Question

A flask contains 98 mg of H₂SO₄. If \( 3.01 \times 10^{20} \) molecules of H₂SO₄ are removed from the flask, the number of moles of H₂SO₄ remaining in the flask is (\( N = 6.02 \times 10^{23} \)):

• A. \( 1 \times 10^{-4} \)
• B. \( 5 \times 10^{-4} \)
• C. \( 1.66 \times 10^{-3} \)
• D. \( 9.95 \times 10^{-3} \)

Hint:

To find remaining moles, subtract removed moles from initial moles using Avogadro’s number.

Answer 1

The Correct Option is B

Step 1: Compute Initial Moles of H₂SO₄ \[ \text{Moles of H₂SO₄} = \frac{\text{Mass}}{\text{Molar mass}} = \frac{98 \times 10^{-3}}{98} = 10^{-3} \text{ moles} \] Step 2: Convert Removed Molecules to Moles \[ \text{Moles removed} = \frac{3.01 \times 10^{20}}{6.02 \times 10^{23}} \] \[ = 5 \times 10^{-4} \text{ moles} \] Step 3: Compute Remaining Moles \[ \text{Remaining moles} = (10^{-3} - 5 \times 10^{-4}) \] \[ = 5 \times 10^{-4} \text{ moles} \] Thus, the correct answer is \( 5 \times 10^{-4} \).

Answer 2

Step 1: Calculate Initial Moles of H₂SO₄
\[ \text{Moles of H₂SO₄} = \frac{\text{Mass}}{\text{Molar mass}} = \frac{98 \times 10^{-3} \text{ g}}{98 \text{ g/mol}} = 10^{-3} \text{ moles} \]
Step 2: Convert Number of Removed Molecules to Moles
\[ \text{Moles removed} = \frac{3.01 \times 10^{20}}{6.02 \times 10^{23}} = 5 \times 10^{-4} \text{ moles} \]
Step 3: Calculate Remaining Moles of H₂SO₄
\[ \text{Remaining moles} = 10^{-3} - 5 \times 10^{-4} = 5 \times 10^{-4} \text{ moles} \]
Final Result:
The amount of H₂SO₄ remaining after removing the specified molecules is \( 5 \times 10^{-4} \) moles.