How many moles are there in 397 grams of #Na_2SO_4#?

2 Answers
Apr 8, 2017

Answer:

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"#

Apr 8, 2017

Answer:

#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#