stoichiometry help?

Question

i need help with this topic. i'm kinda new to this one. pls show some working as well so that i can learn from there thks.


1) how many moles are there in 8 grams of hydrogen gas?
2)how many moles are there in 8 grams of bromine liquid?
3)how many grams of neon have the same number of atoms as 8 grams of oxygen?


thanks alot!

Answer 1

According to avogadro's law there are 6.023*10^23 particle in a mole of a substance.
1 mole of a compound/element contains 6.023*10^23 units of it.
The mass of 1 mole of the substance is equal to its molecular weight in gram.
example molecular mass of H2 is 2(2 molecules of H each of atomic mass 1). So mass of 1 mole of H2 is 2 grams.
Similarly mass of 1 mole Oxygen gas is 32 grams(2 atoms of atomic mass 16 gram each).

Also 1 mole of gas occupies 22.4 litres volume at STP

Now your answers

1)
8 grams of hydrogen means 4 moles of hydrogen.
Number of moles= mass of substance(in grams) / gram molecular mass.

2)Bromine molecular mass=2*80=160 grams
so number of moles =8/160= 0.05 moles

3) 8 gram oxygen(O2) has 0.25 moles
mass of .25 moles of neon=0.25*8(molecular mass of Ne)
=2 grams

Answer 2

(1) 8g H2 X (1mol/2g per mol) = 4 moles
(2) 8g Br X (1mol/80g per mol) = 0.1 mole

Answer 3

Ah... let me go review my chemistry, and I'll get back with you.