Question

A coordination complex contains \(2.6\ \%\) of Mg. Find the number of Mg atoms in \(5.0\) g of this sample.
(gram atomic mass of Mg \(=24\) g )

• A. \(1.5\times 10^{21}\)
• B. \(3.26\times 10^{21}\)
• C. \(2.82\times 10^{21}\)
• D. \(4.3\times 10^{21}\)

Hint:

Find the mass of Mg from the percentage, convert it to moles and then to atoms.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
The number of atoms is moles times Avogadro's number \(6.022\times10^{23}\).

Step 2: Mass of Mg
Mass of Mg \(=\dfrac{2.6}{100}\times5.0=0.13\) g.

Step 3: Moles of Mg
Moles \(=\dfrac{0.13}{24}=5.42\times10^{-3}\) mol.

Step 4: Number of atoms
Atoms \(=5.42\times10^{-3}\times6.022\times10^{23}\approx3.26\times10^{21}\).

Final Answer:
The sample contains about \(3.26\times10^{21}\) Mg atoms. \[ \boxed{\text{(B) }3.26\times10^{21}} \]