How many moles are there in 397 grams of Na_2SO_4?

2 Answers
SCooke
Apr 8, 2017

2.80

Explanation:

A mole is a unit-molecular weight (grams/mole in this case) of an Avogadro's number of molecules or atoms. It is calculated for a molecule by adding up the individual atomic weights of its constituent atoms.

For Na_2SO_4 this is 2 x 23 = 46 for the sodium, plus 4 x 16 = 64 for the oxygen, plus 32 for the sulfur. That adds up to a molecular weight of 142 (g/"mole"). Now we divide the given number of grams by this value to derive the number of moles.
(397/142)(g/(g/"mol")) = 2.80 "moles"

David L.
Apr 8, 2017

n_(Na_2SO_4)=2.79 mol

Explanation:

Molar mass of Na_2SO_4 =142.04g/(mol)

Use the equation,

n_(Na_2SO_4)=m/M

where,

n= number of moles
m=mass (in grams)
M=molar mass (in (grams)/(mol))

n_(Na_2SO_4)=(397g)/(142.04(g/(mol)))

n_(Na_2SO_4)=2.79 mol

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