The formula of alum is

Options

A. `Al_(2) (SO_(4))_(3)*5H_(2)O`
B. `Al_(2)(SO_(4))_(3)*24H_(2)O`
C. `Al_(2)(SO_(4))_(2)*6H_(2)O`
D. `Al_(2)(SO_(4))_(3)*K_(2)SO_(4)*24H_(2)O`

Answer

To determine the formula of alum, we can follow these steps:

### Step 1: Understanding the Composition of Alum
Alum is a type of chemical compound that typically consists of a double sulfate salt. It is generally represented by the formula M2SO4·M'2(SO4)·24H2O, where M represents a monovalent cation and M' represents a trivalent cation.

### Step 2: Identifying the Cations
In the case of common alums, M is usually a monovalent cation such as potassium (K+) or sodium (Na+), and M' is a trivalent cation such as aluminum (Al3+).

### Step 3: Writing the General Formula
Based on the composition, the general formula of alum can be written as:
\[ \text{M}_2\text{SO}_4 \cdot \text{M'}_2(\text{SO}_4)_3 \cdot 24\text{H}_2\text{O} \]

### Step 4: Example of a Specific Alum
For example, if we take potassium alum, the formula would be:
\[ \text{K}_2\text{SO}_4 \cdot \text{Al}_2(\text{SO}_4)_3 \cdot 24\text{H}_2\text{O} \]
This can be simplified to:
\[ \text{KAl(SO}_4\text{)}_2 \cdot 12\text{H}_2\text{O} \]

### Step 5: Conclusion
Thus, the formula of alum can be represented as:
\[ \text{M}_2\text{SO}_4 \cdot \text{M'}_2(\text{SO}_4)_3 \cdot 24\text{H}_2\text{O} \]
For potassium alum specifically, it is:
\[ \text{KAl(SO}_4\text{)}_2 \cdot 12\text{H}_2\text{O} \]