How many molecules are in 10.0 g of #O_2# gas at STP?

2 Answers
Feb 27, 2016

Answer:

How many molecules at STP? The same number of molecules in 10.0 g of LIQUID OXYGEN at LOW TEMPERATURES.

Explanation:

You specified a mass of 10.0 g. Clearly, this is a finite number of dioxygen molecules. This same finite number (which is #N_Axx(10.0*g)/(32.0*g*mol^-1)#, #N_A = "Avogadro's number"#) is the same mass whatever the state, solid, liquid, or gas.

Of course, at STP, dioxygen is a gas, but 10.0 g is still 10.0 g. We could calculate its volume at STP, which is #22.4# #L# #xx# its molar quantity, approx. #8*L#.

Feb 27, 2016

Answer:

There are #1.51xx10^23"molecules O"_2"# in #"10.0 g O"_2"#.

Explanation:

STP is irrelevant - it's a detractor. Mass is not dependent on temperature or pressure. The number of molecules of #"O"_2"# are dependent only on the moles of #"O"_2"# in #"10.0 g O"_2"#.

Determine the molar mass of #"O"_2"#, which is #(2xx15.998"g/mol")="39.998 g/mol"#.

#1"mol of molecules"=6.022xx10^23"molecules"#

You will make the following conversions:

#color(red)("mass O"_2)##rarr##color(green)("mol O"_2)##rarr##color(blue)("molecules O"_2)#**
by 1) dividing the given mass #"O"_2"# by its molar mass, and 2) multiplying mol #"O"_2"# by #6.022xx10^23"molecules".#

#color(red)10.0cancel(color(red)("g O"_2))xx(color(green)(1)cancelcolor(green)("mol O"_2))/(color(green)(39.998)cancelcolor(green)("g O"_2))xx(color(blue)(6.022xx10^23"molecules O"_2))/(cancelcolor(blue)("mol O"_2))=color(blue)(1.51xx10^23"molecules O"_2")# rounded to three significant figures