Uses of Group 2 Elements (AQA A-Level Chemistry): Revision Notes

2.2.4 Uses of Group 2 Elements

Group 2 elements such as magnesium, calcium, and barium have a wide range of important industrial and medical applications. These uses are based on the properties of their compounds, particularly their solubility and reactivity.

Magnesium in Titanium Extraction

Magnesium is crucial in the extraction of titanium from its ore. Titanium is commonly found in nature as titanium(IV) oxide ($TiO₂$).

The extraction process involves:

• Step 1: Titanium(IV) oxide is first converted to titanium(IV) chloride ($TiCl₄$) by heating it with carbon in a stream of chlorine gas.
• Step 2: The titanium chloride is purified by fractional distillation and then reduced by magnesium in a furnace at nearly 1000°C. The reaction is as follows:

$$\text{TiCl}_4(g) + 2\text{Mg(l)} \rightarrow \text{Ti(s)} + 2\text{MgCl}_2(l)$$

This method produces pure titanium, which is used in various industries, including aerospace and medical implants.

Magnesium Hydroxide in Medicine

Magnesium hydroxide, $Mg(OH)₂$, is commonly known as "milk of magnesia". It is used in medicine for:

• Neutralising stomach acid: It acts as an antacid, relieving indigestion and heartburn by neutralising excess stomach acid.
• Laxative: Its low solubility ensures a gentle laxative effect without being absorbed into the bloodstream.

Calcium Hydroxide in Agriculture

Calcium hydroxide, $Ca(OH)₂$, also known as "slaked lime", is widely used in agriculture:

• It neutralises acidic soil, making the soil more suitable for plant growth.
• Calcium hydroxide is applied to improve soil pH for optimal crop production, which is essential for food supply.

Removal of $SO₂$ from Flue Gases

Both calcium oxide ($CaO$) and calcium carbonate ($CaCO₃$) are used in industry to remove sulphur dioxide ($SO₂$) from flue gases, a byproduct of fossil fuel combustion. This process helps to prevent the formation of acid rain:

$$\text{CaO/CaCO}_3 + \text{SO}_2 \rightarrow \text{CaSO}_3$$

This is an important application in reducing environmental pollution from industrial emissions.

Barium Sulphate in Medicine

Barium sulphate, $BaSO₄$, is used in medical imaging:

• Barium meals: Patients consume a suspension of $BaSO₄$, which absorbs X-rays. Since barium sulphate is insoluble, it outlines the digestive tract without being absorbed by the body. This allows doctors to obtain clear X-ray images of the intestines. While barium ions are toxic, $BaSO₄$ is safe because it is highly insoluble, meaning it passes through the digestive system without being absorbed into the bloodstream.

Testing for Sulphate Ions with Barium Chloride

A solution of acidified barium chloride ($BaCl₂$) is used to test for sulphate ions in a solution. The acidification ensures no other ions, like carbonate ions, interfere with the test:

$$\text{Ba}^{2+} + \text{SO}_4^{2-} \rightarrow \text{BaSO}_4(s)$$

This forms a white precipitate of barium sulphate, confirming the presence of sulphate ions. The solution is acidified with hydrochloric acid to prevent false positive results from carbonate ions, which could also form a white precipitate.