A given solution of NaOH contains 200 g of NaOH per litre of solution. Calculate the molarity, of this solution.

Answer

To calculate the molarity of a solution of NaOH that contains 200 g of NaOH per liter, we can follow these steps:

### Step 1: Identify the mass of NaOH
We are given that the mass of NaOH in the solution is 200 grams.

### Step 2: Determine the molar mass of NaOH
The molar mass of NaOH can be calculated as follows:
- Sodium (Na) = 23 g/mol
- Oxygen (O) = 16 g/mol
- Hydrogen (H) = 1 g/mol

Thus, the molar mass of NaOH = 23 + 16 + 1 = 40 g/mol.

### Step 3: Calculate the number of moles of NaOH
Using the formula for moles:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]
Substituting the values:
\[ \text{Number of moles of NaOH} = \frac{200 \text{ g}}{40 \text{ g/mol}} = 5 \text{ moles} \]

### Step 4: Calculate the molarity of the solution
Molarity (M) is defined as the number of moles of solute per liter of solution:
\[ \text{Molarity (M)} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \]
Here, the volume of the solution is 1 liter. Thus:
\[ \text{Molarity} = \frac{5 \text{ moles}}{1 \text{ L}} = 5 \text{ M} \]

### Final Answer
The molarity of the NaOH solution is **5 M (moles per liter)**.

---