Problem 71 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following compound is known as white vitriol? (a) \(\mathrm{ZnSO}_{4^{*}} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{CaCO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{MgSO}_{4^{*}} 7 \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

White vitriol is (a) \( \mathrm{ZnSO}_4 \cdot 7 \mathrm{H}_2 \mathrm{O} \).

Step 1: Identify the compounds' common names

Start by identifying the common names of the given compounds:- (a) \( \mathrm{ZnSO}_4 \cdot 7 \mathrm{H}_2\mathrm{O} \) is zinc sulfate heptahydrate.- (b) \( \mathrm{Na}_2\mathrm{SO}_4 \cdot 10 \mathrm{H}_2\mathrm{O} \) is sodium sulfate decahydrate, known as Glauber's salt if it were decahydrate.- (c) \( \mathrm{CaCO}_4 \cdot 2 \mathrm{H}_2\mathrm{O} \) seems to be a typo or a non-existent compound; it does not exist with such a formula.- (d) \( \mathrm{MgSO}_4 \cdot 7 \mathrm{H}_2\mathrm{O} \) is magnesium sulfate heptahydrate, known as Epsom salt.

Step 2: Recognize the White Vitriol

The compound known as "white vitriol" is zinc sulfate, specifically the heptahydrate form. Hence, option (a) \( \mathrm{ZnSO}_4 \cdot 7 \mathrm{H}_2 \mathrm{O} \) is known as white vitriol.

Step 3: Verify by eliminating other options

To further confirm, consider the other options: - Option (b), sodium sulfate, is known by different names but not white vitriol. - Option (c) is an incorrect formula. - Option (d), magnesium sulfate, has a different common name (Epsom salt). Thus, only (a) matches the name "white vitriol."

Key Concepts

Zinc Sulfate

Zinc sulfate is a well-known inorganic compound composed of zinc, sulfur, and oxygen. Its chemical formula is \(\mathrm{ZnSO}_4\). Zinc sulfate appears as a white crystalline solid and is soluble in water. It is often found in a hydrated form, where water molecules are incorporated into its structure.

Zinc sulfate has several applications both in industry and healthcare. It’s a critical ingredient in agriculture as a zinc supplement for crops. In medical fields, it is used to treat zinc deficiency and associated conditions.

The most common hydrated form of zinc sulfate is the heptahydrate \(\mathrm{ZnSO}_4 \cdot 7 \mathrm{H}_2\mathrm{O}\), also known as white vitriol. This nomenclature stems from historical names used by alchemists, where "vitriol" referred to sulfate compounds.

Hydrated Compounds

Hydrated compounds are chemicals that incorporate water molecules into their structure. These water molecules are known as 'water of crystallization.' The presence of water affects the appearance and properties of the compound.

Formation and Characteristics:

• Hydrated compounds usually form crystalline solids.
• The water molecules are incorporated into the crystal lattice.
• The amount of water in a hydrate is specific and can be determined by heating and measuring weight loss.
• They have distinct stoichiometry, such as in \(\mathrm{ZnSO}_4 \cdot 7 \mathrm{H}_2\mathrm{O}\).

Hydrated forms often have different solubility and reactivity compared to their anhydrous counterparts. For example, heating hydrates can remove the water, transforming them into their anhydrous forms. This process is typically observed with copper sulfate or magnesium sulfate, which change color when dehydrated.

Common Names in Chemistry

Common names in chemistry often arise from historical contexts or practical usage and can differ from systematic nomenclature. These names help chemists quickly identify compounds without confusion.

Examples and Significance:

• "White vitriol" refers to zinc sulfate heptahydrate and reflects its appearance and historical significance in alchemy.
• "Epsom salt" is another name for magnesium sulfate heptahydrate, widely used for baths and wellness purposes.
• "Glauber's salt" is the name for sodium sulfate decahydrate, recognized from its use in glassmaking and detergent production.

Mastering common names is crucial for students as it links the academic study of chemistry with real-world applications. Although systematic names convey precision, common names carry traditional significance and help in informal communication among chemists.