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# How many hydrogen atoms equal one kilogram in mass?

Can someone please help me? I don't understand Physics at all. I have no idea what to do, since I'm in AP Physics, (I didn't take any previous Physics class, nor did I take biology or chemistry, so I'm unfamiliar with those). I have a 32 right now and it's a long story as tot what happened. So could anyone please help me and explain their answer to me? Because I need to show my work. Thank you very much, I really appreciate it. :D

### 2 Answers

- ElizabethLv 79 years agoFavorite Answer
Hydrogen has a standard atomic weight of ~ 1.008 u. This number is the average based on the abundances of the different isotopes of hydrogen so we'll round that down to exactly 1, which also represents the mass of the most common isotope (ie a single proton).

1u is 1/12th the mass of Carbon-12, and is equivalent to 1.660538921 x 10^-27 kg.

Therefore in one kilogram you would have 1 / 1.66x10^-27 atoms or 6.02 x 10^26 atoms.

This is my physics way of doing it ... a more chemistry way of doing it would be:

The atomic weight of hydrogen is 1. Therefore 1 mol of hydrogen will be 6.02 x 10^23 atoms (Avogadro's Number) and will have a mass of 1 gram. In 1 kilogram I will have 1000 grams and one thousand times the number of hydrogen atoms so:

6.02 x 10^23 x 1000 = 6.02x10^26 atoms (as above).

Just to say, Kuiperbelts answer above is absolutely correct. The only difference is that I deliberately rounded the 1.660538921 x 10^-27 figure to 1.66 rather than his 1.67 to 'force' the result to look like Avogadro's number to show you the 'mol' way of doing it. But 5.99 x 10^26 and 6.02 x 10^26 are, basically, the same number given the rounding we're doing!

- kuiperbelt2003Lv 79 years ago
1 hydrogen atom has a mass of 1.67x10^-27kg

therefore, no. atoms in 1 kg = 1 kg/ 1.67x10^-27kg/atom = 5.99x10^26 atoms