if 30gm sample of a chloroplatinate salt of diacidic organic Lewis base on ignition produce 5 gm of white residue, then what will be the molar mass of the base? [Pt = 195]

Options

A. 760
B. 380
C. 1170
D. 410

Answer

To find the molar mass of the diacidic organic Lewis base from the given information, we can follow these steps:

### Step 1: Understand the Composition of the Chloroplatinate Salt
The chloroplatinate salt of the diacidic organic Lewis base is represented as \( B_2H_2PtCl_6 \). This indicates that for every molecule of this salt, there are 2 moles of the base (B).

### Step 2: Determine the Mass Loss During Ignition
When the chloroplatinate salt is ignited, it produces a white residue. The initial mass of the sample is 30 grams, and the mass of the residue after ignition is 5 grams. The mass lost during ignition can be calculated as follows:
\[ \text{Mass lost} = \text{Initial mass} - \text{Residue mass} = 30 \, \text{g} - 5 \, \text{g} = 25 \, \text{g} \]

### Step 3: Identify the Mass of Platinum in the Sample
Since the white residue is primarily platinum, we can conclude that the mass of platinum lost during ignition is equal to the mass lost:
\[ \text{Mass of Pt} = 25 \, \text{g} \]

### Step 4: Calculate the Moles of Platinum
Using the molar mass of platinum (Pt = 195 g/mol), we can calculate the number of moles of platinum produced:
\[ \text{Moles of Pt} = \frac{\text{Mass of Pt}}{\text{Molar mass of Pt}} = \frac{25 \, \text{g}}{195 \, \text{g/mol}} \approx 0.1282 \, \text{mol} \]

### Step 5: Relate Moles of Platinum to Moles of the Sample
From the formula \( B_2H_2PtCl_6 \), we see that there are 2 moles of platinum for every mole of the chloroplatinate salt. Therefore, the moles of the sample can be calculated as:
\[ \text{Moles of sample} = \frac{\text{Moles of Pt}}{2} = \frac{0.1282 \, \text{mol}}{2} \approx 0.0641 \, \text{mol} \]

### Step 6: Calculate the Molar Mass of the Sample
Now, we can find the molar mass of the chloroplatinate salt using the initial mass of the sample:
\[ \text{Molar mass of sample} = \frac{\text{Mass of sample}}{\text{Moles of sample}} = \frac{30 \, \text{g}}{0.0641 \, \text{mol}} \approx 468.5 \, \text{g/mol} \]

### Step 7: Determine the Molar Mass of the Base
Since the formula of the chloroplatinate salt is \( B_2H_2PtCl_6 \), we can express the molar mass of the base (B) as follows:
\[ \text{Molar mass of base} = \frac{\text{Molar mass of sample} - \text{Molar mass of Pt} - \text{Molar mass of Cl}}{2} \]
The molar mass of chlorine (Cl) is approximately 35.5 g/mol, and there are 6 chlorine atoms:
\[ \text{Molar mass of Cl} = 6 \times 35.5 \, \text{g/mol} = 213 \, \text{g/mol} \]
Now substituting the values:
\[ \text{Molar mass of base} = \frac{468.5 \, \text{g/mol} - 195 \, \text{g/mol} - 213 \, \text{g/mol}}{2} = \frac{60.5 \, \text{g/mol}}{2} = 30.25 \, \text{g/mol} \]

### Final Answer
The molar mass of the diacidic organic Lewis base is approximately **30.25 g/mol**.