Question

\(\mathrm{MgCl}_{2} .6 \mathrm{H}_{2} \mathrm{O}\), when heated gives (a) magnesium hydride (b) magnesium chloride (c) magnesium oxide (d) magnesium axychloride

Short answer

(b) Heat \\( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \\) to get anhydrous magnesium chloride, \\( \text{MgCl}_2 \\). Answer: (b) magnesium chloride.

Step-by-step solution

Identify the given compound

The compound given is magnesium chloride hexahydrate, \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \). This means that magnesium chloride is associated with six molecules of water of crystallization.

Understand the reaction upon heating

Upon heating, the water molecules associated with \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \) are removed. This process is called dehydration dissociation where the compound loses water to yield anhydrous magnesium chloride.

Predict the product

When \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \) is heated and water is removed, the remaining product is anhydrous magnesium chloride, \( \text{MgCl}_2 \). Magnesium hydride, magnesium oxide, and magnesium axychloride are not typically formed from this compound upon heating.

Key concepts

Anhydrous Magnesium Chloride

Anhydrous magnesium chloride, often represented as \( \text{MgCl}_2 \), is the form of magnesium chloride that is free from water. It is obtained from magnesium chloride hexahydrate \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \) by removing the water through a process called dehydration. This process involves heating the hydrate, which results in the release of the six water molecules. The end result is a compound devoid of water, hence the term "anhydrous."

Anhydrous magnesium chloride plays a key role in several industrial applications. It is used in the production of pure magnesium metal. Additionally, it serves as a catalyst in various chemical reactions. Understanding what "anhydrous" means is important because it indicates that a compound is free of water, which could otherwise affect its chemical and physical properties.

Importance of Anhydrous Compounds

Anhydrous forms of compounds have significant implications in industrial and chemical processes:

• They are stable and predictable because they lack the variable of water content.
• Water-free compounds generally have higher solubility in non-polar solvents compared to their hydrated counterparts.

Water of Crystallization

Water of crystallization is a key concept in understanding certain hydrated salts, such as magnesium chloride hexahydrate \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \). It refers to water molecules that are chemically bonded within a crystalline structure of a compound. These water molecules are not merely trapped in the crystal; they are integral to the stability and shape of the crystal.

When a compound like \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \) is heated and loses these waters of crystallization, it undergoes a transformation, usually becoming an anhydrous form as seen with magnesium chloride. This loss of water is a reversible process if the compound is exposed to moisture again, potentially reverting back to its hydrated form.

Role in Chemistry

Water of crystallization influences many properties of the compound, such as:

• Thermal stability: Hydrated forms often have different stability compared to anhydrous forms.
• Physical properties: Crystals with water of crystallization have different textures and appearances.
• Chemical reactivity: The presence of water can facilitate or inhibit certain reactions.

Chemical Reaction Predictions

Chemical reaction predictions are a fundamental aspect of understanding how substances interact. In the case of heating magnesium chloride hexahydrate, certain predictions can be made based on the composition and nature of the substances involved. Given that \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \) is a hydrated compound, the most probable reaction upon heating is the loss of water to produce an anhydrous product.

In this scenario, predicting that the products of heating \( \text{MgCl}_2 \cdot 6 \text{H}_2\text{O} \) are other than anhydrous magnesium chloride would be incorrect based on the chemistry of the compound. The predictions are grounded in the chemical principles of dehydration. Understanding this allows chemists and students alike to foresee the results of heating and comprehend potential industrial applications.

Making Accurate Predictions

Accurate predictions require understanding the compound's properties and behaviors:

• Analyze the chemical nature of the compound: Knowing whether it is prone to losing elements like water is crucial.
• Study similar reactions: Previous observations help inform what might occur under similar circumstances.
• Consider energy changes: Heat often provides the essential energy to drive processes like dehydration.