`1M HCl and 2 M HCl ` are mixed in volume ratio 4:1. What is the final molarity of HCl solution?

Options

A. 1.5
B. 1
C. 1.2
D. 1.8

Answer

To find the final molarity of the HCl solution when mixing 1M HCl and 2M HCl in a volume ratio of 4:1, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the concentrations and volume ratios:**
- Let the concentration of the first solution (1M HCl) be \( M_1 = 1 \, \text{M} \).
- Let the concentration of the second solution (2M HCl) be \( M_2 = 2 \, \text{M} \).
- The volume ratio of the two solutions is given as 4:1. We can assume:
- Volume of the first solution, \( V_1 = 4x \)
- Volume of the second solution, \( V_2 = x \)

2. **Calculate the total moles of HCl from both solutions:**
- Moles of HCl from the first solution:
\[ \text{Moles from } M_1 = M_1 \times V_1 = 1 \, \text{M} \times 4x = 4x \]
- Moles of HCl from the second solution:
\[ \text{Moles from } M_2 = M_2 \times V_2 = 2 \, \text{M} \times x = 2x \]

3. **Calculate the total moles of HCl:**
- Total moles of HCl:
\[ \text{Total moles} = 4x + 2x = 6x \]

4. **Calculate the total volume of the mixed solution:**
- Total volume:
\[ V_{\text{total}} = V_1 + V_2 = 4x + x = 5x \]

5. **Calculate the final molarity of the mixed solution:**
- Final molarity \( M_f \) can be calculated using the formula:
\[ M_f = \frac{\text{Total moles of HCl}}{\text{Total volume}} = \frac{6x}{5x} \]
- Simplifying this gives:
\[ M_f = \frac{6}{5} = 1.2 \, \text{M} \]

### Final Answer:
The final molarity of the HCl solution is **1.2 M**.

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