How many electrons per mole of Pt are transferred when aqua regia oxidized platinum?

Options

A. 3
B. 4
C. 5
D. 6

Explanation

To determine how many electrons per mole of platinum (Pt) are transferred when aqua regia oxidizes platinum, we can follow these steps:

### Step 1: Write the balanced chemical equation
Aqua regia is a mixture of hydrochloric acid (HCl) and nitric acid (HNO3) that can oxidize platinum. The reaction can be represented as:
\[ \text{Pt} + 6 \text{HCl} + 4 \text{HNO}_3 \rightarrow \text{H}_2\text{PtCl}_6 + 4 \text{NO} + 2 \text{H}_2\text{O} \]

### Step 2: Identify the oxidation states
In the reaction, platinum (Pt) starts with an oxidation state of 0 (elemental state). In the product \(\text{H}_2\text{PtCl}_6\), we need to determine the oxidation state of Pt.

### Step 3: Calculate the oxidation state of Pt in \(\text{H}_2\text{PtCl}_6\)
Let the oxidation state of Pt be \(x\).
- The oxidation state of H is +1 (2 H gives +2).
- The oxidation state of Cl is -1 (6 Cl gives -6).

Setting up the equation for the neutral compound:
\[ x + 2 + (-6) = 0 \]
\[ x - 4 = 0 \]
\[ x = +4 \]

### Step 4: Determine the change in oxidation state
The change in oxidation state for Pt is from 0 to +4. This means that Pt loses 4 electrons during the oxidation process.

### Step 5: Calculate the number of electrons transferred per mole
Since the oxidation state of Pt changes from 0 to +4, the number of electrons transferred per mole of Pt is 4.

### Conclusion
Therefore, when aqua regia oxidizes platinum, **4 electrons per mole of Pt are transferred**.