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JAMB Chemistry 2012 Paper

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Question : 2

Total: 45

How many atoms are present in 6.0g of magnesium?

[Mg = 24, N_A = 6.02 x 10²³ mol^-1]

1.20 x 10²²
2.41 x 10²²
1.51 x 10²³
3.02 x 10²³

Solution:

Concept:

Number of atoms = moles

\times

Avogadro's constant.

Explanation:

Moles of magnesium =

\frac{\text{mass}}{\text{molar mass}} = \frac{6.0}{24} = 0.25

mol.

Number of atoms =

0.25 \times 6.02 \times 10^{23}

.

Number of atoms =

1.505 \times 10^{23}

.

Rounded appropriately:

1.51 \times 10^{23}

atoms.

Answer:

1.51 \times 10^{23}

atoms, i.e. option C.

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