Think, Discuss and Write
1. Look at the examples below and in each of them, discuss which is better comparison.
In the atmosphere, I g of air contains:
.78 g Nitrogen, .21 g Oxygen .01 g Other gas
or
78% Nitrogen, 21% Oxygen, 1% Other gas
2. A shirt has:
3/5 Cotton, 2/5 Polyster
or
60% Cotton
or
40% Polyster
Answers
Answer:
78 percentage Nitrogen
21 percentage oxygen
1 percentage other gases
Step-by-step explanation:
0.78 atm
Explanation :
As you know, the partial pressure exerted by a gas that's part of a gaseous mixture depends on two things
the total pressure of the mixture
the mole fraction of that gas
Your equation will look like this
P
gas
=χ
gas
×P
total
P
gas
- the partial pressure of a gas
χ
gas
- the mole fraction of that gas
P
total
- the total pressure of the mixture
In this case, you know that the total pressure of the mixture is equal to 1.0 atm. Now, in order to find a gas' mole fraction, you need to know
the number of moles of that gas present in the mixture
the total number of moles present in the mixture
You don't know exactly how many moles of the mixture you have, but you do know one important thing.
More specifically, you know that 78.0% of all the molecules present in the mixture are nitrogen molecules, 21.0% are oxygen molecules, and 1% are molecules of other gases.
As you know, a mole is simply a very large collection of molecules. In order to have one mole of a substance, you need to have 6.022⋅10
23
molecules of that substance.
This means that the actual number of moles is not important here, because the ratio that exists between the number of molecules is equivalent to the ratio that exists between the number of moles.
So, if you have 100 moles of air, you know that 78 will be moles of nitrogen, 21 will be moles of oxygen, and 1 mole will be other gases.
So, let's say that you have x moles of gas. You can say that the mole fraction of nitrogen will be
χ
N
2
=
total number of moles
number of moles of N
2
The number of moles of nitrogen will be
x moles air⋅
100 moles air
78 moles ofN
2
=
100
78
x moles N
2
The partial pressure of nitrogen will thus be
P
N
2
=
100
78
⋅1.0 atm=0.78 atm.
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