Problem 78 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is arranged in order of decreasing solubility in water? (a) \(\mathrm{CaSO}_{4}>\mathrm{BaSO}_{4}>\mathrm{BeSO}_{4}>\mathrm{MgSO}_{4}>\mathrm{SrSO}_{4}\) (b) \(\mathrm{BeSO}_{4}>\mathrm{MgSO}_{4}>\mathrm{CaSO}_{4}>\mathrm{SrSO}_{4}>\mathrm{BaSO}_{4}\) (c) \(\mathrm{BaSO}_{4}>\mathrm{SrSO}_{4}>\mathrm{CaSO}_{4}>\mathrm{MgSO}_{4}>\mathrm{BeSO}_{4}\) (d) \(\mathrm{BeSO}_{4}>\mathrm{CaSO}_{4}>\mathrm{MgSO}_{4}>\mathrm{SrSO}_{4}>\mathrm{BaSO}_{4}\)

Step-by-Step Solution

Answer

The correct order is (b) \( \text{BeSO}_4 > \text{MgSO}_4 > \text{CaSO}_4 > \text{SrSO}_4 > \text{BaSO}_4 \).

Step 1: Understanding Solubility Trends

Beryllium sulfate, \( \text{BeSO}_4 \), is quite soluble in water, while barium sulfate, \( \text{BaSO}_4 \), is not. Solubility generally decreases as you go down Group 2 in the periodic table. Therefore, the order is most likely decreasing from Be to Ba.

Step 2: Checking Each Option

Examine each option to see if it follows the expected trend: - Option (a): \( \text{CaSO}_4 > \text{BaSO}_4 > \text{BeSO}_4 > \text{MgSO}_4 > \text{SrSO}_4 \) - does not follow the trend.- Option (b): \( \text{BeSO}_4 > \text{MgSO}_4 > \text{CaSO}_4 > \text{SrSO}_4 > \text{BaSO}_4 \) - follows the expected trend of decreasing solubility.- Option (c): \( \text{BaSO}_4 > \text{SrSO}_4 > \text{CaSO}_4 > \text{MgSO}_4 > \text{BeSO}_4 \) - reverse order.- Option (d): \( \text{BeSO}_4 > \text{CaSO}_4 > \text{MgSO}_4 > \text{SrSO}_4 > \text{BaSO}_4 \) - similar to option (b), but \( \text{CaSO}_4 \) should come after \( \text{MgSO}_4 \).

Step 3: Final Comparison and Conclusion

Option (b) correctly shows the decreasing order of solubility from Be through Ba. The trend is consistent with known solubility patterns for sulfates of Group 2 elements.

Key Concepts

Group 2 Chemistry

Group 2 elements in the periodic table are also known as alkaline earth metals. This group includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). These metals share some common characteristics due to their similar electron configurations. Each of these elements has two electrons in their outermost shell, which contributes to their reactivity.

Their reactivity tends to increase as you move down the group. This is because outer electrons are further from the nucleus and more loosely held, making it easier for the atoms to participate in reactions. Additionally, the oxides and hydroxides of these elements typically form alkaline solutions when dissolved in water.

The chemistries of Group 2 elements are crucial in understanding their solubility trends, especially when they form compounds like sulfates. Their relatively low electronegativities and larger atomic sizes compared to other groups result in unique solubility behaviors, as seen with their sulfate compounds.

Sulfate Solubility

The solubility of sulfate compounds of Group 2 elements in water is a fascinating trend in chemistry. Solubility refers to the ability of a substance to dissolve in a solvent, forming a solution, and here we focus on water as the solvent.

For the sulfates in Group 2, there's a distinctive pattern: the solubility decreases as you move down the group from BeSO o 4 o to BaSO o 4 o.

• Beryllium sulfate (BeSO_4) is highly soluble in water, meaning it dissolves easily.
• Magnesium sulfate (MgSO_4) is also quite soluble and commonly encountered as Epsom salt, found in health and beauty products.
• However, when we reach calcium sulfate (CaSO_4), the solubility becomes significantly lower. This is commonly seen as gypsum, a material used in construction.
• Strontium sulfate (SrSO_4) and barium sulfate (BaSO_4) have even lower solubility, with barium sulfate being almost insoluble in water, making it an excellent choice for medical imaging.

This decreasing trend in solubility is crucial for predicting chemical behaviors and selecting materials for specific applications.

Periodic Table Trends

Periodic table trends are essential for predicting the chemical behaviors of elements. One important trend observed in the periodic table is the variation in solubility of compounds as you move across or down a group.

For Group 2 elements, the trend shows that as you move from top to bottom, the solubility of their sulfates in water decreases. Here are a few reasons behind this trend:

• As you descend the group, ionic sizes increase. Larger ions form weaker attractions with water molecules, reducing solubility.
• The lattice energy, which is the energy needed to separate ions in an ionic compound, becomes more significant compared to hydration energy as we go down the group. This makes compounds like BaSO_4 less soluble.

Understanding these periodic table trends helps chemists and students predict and explain the behavior of elements and their compounds. It provides a logical framework that simplifies complex chemistry concepts into more digestible pieces of information.