
The dilute hydrochloric acid does not react with the titanium or dissolve it.
(i) Give two observations and write a chemical equation for the reaction that occurs when dilute hydrochloric acid reacts with magnesium.
(ii) Name the process that is used to separate the titanium from the mixture after all the magnesium has been removed.
(iii) Titanium does not react with the dilute hydrochloric acid or dissolve in it.
Suggest why titanium does not react with dilute hydrochloric acid.
(e) Magnesium cannot be produced by electrolysis of aqueous magnesium chloride using inert electrodes.
(i) Name the product formed at the negative electrode (cathode) during the electrolysis of aqueous magnesium chloride.
(ii) Suggest how magnesium can be produced from magnesium chloride by electrolysis.
▶️ Answer/Explanation
(a)(i) The process is fractional distillation, as TiCl4 and impurities have different boiling points.
(ii) Carbon monoxide is toxic—it binds irreversibly to hemoglobin, preventing oxygen transport.
(b) Step-by-step calculation:
– Mr(TiO2) = 48 (Ti) + 2×16 (O) = 80.
– Moles of TiO2 = 400g ÷ 80g/mol = 5 mol.
– Moles of Cl2 = 5 × 2 = 10 mol (from stoichiometry).
– Volume of Cl2 = 10 mol × 24 dm3/mol = 240 dm3.
(c)(i) Balanced equation: TiCl4 + 2Mg → Ti + 2MgCl2.
(ii) With sodium: TiCl4 + 4Na → Ti + 4NaCl.
(iii) Argon is used because magnesium reacts violently with oxygen/nitrogen in air.
(d)(i) Observations: Effervescence (H2 gas) and magnesium dissolves.
Equation: Mg + 2HCl → MgCl2 + H2.
(ii) Separation method: Filtration (titanium is insoluble).
(iii) Titanium is below hydrogen in the reactivity series (less reactive).
(e)(i) Cathode product: Hydrogen (H2) (water is reduced instead of Mg2+).
(ii) Magnesium is produced by electrolyzing molten MgCl2, not aqueous.
Period 3 contains the elements sodium to argon. This question asks about the chemistry of each of the Period 3 elements or their compounds.
(a) Sodium nitrate is a white crystalline solid. When heated it melts and the following reaction occurs.
\(2NaNO_3(l) \rightarrow 2NaNO_2(l) + O_2(g)\)
A 3.40g sample of sodium nitrate is heated. Calculate the
- number of moles of \(NaNO_3\) used,
- number of moles of \(O_2\) formed,
- volume of \(O_2\) formed, in \(dm^{3}\) (measured at r.t.p.).
(b) Magnesium reacts slowly with warm water to form a base, magnesium hydroxide.
(i) Explain what is meant by the term base.
(ii) Write a chemical equation for the reaction between magnesium and warm water.
(c) Aluminium oxide is amphoteric. It is insoluble in water. Describe experiments to show that aluminium oxide is amphoteric.
(d) Silicon(IV) oxide has a giant structure.
(i) Name the type of bonding in silicon(IV) oxide.
(ii) Give two physical properties of silicon(IV) oxide.
(e) Calcium phosphate is used in fertilisers. The bonding in calcium phosphate is ionic. Calcium phosphate contains the phosphate ion, \(PO_4^{3-}\).
(i) What is ionic bonding?
(ii) Deduce the formula of calcium phosphate.
(f) Sulfur tetrafluoride, \(SF_4\), can be made by combining gaseous sulfur with fluorine.
\(S(g) + 2F_2(g) \rightarrow SF_4(g)\)
The reaction is exothermic.
(i) Complete the energy level diagram for this reaction. Include an arrow which clearly shows the energy change during the reaction.
(ii) During the reaction the amount of energy given out is 780kJ/mol.
The F–F bond energy is 160kJ/mol.
Use this information to determine the bond energy, in kJ /mol, of one S–F bond in \(SF_4\).
(g) Chlorine and compounds of chlorine are important in water treatment and in laboratory testing for water.
(i) Chlorine is added to water to make the water safe to drink.
Explain why adding chlorine makes water safe to drink.
(ii) A compound of chlorine is used in the laboratory to test for the presence of water.
Name the compound of chlorine used in this test and describe the colour change seen in a positive result of this test.
(h) Argon is an unreactive noble gas.
(i) Explain why argon is unreactive.
(ii) Give one use of argon.
▶️ Answer/Explanation
(a)
• Moles of \(NaNO_3\): \(\frac{3.40}{85} = 0.04\) mol.
• Moles of \(O_2\): \(\frac{0.04}{2} = 0.02\) mol (from stoichiometry).
• Volume of \(O_2\) at r.t.p.: \(0.02 \times 24 = 0.48 dm^3\).
(b)
(i) A base is a proton (\(H^+\)) acceptor.
(ii) \(Mg(s) + 2H_2O(l) \rightarrow Mg(OH)_2(aq) + H_2(g)\).
(c) To show amphoteric nature:
1. React \(Al_2O_3\) with HCl (dissolves in acid).
2. React \(Al_2O_3\) with NaOH (dissolves in alkali).
Forms salts in both cases.
(d)
(i) Covalent bonding.
(ii) High melting point and hardness.
(e)
(i) Ionic bonding is the electrostatic attraction between oppositely charged ions.
(ii) Formula: \(Ca_3(PO_4)_2\).
(f)
(i) Exothermic diagram: Products lower than reactants, labeled \(SF_4\), arrow downward.
(ii) S–F bond energy:
1. Energy to break \(2F_2\): \(2 \times 160 = 320\) kJ/mol.
2. Total energy for \(SF_4\): \(780 + 320 = 1100\) kJ/mol.
3. Per S–F bond: \(\frac{1100}{4} = 275\) kJ/mol.
(g)
(i) Chlorine kills bacteria/pathogens.
(ii) Cobalt(II) chloride; color change from blue to pink.
(h)
(i) Argon has a full outer electron shell (stable octet).
(ii) Used in lamps (inert atmosphere).