[ericbmd]

How many H atoms are there in 5.40g of Ammonia.

Is this right?
Molar mass of NH3 =14 + 3x1 = 17
No. of moles of NH3 Mass/Molar Mass

5.4g/17 = 0.3176 moles

1Mol of NH3 = 3 x 6.022x 10 23 atoms of H

0.3176 mol of NH3 = 0.3176 x 3 x 6.023x10 23 = 5.738 x 10 23 atoms H. 

[Borek]

Is this right?

No. How many moles of ammonia you have? How many ammonia molecules? How many atoms of hydrogen per ammonia molecule?

[Stewed_ant]

eric, like borek said now, step by step.

You have 5.4 g NH3  and you have moles= (mass) / (molecular mass)  or n=m/M.

----> find the molecular weight of NH3 using a periodic table.
----> find the number of moles of NH3 you have.
----> Now for ever mole of NH3, you have 3 mol of H's.
----> number moles by avocadro's number gives number of H's.