100 mL of HCI + 35 mL of NaOH, colour of methyl orange in the solution will be

Options

A. red
B. yellow
C. can't be predicted
D. methyl orange is not suitable indicator

Answer

To determine the color of methyl orange in a solution formed by mixing 100 mL of HCl with 35 mL of NaOH, we can follow these steps:

### Step 1: Identify the nature of the reactants
- HCl is a strong acid, and NaOH is a strong base. When they are mixed, they will undergo a neutralization reaction.

### Step 2: Calculate the moles of HCl and NaOH
- Assume the concentration of HCl is 1 M (for simplicity).
- Moles of HCl = Volume (L) × Concentration (M) = 0.1 L × 1 M = 0.1 moles.
- Assume the concentration of NaOH is also 1 M.
- Moles of NaOH = Volume (L) × Concentration (M) = 0.035 L × 1 M = 0.035 moles.

### Step 3: Determine the limiting reagent
- Since there are 0.1 moles of HCl and 0.035 moles of NaOH, NaOH is the limiting reagent.
- After the reaction, moles of HCl remaining = 0.1 - 0.035 = 0.065 moles.

### Step 4: Calculate the final concentration of HCl
- The total volume of the solution after mixing = 100 mL + 35 mL = 135 mL = 0.135 L.
- Final concentration of HCl = Remaining moles / Total volume = 0.065 moles / 0.135 L ≈ 0.481 M.

### Step 5: Determine the pH of the solution
- Since HCl is a strong acid, the pH can be calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
- Here, \([\text{H}^+] = 0.481 M\).
- pH = -log(0.481) ≈ 0.32.

### Step 6: Analyze the pH with respect to methyl orange
- Methyl orange changes color in the pH range of 3.1 (red) to 4.4 (yellow).
- Since the calculated pH (0.32) is less than 3.1, the solution will be in the red color range.

### Conclusion
- The color of methyl orange in the solution will be **red**.

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