Tell how many moles of each element are in the following amounts of compounds?

a. 3 moles of NH3


b. 0.25 moles of H2O


c. 5 moles of H2SO4


d. 0.75 moles of Ca(NO3)2





i think i got the right answers but im gettin confused, just a ? wen u have more than 1 mole. say 4 example c. for hydrogen do u add the 2 n the 5 or do u multiply them together

Tell how many moles of each element are in the following amounts of compounds?
Okay,


First, convert moles to grams.


a.


N-14


H-1(3)


NH3-17


3 mole NH3 x [17 gNH3/1mol NH3] = 51 g NH3


--


b.


H-1(2)


O-16


H2O-18


.25 mole H2O x [18g H2O/1mol H2O] = 4.5 g H2O


--


c.


H-1(2)


S-32


O-16(4) = 64


H2SO4 = 98


5 mol H2SO4 x [98 g H2SO4/1mol H2SO4] = 490 g H2SO4


--


d.


Ca-40


[N-14


O-16(3) = 48]


x2 =124


Ca(NO3)2 = 164


.75 mol Ca(NO3)2 x [124 g/1mol] = 93 g Ca(NO3)2


=========


Now, find percent composition.


a.


N-14/17 = 82.4% N


H-1(3)/17 = 17.6%H


NH3-17


b.


H-1(2)/18 = 11.1% H


O-16/18 = 88.9% O


H2O-18


c.


H-1(2)/98 = 2% H


S-32/98 = 32.7% S


O-16(4) = 64/98 =65.3% O


H2SO4 = 98


d.


Ca-40/164 = 24.4%


N-14(2) = 28/164 = 17.1%


O-16(6) = 96/164 = 58.5%


Ca(NO3)2 = 164


=======


Now, use each percent and multiply by the total number of moles to find amount of moles in each substance.


a.


82.4% N x 3 mol = 2.47 mol N


17.6%H x 3 mol = .053 mol H


b.


11.1% H x .25 mol = .028 mol H


88.9% O x .25 mol = .222 mol O


c.


2% H x 5 mol = .10 mol H


32.7% S x 5 mol = 1.64 mol S


65.3% O x 5 mol = 3.27 mol O


d.


24.4% Ca x .75 mol = .183 mol Ca


17.1% N x .75 mol = .128 mol N


58.5% O x .75 mol = .439 mol O





I hope this helps.