Expert: Sherman D. - 1/18/2004

Question
Hello my name is Elizabeth.  I am a 17 year old junior in a regular Chemistry 1 class at Winter Park High School and am having a bit of trouble understanding the mole problems.  I was wondering if you could help me some on the questions like...

How many moles is each of the following?
a. 1.50 x 10 to the 23rd molecules NH with a subscript of 3(sorry not sure how to write that out on the keyboard)
b.6.02 x 10 to the 22nd molecules Br with a subscript of 2

Also...I am not sure how you do this problem
Calculate the gram formula mass of each of these substances
a.H(subscript of 3)PO(subscript of 4)
b.N(subscript of 2)O(subscript of 3)

Thanks so much and I'm sorry that it's so hard to understand!

Answer
SInce it has been awhile since i have done this, i am hoping i am doing it correctly.

First question

a.)
1 mole = 6.022 x 10^23 molecules
(1.50 * 10^23)/(6.022 * 10^23)
(1.5/6.022) * 10^(23 - 23)
(1500/6022)
.249086682 or 2.49 * 10^-1 molecules

b.)
(6.02 * 10^22)/(6.022 * 10^23)
(6.02/6.022) * 10^(22 - 23)
(6020/6022) * 10^-1
.99966788 or 1.0 * 10^-1 molecules

2nd Question

a.)
H3 = 1.008 * 3 = 3.024 g/mol
P = 30.974 g/mol
O4 = 63.998 g/mol
so
H3PO4 = 97.995 g/mol

b.)
N2 = 28.013 g/mol
O3 = 47.998
N2O3 = 76.012 g/mol

http://defoort.free.fr/molecalc/ or a Molecular Weight calculator. At this site, you can just type in N2O3 click calculate, then click H3PO4 click calculate.