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: Understand the formula for molarity
Molarity (M) is defined as the number of moles of solute divided by the volume of the solution in liters.

\[ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{volume of solution in liters}} \]

### Step 2: Calculate the number of moles of NaOH
To find the number of moles of NaOH, we use the formula:

\[ \text{moles of NaOH} = \frac{\text{mass of NaOH (g)}}{\text{molar mass of NaOH (g/mol)}} \]

Given:
- Mass of NaOH = 200 g

Now, we need to find the molar mass of NaOH. The molar mass can be calculated as follows:
- Atomic mass of Sodium (Na) = 23 g/mol
- Atomic mass of Oxygen (O) = 16 g/mol
- Atomic mass of Hydrogen (H) = 1 g/mol

\[ \text{Molar mass of NaOH} = 23 + 16 + 1 = 40 \text{ g/mol} \]

Now, substituting the values into the moles formula:

\[ \text{moles of NaOH} = \frac{200 \text{ g}}{40 \text{ g/mol}} = 5 \text{ moles} \]

### Step 3: Calculate the molarity
Now that we have the number of moles, we can calculate the molarity. The volume of the solution is given as 1 liter.

\[ \text{Molarity (M)} = \frac{5 \text{ moles}}{1 \text{ L}} = 5 \text{ M} \]

### Final Answer
The molarity of the NaOH solution is **5 M**.

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