1) For the first problem, you start by looking at HNO3 and because they tell you that HNO3 is consumed, you know that this is leading the reaction.
Take HNO3 convert the grams you have been given to moles and then you can follow the stoichiometry to know what will be yielded.
to convert to moles use dimensional analysis and the atomic weights or masses you have been given here in the problem.
1 H = 1
1 N= 14
3 O = 16 x3= 48
atomic. weight for HNO3 = 63g/mol
using these units convert to moles
___________ X ________
grams cancel out and you have 0.8351 mol-1, but you will have to take the inverse to get this to just moles. so by doing 1/0.8351 this will give you the exact moles of 1.197 moles.
Then look at equation given in problem, is the equation balanced?
S + 6 HNO3 --> H2SO4 + 6 NO2 + 2 H2O
6 Hydrogens on both sides
6 Nitrogens on both sides
18 Oxygens on both sides
1 Sulfur on both sides
you have a balanced equation
So go according to the balanced equation use the coeffecients in front of each species on the reactant and product side:
If 6 moles HNO3 ------> 2 moles H20,
then 1.197 moles HNO3 -----> X moles H20
cross multiply and divide,
6X = 2(1.197)
X = 2(1.197)
X = 2.394
X= 0.399 = 0.4 moles of water, H2O when rounding to the nearest tenths place
So you will get 0.4 moles of water, H2O from 1.197 moles of HNO3, which you received from 163.6g of the molecule/acid HNO3.
2) You use the same concept and process for this problem as well:
convert your grams to moles of the nitric acid HNO3 here we have it at 118.6 g of HNO3
the atomic weight of HNO3 is still: 63g see above for how it was derived
now taking the 118.6 g
1/118.6g x 63g/mol = 0.53119 mol-1, so you still have to take the inverse because moles is on bottom,
so 1/0.53119 = 1.8825 moles of HNO3
Now using this balanced equation, find out how many moles of water H2O can be yielded:
3 Cu + 8HNO3 --> 3 Cu(NO3)2 + 2 NO + 4 H2O
If 8 moles of HNO3 -------> 4 moles of H2O
then 1.8825 moles HNO3------> X moles of H2O
Cross multiply divide and solve for X
X = 0.94125 = 1.0 moles when rounded to the tenths place. This is your moles of water produced or yielded from this reaction with your HNO3 being 1.8825 moles and 118.6 g of the HNO3.