Understanding Milk of Magnesia: Chemical Name

The question asks for the chemical name commonly known as Milk of Magnesia. Milk of Magnesia is a well-known over-the-counter medication used primarily to relieve constipation and indigestion.

To identify the correct chemical name, let's look at the provided options and understand what Milk of Magnesia is composed of.

Identifying Milk of Magnesia

Milk of Magnesia is an aqueous suspension of magnesium hydroxide. It is called "milk" because of its milky, white appearance, which is due to the suspension of solid magnesium hydroxide particles in water.

Its primary active ingredient is magnesium hydroxide, which has the chemical formula $\text{Mg(OH)}_2$.

Analyzing the Options for Milk of Magnesia

Let's examine each option provided:

1. Magnesium bicarbonate: The chemical formula for magnesium bicarbonate is $\text{Mg(HCO}_3\text{)}_2$. This compound is typically found in hard water. It is not known as Milk of Magnesia.
2. Magnesium carbonate: The chemical formula for magnesium carbonate is $\text{MgCO}_3$. Magnesium carbonate is also used as an antacid and a laxative, but it is not the substance known as Milk of Magnesia. It is a white solid.
3. Magnesium sulphate: The chemical formula for magnesium sulphate is $\text{MgSO}_4$. This compound, particularly its hydrated form ($\text{MgSO}_4 \cdot 7\text{H}_2\text{O}$), is commonly known as Epsom salt. It is used as a laxative and for baths, but it is not Milk of Magnesia.
4. Magnesium hydroxide: The chemical formula for magnesium hydroxide is $\text{Mg(OH)}_2$. As discussed earlier, an aqueous suspension of magnesium hydroxide is precisely what is known as Milk of Magnesia. It acts as an antacid by neutralizing stomach acid ($\text{HCl}$) according to the reaction: $\text{Mg(OH)}_2\text{(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + 2\text{H}_2\text{O(l)}$. It also acts as a laxative by drawing water into the intestines.

Based on the analysis of the options, Magnesium hydroxide is the chemical compound that is known as Milk of Magnesia when suspended in water.

Conclusion

Milk of Magnesia is the common name for an aqueous suspension of magnesium hydroxide. Therefore, the correct option is Magnesium hydroxide.

Revision Table: Magnesium Compounds

Additional Information on Milk of Magnesia and Magnesium Hydroxide

Magnesium hydroxide ($\text{Mg(OH)}_2$) is an inorganic compound. It is a white solid that is practically insoluble in water. However, when mixed with water, it forms a suspension, which is the familiar "Milk of Magnesia".

• Antacid Action: Magnesium hydroxide neutralizes excess stomach acid, providing relief from heartburn and indigestion. Its relative insolubility means it reacts slowly and doesn't cause a significant rebound increase in stomach acid production.
• Laxative Action: When taken in larger doses, magnesium hydroxide acts as an osmotic laxative. Magnesium ions are poorly absorbed from the digestive tract. The presence of these ions draws water from the surrounding tissues into the intestines, which softens the stool and increases bowel activity.
• Safety and Side Effects: While generally safe for short-term use, excessive doses or prolonged use can lead to magnesium toxicity, especially in individuals with kidney problems. Common side effects include diarrhea.
• Suspension: Milk of Magnesia needs to be shaken well before use because it is a suspension, meaning the solid particles of magnesium hydroxide settle over time.

Understanding the chemical composition helps explain how Milk of Magnesia functions as both an antacid and a laxative, depending on the dosage.