Question

Milk of magnesia, a widely used antacid, is an aqueous suspension of \(\mathrm{Mg}(\mathrm{OH})_{2}\). How would you prepare \(\mathrm{Mg}(\mathrm{OH})_{2}\) from magnesium metal?

Short answer

React magnesium with water to form \( \mathrm{Mg(OH)}_2 \) solid.

Step-by-step solution

Identifying the Reaction

To prepare \( \mathrm{Mg(OH)}_2 \), magnesium metal needs to react with water. The general reaction for this is \( \mathrm{Mg} + 2\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Mg(OH)}_2 + \mathrm{H}_2 \). This reaction involves magnesium metal reacting with water to form magnesium hydroxide and hydrogen gas.

Setting Up the Experiment

You would need a piece of magnesium metal and enough distilled water to submerge it. Using a beaker or a similar container, place the magnesium metal in the water. Ensure safety precautions like wearing goggles and gloves to handle the gases produced.

Conducting the Reaction

Allow the magnesium to sit in the water. Magnesium will react slowly with water, possibly requiring gentle heating to increase the rate of reaction. As the reaction proceeds, bubbles of hydrogen gas \( \mathrm{H}_2 \) will form, and \( \mathrm{Mg(OH)}_2 \) will precipitate.

Collection and Filtration

Once the reaction is complete, let the \( \mathrm{Mg(OH)}_2 \) settle if it hasn't already precipitated. The \( \mathrm{Mg(OH)}_2 \) can then be collected by filtration. This ensures that you separate the solid magnesium hydroxide from the liquid.

Washing and Drying

Wash the \( \mathrm{Mg(OH)}_2 \) solid with distilled water to remove any impurities or unreacted substances. After washing, let the \( \mathrm{Mg(OH)}_2 \) dry in a suitable environment, such as in an oven at low temperature or left at room temperature.

Key concepts

Magnesium Hydroxide

Magnesium hydroxide, represented by the chemical formula \( \mathrm{Mg(OH)}_2 \), is a white solid that is sparingly soluble in water. It is widely known for its use as an active ingredient in antacids and laxatives, commonly referred to as "milk of magnesia." As an alkaline substance, magnesium hydroxide works by neutralizing stomach acid, hence its antacid properties. It is naturally occurring in the mineral brucite. Though in industrial settings, the compound can be synthesized through the reaction of magnesium compounds with water or diluted acids. Understanding its properties is crucial in comprehending how this compound interacts in various chemical processes, especially those involving its medicinal uses.

Antacid Preparation

The preparation of antacids like milk of magnesia involves transforming raw magnesium into magnesium hydroxide. This is achieved through a chemical reaction where magnesium metal is allowed to react with water. The overall chemical reaction is:

• \( \mathrm{Mg} + 2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Mg(OH)}_2 + \mathrm{H}_2 \)

In this reaction, magnesium reacts with water molecules to yield magnesium hydroxide and hydrogen gas. The freshly prepared compound can then be further processed into a suspension suitable for medical use. Antacid preparations are crucial in managing and relieving symptoms of acidity and indigestion. Manufacturing these products requires precision to ensure that the magnesium hydroxide is pure and effective while maintaining safety standards.

Aqueous Suspension

An aqueous suspension is when solid particles are dispersed throughout a liquid, but not dissolved in it. For magnesium hydroxide, the suspension is the form in which it is typically consumed as an antacid. The particles of \( \mathrm{Mg(OH)}_2 \) remain suspended in water, creating a milky appearance known as milk of magnesia.This form is useful because the fine particles increase the surface area available for reaction with stomach acid, making it more effective in neutralization. Maintaining a uniform suspension where particles do not settle quickly requires proper preparation techniques, including thorough mixing and the use of additives that help keep particles evenly distributed.

Chemical Filtration

Chemical filtration is an essential step in the preparation of magnesium hydroxide from magnesium metal. After allowing the magnesium to react with water and precipitate out as magnesium hydroxide, separating the solid from the liquid is crucial. Filtration involves passing the mixture through a medium—typically a filter paper—where the solid \( \mathrm{Mg(OH)}_2 \) is trapped and the liquid is allowed to pass through.

• This process ensures a pure product, free from impurities and unreacted magnesium.
• It also prevents the contamination of the \( \mathrm{Mg(OH)}_2 \) with any gases such as hydrogen that may be produced during the reaction.

Once collected, the \( \mathrm{Mg(OH)}_2 \) is washed with distilled water to remove any remaining impurities. Proper drying is necessary to maintain the integrity and efficacy of magnesium hydroxide, especially when used in pharmaceutical applications like antacids.