The molarity of the solution containing 2.8% (mass/volume) solution of KOH is: (Given atomic mass of K=39) is:

Options

A. `0.1M`
B. `0.5M`
C. `0.2M`
D. `1M`

Explanation

To find the molarity of a 2.8% (mass/volume) solution of KOH, we can follow these steps:

### Step 1: Understand the given percentage
A 2.8% (mass/volume) solution means that there are 2.8 grams of KOH in 100 mL of solution.

### Step 2: Calculate the molar mass of KOH
The molar mass of KOH can be calculated by adding the atomic masses of its constituent elements:
- Atomic mass of Potassium (K) = 39 g/mol
- Atomic mass of Oxygen (O) = 16 g/mol
- Atomic mass of Hydrogen (H) = 1 g/mol

Thus, the molar mass of KOH = 39 + 16 + 1 = 56 g/mol.

### Step 3: Calculate the number of moles of KOH
To find the number of moles of KOH, we use the formula:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]
Substituting the values:
\[ \text{Number of moles} = \frac{2.8 \text{ g}}{56 \text{ g/mol}} = 0.05 \text{ moles} \]

### Step 4: Convert the volume of the solution to liters
The volume of the solution is given as 100 mL. To convert this to liters:
\[ \text{Volume in liters} = \frac{100 \text{ mL}}{1000} = 0.1 \text{ L} \]

### Step 5: Calculate the molarity of the solution
Molarity (M) is defined as the number of moles of solute per liter of solution:
\[ \text{Molarity} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \]
Substituting the values we calculated:
\[ \text{Molarity} = \frac{0.05 \text{ moles}}{0.1 \text{ L}} = 0.5 \text{ M} \]

### Final Answer
The molarity of the solution is **0.5 M**.

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