Answer:
O
2 has a mass of 1.78g
Explanation:
We are at STP and that means we have to use the ideal gas law equation!
P represents pressure (could have units of atm, depending on the units of the universal gas constant)
V represents volume (must have units of liters)
n represents the number of moles
R is the universal gas constant (has units of
L
×
a
t
m
m
o
l
×
K
)
T represents the temperature, which must be in Kelvins.
Next, list your known and unknown variables. Our only unknown is the number of moles of
O
2
(
g
)
. Our known variables are P,V,R, and T.
At STP, the temperature is 273K and the pressure is 1 atm. The proportionality constant, R, is equal to 0.0821
L
×
a
t
m
m
o
l
×
K
Now we have to rearrange the equation to solve for n
n
=
P
V
R
T
n
=
1
atm
×
1.25
L
0.0821
Lxxatm
m
o
l
×
K
×
273
K
n
=
0.05577
m
o
l
To get the mass of
O
2
, we just have to use the molar mass of oxygen as a conversion factor:
0.0577
mol
O
2
×
32.00
g
1
mol
= 1.78g
O
2
