What is the molar mass of diacidic organic Lewis base, if `12 g` of chloroplatinate salt on ignition produced `5 g` residue ?

Options

A. `52`
B. `58`
C. `88`
D. none of these

Explanation

To find the molar mass of the diacidic organic Lewis base, we will follow these steps:

### Step 1: Understand the Problem
We are given that 12 g of a chloroplatinate salt produces a residue of 5 g upon ignition. The chloroplatinate salt is represented as \( BH_2 \cdot PtCl_6 \).

### Step 2: Calculate the Mass of Platinum
The mass of platinum in the residue is given as 5 g. The total mass of the chloroplatinate salt is 12 g, and the mass lost during ignition is \( 12 \, \text{g} - 5 \, \text{g} = 7 \, \text{g} \).

### Step 3: Determine the Molar Mass of Chloroplatinate Salt
We know that the molar mass of platinum (Pt) is approximately 195 g/mol. The amount of platinum in the residue (5 g) can be used to find the total molar mass of the chloroplatinate salt.

Using the ratio of the mass of platinum to the mass of the chloroplatinate salt:
\[ \text{Molar mass of chloroplatinate salt} = \frac{12 \, \text{g}}{5 \, \text{g}} \times 195 \, \text{g/mol} \]
Calculating this gives:
\[ \text{Molar mass of chloroplatinate salt} = \frac{12}{5} \times 195 = 468 \, \text{g/mol} \]

### Step 4: Find the Molar Mass of \( PtCl_6 \)
The molar mass of \( PtCl_6 \) (platinum hexachloride) can be calculated as follows:
- Molar mass of Pt = 195 g/mol
- Molar mass of Cl = 35.5 g/mol
- Molar mass of \( PtCl_6 = 195 + 6 \times 35.5 = 195 + 213 = 408 \, \text{g/mol} \)

### Step 5: Calculate the Molar Mass of the Base \( BH_2 \)
Now we can find the molar mass of the diacidic organic Lewis base \( BH_2 \):
\[ \text{Molar mass of } BH_2 = \text{Molar mass of chloroplatinate salt} - \text{Molar mass of } PtCl_6 \]
Substituting the values:
\[ \text{Molar mass of } BH_2 = 468 \, \text{g/mol} - 408 \, \text{g/mol} = 60 \, \text{g/mol} \]

### Final Answer
The molar mass of the diacidic organic Lewis base \( BH_2 \) is **60 g/mol**.

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