Final answer:
To find the mass of a 10.2 mL sample of H₂ at STP, calculate the number of moles using the molar volume at STP and multiply it by the molar mass of hydrogen, resulting in approximately 0.000918 grams or 0.00092 g when rounded.
Step-by-step explanation:
To determine the mass of a 10.2 mL sample of H₂ at STP (standard temperature and pressure), we need to use the ideal gas law and the molar mass of hydrogen. At STP, one mole of any gas occupies 22.4 liters. Therefore, to find the number of moles in 10.2 mL of hydrogen gas, we divide the volume of the gas by the molar volume of a gas at STP:
Number of moles = (10.2 mL) / (22,400 mL/mol) = 0.0004554 mol
The next step is to calculate the mass of this number of moles. The molar mass of H₂ is approximately 2.016 g/mol. Thus, we multiply the number of moles by the molar mass of hydrogen to find the mass:
Mass of H₂ = 0.0004554 mol × 2.016 g/mol = 0.00091792 g
Converting this into grams gives the final answer:
Mass of 10.2 mL of H₂ at STP = 0.000918 g ≈ 0.00092 g (rounded to five significant figures)