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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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ilibee ilibee
wrote...
11 years ago
Can you please explain how to do this??

Determine the number of moles of compound in each of the following samples;
a. 4.50g H2O
b. 129.68g Fe3(PO4)2
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wrote...
#1
11 years ago
One mole is defined as the amount of a substance so that its mass is equal to its formula weight:

Moles = mass / FW.

So simply determine the formula weights for each compound (from the periodic table), and divide the mass in the sample by the formula weight.
wrote...
#2
11 years ago
Atomic mass is found from the Periodic Table of Elements.
a...Mol. mass of H2O = 18g/mole. (H.1x2) + (O.16x 1)
Moles = Mass/Mol.mass =  4.5g/18g/mol. = 0.25 moles H2O.

b...Mol. mass of Fe3(PO4)2..
= (Fe.56 x 3) + (P.31 x 2) + (O.16 x 8) = 168 + 62 + 128 = 358g/mol.
129.68g/358/g/mol. = 0.362 moles Fe3(PO4)2
wrote...
#3
11 years ago
General formula: m=nM where m is the mass, n is the no. of mol, and M is th molar mass.

a. n(H2O)= m/M = 4.5/18=.....................
b. n(Fe3(PO4)2)= 129.68/ the molar mass.

u get the molar masses from the periodic table. How?? eg:

M (H2O)= 2xM(H) + M(O) = 2(1)+16= 18 g/mol
wrote...
#4
11 years ago
a...Mol. mass of H2O = 18g/mole.
Moles = Mass/Mol.mass = 4.5g/18g/mol. = 0.25 moles H2O.

b...Mol. mass of Fe3(PO4)2..
= (56 x 3) + (31 x 2) + (16 x 8) = 168 + 62 + 128 = 358g/mol.
129.68g/358/g/mol. = 0.362 moles Fe3(PO4)2

please chose me for best i really need it
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