What is the total number of hydrogen atoms in 0.300 mol of hydrazine, N2H4? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct answer
A. 7.22 × 10^23
Principle or equation
The number of atoms of a specific element in a sample is obtained by multiplying the amount of substance (in moles) by the number of atoms of that element per formula unit and then by Avogadro's constant.
Why this answer is correct
Each molecule of N2H4 contains 4 hydrogen atoms. Therefore, moles of H atoms = 0.300 mol × 4 = 1.20 mol. Number of H atoms = 1.20 mol × 6.02 × 10^23 mol^-1 = 7.224 × 10^23, which rounds to 7.22 × 10^23.
Example
For 0.500 mol of H2O, the number of H atoms = 0.500 × 2 × 6.02 × 10^23 = 6.02 × 10^23.
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