Given 1.82*10^4mg of diphosphorous pentoxide.... how many molecules are there?

Question

Given 1.82*10^4mg of diphosphorous pentoxide.... how many molecules are there?

Answer 1

30.97 g P/mol P

16.0 g O / mol O

diphosphorus pentoxide = P2O5

2 * 30.97 + 5 * 16.0 = grams of P2O5 / mol of P2O5

141.94 g P2O5 / mol P2O5

1 mol = 6.022E23 "things"  (in this case molecules of P2O5)

1.82E4 mg P2O5 * (1 g P2O5 / 1000 mg P2O5) * (1 mol P2O5 / 141.94 g P2O5) * (6.022E23 molecules P2O5 / 1 mol P2O5)

7.7216E22 molecules of P2O5

Answer 2

1.82 x 10^4 mg = 18.2 g

Moles P2O5 = mass / molar mass =

=18.2 g / 142 g/mol = 0.128

Molecules = moles x Avogadro's number =

=0.128 x 6.02 x 10^23 = 7.72 x 10^22

Answer 3

I know other people already answered but I thought you might be curious on how to do it yourself so I explained my steps:

To find how many molecules you must do a simple conversion from mg to g to moles of molecules to just molecules:

referencing the periodic table of elements:

Oxygen is ~16 g/mol

Phosphorous is ~31 g/mol (you can get more exact numbers if that is your preference)

you have 5 oxygens and 2 phosphorous in the molecule

so 5 * 16 = 80

and 2 * 31 = 62

the molecular weight of your compound is ~142 g/mol

there is 1 g for every 1000mg

18200mg *(1g/1000mg) = 18.2 g

you are trying to get moles right now so flip your molecular weight and multiply:

18.2g * (1mol/142g) ~ .128 mol of molecules



a mol is just a number, it is 6.02*10^23

.128 mol * (6.02*10^23) = 7.71 * 10^22 molecules

side note: I'm lazy and I didn't use " significant figures" or whatever but hopefully this helped you so you can do it on your own!