An eight year old was asked, 'What do you think is a cation?'

Her quick reply was a positively charged kitten.


How does milk of magnesia work?

If you don't eat on time, you get a feeling of uneasiness and stomach pain, right? Adults call it acidity. Let's see what it means, and how milk of magnesia can cure it.

What is acidity?

Our stomach produces hydrochloric acid. This acid has many uses. It kills the germs in the food that might have survived even after cooking. It breaks down some of the carbohydrates and proteins, making them easier to digest.

When it is time for a meal, the stomach starts producing acid. Normally, since we eat something at mealtime, the acid gets to work. But if we don't eat anything, there is nothing for the acid to react with. So it starts attacking the lining of the stomach. That's what causes feelings of heartburn, pain and uneasiness.

Acid-base reaction

The acid-base reaction is one of chemistry's most important reactions. An acid is a substance that dissolves in water to release hydrogen ions. A base is any chemical that can accept these protons. This reaction is also called neutralisation.

Hence, when we get acidity, we need something that will neutralise the acid. One such chemical is sodium bicarbonate (baking soda). It's often made as a fizzy solution. But if fizzes out too fast, it is not very useful. Also some people don't like the burping sensation when carbon dioxide escapes.

NaHCO3 + HCL → NaCl + CO2 + H2O

You can take milk of magnesia instead. It is made of magnesium hydroxide (Mg(OH)2), which does not dissolve in water. When the powder is shaken with water, it forms a milk-like mixture. It's often sold as suspension or as chewable tablets. It reacts with the stomach acid to form water and magnesium chloride.

2HCl + Mg(OH)2 → MgCl2 + 2H2O

More on milk of magnesia

A side effect of taking milk of magnesia is that it causes diarrhea and water loss. Hence you should take no more than you need, and be sure to take lots of water.

For the same reason, milk of magnesia can also be used as a laxative when you have constipation. The magnesium ions in it cause water to accumulate in the intestine, and stimulate the release of enzymes. That makes the intestinal muscles to start contracting and releasing. That helps digestion and bowel movements.

Milk of magnesia was patented by Charles Henry Philips in 1873. It's a useful chemical to have in the house. But like all chemicals, it's always best when balanced!



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