Uses of Group 2 (Oxford AQA International A Level Chemistry)

Uses of Group 2

Uses of Magnesium

Medicine

• Magnesium hydroxide, Mg(OH)₂, is sparingly soluble in water and is used in suspension (known as 'milk of magnesia') to neutralise excess acid in the stomach and treat constipation

Mg(OH)₂ (s) + 2HCl (aq) → MgCl₂ (aq) + 2H₂O (l)

• It is safe to use as the magnesium hydroxide is only partially soluble making the solution only slightly alkaline (pH ≅ 10) due to the low OH^- concentration

Extraction of titanium

• Magnesium is also used in the extraction of titanium from its ore, TiO₂

• TiO₂ is heated in a stream of chlorine, in the presence of coke, to produce TiCl₄

TiO₂ (s) + 2C (s) + 2Cl₂ (g) → TiCl₄ (g) + 2CO (g)

• The titanium is extracted from its chloride by reduction with magnesium (sodium can also be used)

TiCl₄ (g) + 2Mg (l) → Ti (s) + 2MgCl₂ (l)

Uses of Calcium

Agriculture

• Three different calcium compounds are used commonly in agriculture, construction and iron extraction:

  • Limestone - this is impure calcium carbonate

  • Quicklime - this is calcium oxide, formed by the thermal decomposition of calcium carbonate

  • Slaked lime - this is calcium hydroxide formed when water is added to quicklime

• All three materials are used in agriculture to raise the pH of the soil

  Ca(OH)₂ (s) + 2H⁺ (aq) → Ca²⁺ (aq) + 2H₂O (l)

• The optimum pH for many crops to grow is at around 6-6.5

• The compounds are all bases and react with the acids in the soil to raise its pH

• Calcium carbonate (limestone) is more commonly used in agricultural lime as it is cheaper and safer to handle

  • However, due to it being sparingly soluble, it acts more slowly than calcium hydroxide

Reducing sulfur dioxide emissions

• Calcium compounds are also used to remove sulfur dioxide from flue gases in a process known as sulfur scrubbing

• The main way to reduce sulfur dioxide emissions is to treat the waste gases from coal fired power stations 

• The waste gases are passed into a scrubbing chamber which sprays a wet slurry of calcium oxide and calcium carbonate into the gases

  • This process is also known as sulfur scrubbing or flue gas desulfurisation

• Calcium oxide or calcium carbonate can be used to form calcium sulfite

CaO (s) + SO₂ (g) → CaSO₃ (s)

CaCO₃ + SO₂ (g) → CaSO₃ (s) + CO₂ (g)

• This is then oxidised to calcium sulfate (gypsum)

CaSO₃ (s) + ½O₂ (g) → CaSO₄ (s)

Sulfur dioxide scrubber

Uses of Barium

• Barium is used in medicine in the form of barium sulfate, BaSO₄

• A barium meal or barium swallow containing BaSO₄ is given to a patient who needs an X-ray on their intestines

• Barium absorbs X-rays which means the gut shows up white on the image

• Barium is toxic though can be used in this form because:

  • Barium sulfate is insoluble so is not absorbed into the blood

  • The barium meal or swallow is only a small amount for the patient to ingest

• Barium chloride or barium nitrate solution can also be used to test for the presence of sulfate ions