How many moles of hydrogen will weigh 1 kg?

The atomic mass of hydrogen is 1 g/mole. To make up 1 kilogram or 1000 g of hydrogen element, 1000 moles of hydrogen is required. Each mole has a Avogadro's number of atoms or `6.023 xx 10^(23)`  atoms. Thus, 1 kg hydrogen element or 1000 moles of hydrogen have `6.023 xx 10^(26)` atoms (or 1000 times the Avogadro's number). 

Hydrogen gas, unlike hydrogen atom, is made up of 2 atoms of hydrogen. Molecules of hydrogen gas are represented as `H_2` .  The molecular mass of hydrogen gas is 2 g/mole. To make up for 1 kg hydrogen or 1000 gm of hydrogen gas, we need 500 moles of hydrogen gas. These many moles of hydrogen gas will have `3.011 xx 10^26` atoms (500 times the Avogadro's number of atoms). 

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