How do you find # of atoms of nitrogen in this compound?

Question

How many atoms of Nitrogen in 5 grams of Mg3N2?

I'm not sure if I'm doing these type of problems right.

I''m doing (1/28)*(5)*(6.02E23) but i really don't remember how you're supposed to do it. =/

Answer 1

First work out the number of moles of Mg3N2 in 5 g

moles = mass / molecular weight

molecular weight = (3 x 24.31) + (2 x 14.01)

= 100.95 g/mol

So moles = 5 g / 100.95 g/mol

= 0.04953 moles

Now look at your formula. 1 molecule of Mg3N2 has 2 atoms of N, therefore in 0.04953 moles of Mg3N2 there will be (2 x 0.04953) moles of N

= 0.09906 moles of N

Now you can apply avagados number to this. (1 mole of any element has 6.022x10^23 atoms. 1 mole of any molecule has 6.022x10^23 molecules)

Number of atoms = 0.09906 x 6.022x10^23

= 5.965 x 10^22 atoms

EDIT: sorry, just realised I made a mistake in formula weigth and have fixed it

Answer 2

Start by computing the molecular weight of magnesium nitride: 72+28 = 100.  So 5 grams is 0.05 moles; and with 2 atoms of N per molecule, there are 0.10 moles of nitrogen.  Multiply by Avogadro to get 6E22 atoms of nitrogen.

Answer 3

Start by converting grams to moles.  To do this, you have to know the gram formula weight of Mg3N2.  Wikipedia says it's 100.95 g.

5g ÷ 100.95g/mole = 0.0495 moles.  

Avogadro's number is 6.022 x 10^23 atoms per mole

0.0495 moles x 6.022 x 10^23 atoms/mole = 0.298 x 10^23 atoms

But there are 2 nitorgen atoms in the compound, so double the last result:

0.298 x 10^23 x 2 = 0.596 x 10^23 = 5.96 x 10^22 atoms of N.

Btw, the other answer above miscalculated the formula weight.

Answer 4

Determine the molar mass:

Mg: 3*24.305=72.915 g/mol

N: 2*14.01=28.02 g/mol

Total:       100.94 g/mol

Convert the 5 g into moles

5g/(100.94g/mol)=.0495 mol

Then, take the # of moles times Avogadro's number (6.023*10^23) to get the #s of molecules

.0495mol*(6.023 mol^-1)=2.98*10^22

You now have the number of molecules, so in order to find the number of Nitrogen atoms, simply multiply that number by how many atoms of Nitrogen per molecule (in this case 2)

(2.98*10^22)*2=5.967*10^22 atoms of N

Answer 5

you need to divide 5 grams by the formula weight of Mg3N2 and then multiply it by avogadros number - 6.022 x 10 ^23.

5 x 6.022 x10^23 / 100.929 = 2.98 x 10^22

Answer 6

You aren't doing them right.

You first divide the 5 grams by the mole wt of Mg3N2.  This gives you the MOLES of the compound

Now multiply your result by Avagodro's #

Now double it, since each molecule of the compound contains 2 atoms of N.