An organic compound has 68.327% C, 6.406% H, 25.267% CI. Calculate the molecular formula of the compound if its vapour density is 70.25.

Answer

To find the molecular formula of the organic compound with the given percentage composition and vapor density, we will follow these steps:

### Step 1: Determine the Moles of Each Element
We will first convert the percentage composition of each element into moles by dividing the percentage by the atomic mass of each element.

- **Carbon (C)**:
- Percentage = 68.327%
- Atomic mass = 12 g/mol
- Moles of C = 68.327 / 12 = 5.694

- **Hydrogen (H)**:
- Percentage = 6.406%
- Atomic mass = 1 g/mol
- Moles of H = 6.406 / 1 = 6.406

- **Chlorine (Cl)**:
- Percentage = 25.267%
- Atomic mass = 35.5 g/mol
- Moles of Cl = 25.267 / 35.5 = 0.712

### Step 2: Find the Simplest Mole Ratio
Next, we will find the simplest ratio of the moles calculated above by dividing each value by the smallest number of moles obtained.

- Smallest number of moles = 0.712 (for Cl)

- Ratio for C = 5.694 / 0.712 = 8.00
- Ratio for H = 6.406 / 0.712 = 9.00
- Ratio for Cl = 0.712 / 0.712 = 1.00

Thus, the simplest mole ratio is approximately:
- C: 8
- H: 9
- Cl: 1

### Step 3: Write the Empirical Formula
From the mole ratios, we can write the empirical formula:
- Empirical formula = C8H9Cl

### Step 4: Calculate the Empirical Formula Mass
Now, we will calculate the mass of the empirical formula:
- Mass of C8H9Cl = (8 * 12) + (9 * 1) + (1 * 35.5)
- = 96 + 9 + 35.5
- = 140.5 g/mol

### Step 5: Calculate the Molecular Mass
The molecular mass can be calculated using the vapor density:
- Molecular mass = 2 * vapor density
- Given vapor density = 70.25
- Molecular mass = 2 * 70.25 = 140.5 g/mol

### Step 6: Determine the Molecular Formula
To find the molecular formula, we divide the molecular mass by the empirical formula mass:
- n = Molecular mass / Empirical formula mass
- n = 140.5 / 140.5 = 1

Since n = 1, the molecular formula is the same as the empirical formula:
- Molecular formula = C8H9Cl

### Final Answer
The molecular formula of the compound is **C8H9Cl**.

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