Final answer:
To find the number of moles of hydrogen atoms in a 3.5 g sample of H2 gas, you divide the mass of H2 by its molar mass and then multiply by 2, because each molecule of H2 has 2 hydrogen atoms. This yields approximately 3.46 moles of hydrogen atoms.
Step-by-step explanation:
To calculate how many moles of hydrogen atoms are in a 3.5 g sample of H2 gas, we must first know the molar mass of H2, which is approximately 2.02 g/mol (each hydrogen atom has an approximate atomic mass of 1.01 g/mol and there are two hydrogen atoms in each molecule). Next, we use the formula for moles:
Moles of H2 = mass of H2 / molar mass of H2
Which gives us:
Moles of H2 = 3.5 g / 2.02 g/mol ≈ 1.73 mol
However, we want the number of moles of hydrogen atoms, not H2 molecules. Since each molecule of H2 contains 2 hydrogen atoms, we multiply the number of moles of H2 by 2:
Moles of hydrogen atoms = 1.73 mol H2 × 2 ≈ 3.46 mol