Problem 21 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Molecular formula of Glauber's salt is : (a) \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{FeSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The molecular formula of Glauber's salt is \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\), which is option (d).

Step 1: Identifying Compound Name

Glauber's salt is a common name in chemistry. It refers to a specific hydrated form of sodium sulfate.

Step 2: Understanding Hydrates

In chemistry, a hydrate is a compound that includes water molecules within its crystalline structure. Glauber's salt is known to contain water of crystallization.

Step 3: Analyzing the Options

Now, let's look at the options given:(a) \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) is Epsom salt.(b) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) is Blue Vitriol.(c) \(\mathrm{FeSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) is Green Vitriol.(d) \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\) is Glauber's salt.

Step 4: Choosing the Correct Formula

From the analysis, we identified that Glauber's salt corresponds to option (d), which is \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\).

Key Concepts

Molecular Formula

The molecular formula is a way chemists express information about the atoms that make up a particular molecule. It tells us not just what elements are present in the compound, but also the number of each type of atom. For Glauber's salt, the molecular formula is \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\).

This formula reveals that the compound contains:

• Two sodium (Na) atoms
• One sulfur (S) atom
• Four oxygen (O) atoms within the sulfate ion \(\mathrm{SO}_{4}\)
• Ten water molecules \(\mathrm{H}_{2} \mathrm{O}\)

The presence of water molecules here is significant and distinctly alters the properties of the compound compared to its anhydrous (without water) form. Understanding the molecular formula allows scientists and students to derive important chemical characteristics and predict behaviors or reactions the compound may participate in.

Hydrates

Hydrates are compounds that incorporate water molecules directly into their structure. These water molecules are typically not just mixed in with the compound but are part of the crystalline framework itself.

When a hydrate form of a compound is compared to its anhydrous form, several changes can be noted:

• The hydrate often has different physical properties, such as color and solubility.
• The presence of water generally increases the volume of the crystals.
• They can often lose water quite easily, especially upon heating, thus changing their physical state.

The chemistry of hydrates can be further explored by studying how the compound releases its water content. Often, such compounds can become powders or absorb moisture, a process of great industrial importance. Glauber's salt, for instance, can be dehydrated to sodium sulfate, which is then useful in various applications, from detergents to heat storage.

Water of Crystallization

Water of crystallization refers to water molecules that are necessary to maintain the structure of a crystalline compound. The water, in this context, is an integral part of the crystalline network. It helps stabilize the structure by forming weak forces like hydrogen bonds between various components of the compound.

For Glauber's salt, the water of crystallization means that ten molecules of water for every molecule of sodium sulfate are crucial to its structure. The formula \(\mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O}\) denotes these ten water molecules explicitly.

• This built-in water content makes the salt appear moist and contributes to its transparent or white crystalline appearance.
• The water molecules can be driven off by heating, reverting it to an anhydrous form.

Understanding water of crystallization is vital, especially in the chemical industry, because it affects the stability and reactivity of various substances. It's how substances can reversibly absorb moisture, a feature leveraged in desiccants and other chemical applications.