Uses of Group 2 Elements (AQA AS Chemistry)

Uses of Calcium

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

• All three materials are used in agriculture to raise the pH of the soil
• Over time, the soil becomes more acidic while 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 and raise the pH of the soil
• Calcium carbonate is more commonly used in agricultural lime as it is cheaper and safer to handle
  • However, due to calcium carbonate being largely insoluble, it acts more slowly than calcium hydroxide

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

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 be used in the test for sulfate ions, SO₄^2-

Uses of Magnesium

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

• 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
• 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)