How many grams of oxygen are in #6.15times10^23# formula units of #(NH_4)_2SO_4#?

1 Answer
Aug 1, 2017

Answer:

#65.4# #"g O"#

Explanation:

We're asked to find the mass, in #"g"#, of oxygen in #6.15xx10^23# #"formula units (NH"_4")"_2"SO"_4#.

To do this, we recognize that there are #4# #"atoms O"# per formula unit of ammonium sulfate:

#6.15xx10^23cancel("formula units (NH"_4")"_2"SO"_4)((4color(white)(l)"atoms O")/(1cancel("formula unit (NH"_4")"_2"SO"_4)))#

#= 2.46xx10^24# #"atoms O"#

Now, we use Avogadro's number to find the number of moles of #"O"#:

#2.46xx10^24cancel("atoms O")((1color(white)(l)"mol O")/(6.022xx10^23cancel("atoms O"))) = ul(4.085color(white)(l)"mol O"#

Finally, we use the molar mass of oxygen (#15.999# #"g/mol"#) to convert from moles to grams:

#4.085cancel("mol O")((15.999color(white)(l)"g O")/(1cancel("mol O"))) = color(red)(ul(65.4color(white)(l)"g O"#