Molecules, Atoms Mass stoichiometry Help!?

Question

Ahh, I'm havig the hardest time on my homework. Please help me. I just dont want the answers please tell me how you did it!

1. AMmonia has the chemical formula NH^3. Suppoose you have 3.0 moles of ammonia.

a) how many molecules of NH^3 are in 3.0 moles of ammonia
b) how many atoms of H are in 3.0 moles of ammonia
c) what is the mass of 3.0 moles of ammonia in grams

Answer 1

you're having difficulty because you are thinking "chemistry"

actually this problem is basic mathematics...

concept of ratio and proportion or dimensional analysis:

take this analogy:



1 dozen = 12 pieces

assuming 1 dozen weighs 24 grams

therefore 12 pieces weigh 24 grams....


now for NH3

1 mole = 17 grams
1 mole = 6.02 x 10 E 23 molecules

therefore 17 grams = 6.02 x 10 E 23 NH3 molecules

so the unit MOLE...bridges these two values together..


NH3 is a combination of 4 atoms:

1 mole NH3 has 1 mole N
1 mole NH3 has 3 mole H

you can use these ratios in calculations...

1 mole N = 14 g
1 mole N = 6.02 x 10 E 23 N atoms

1 mole H = 1 g
1mole H =6.02 x 10 E 23 H atoms


now if i ask you how many dozen do you have if you have

48 pieces.....

or how many dozen is 72 grams


or how many people are there if there are 50 pairs of hands..

how may pieces of gloves will you need for 100 people


if you can answer these...

you can easily answer any stoichiometry problems!!!!


Good luck!!!!

Answer 2

a. 3 x Avogadro's number
b. 3 x 3 x Avogadro's number
3. 3 x 17