How many grams of NaOH will be required to neutralise 12.2 g benzoic acid ?

Options

A. 12.2 g
B. 16 g
C. 40 g
D. 4 g

Explanation

To determine how many grams of NaOH are required to neutralize 12.2 g of benzoic acid (C6H5COOH), we can follow these steps:

### Step 1: Write the balanced chemical equation
The neutralization reaction between benzoic acid and sodium hydroxide (NaOH) can be represented as:

\[ \text{C}_6\text{H}_5\text{COOH} + \text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{COONa} + \text{H}_2\text{O} \]

### Step 2: Calculate the molar mass of benzoic acid
To find the molar mass of benzoic acid (C6H5COOH):

- Carbon (C): 12 g/mol × 7 = 84 g/mol
- Hydrogen (H): 1 g/mol × 6 = 6 g/mol
- Oxygen (O): 16 g/mol × 2 = 32 g/mol

Adding these together:

\[ 84 + 6 + 32 = 122 \, \text{g/mol} \]

### Step 3: Calculate the number of moles of benzoic acid
Using the formula:

\[ \text{Moles} = \frac{\text{Given mass}}{\text{Molar mass}} \]

For benzoic acid:

\[ \text{Moles of C}_6\text{H}_5\text{COOH =} \frac{12.2 \, \text{g}}{122 \, \text{g/mol}} = 0.1 \, \text{moles} \]

### Step 4: Determine the moles of NaOH required
From the balanced equation, we see that 1 mole of benzoic acid reacts with 1 mole of NaOH. Therefore, the moles of NaOH required will also be 0.1 moles.

### Step 5: Calculate the molar mass of NaOH
To find the molar mass of NaOH:

- Sodium (Na): 23 g/mol
- Oxygen (O): 16 g/mol
- Hydrogen (H): 1 g/mol

Adding these together:

\[ 23 + 16 + 1 = 40 \, \text{g/mol} \]

### Step 6: Calculate the mass of NaOH required
Using the formula:

\[ \text{Mass} = \text{Moles} \times \text{Molar mass} \]

For NaOH:

\[ \text{Mass of NaOH} = 0.1 \, \text{moles} \times 40 \, \text{g/mol} = 4 \, \text{g} \]

### Final Answer
The mass of NaOH required to neutralize 12.2 g of benzoic acid is **4 grams**.

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