Question

The effusion rate of an unknown gas is measured and found to be 31.50 mL/min. Under identical experimental conditions, the effusion rate of O2 is found to be 30.50 mL/min. If the choices are CH4, CO, NO, CO2, and NO2, what is the identity of the unknown gas?

Answer 1

@iPwnBunnies @parna @primeralph

Answer 2

its kinetic molecular theory

Answer 3

@RatzLover95

Answer 4

Use Graham's Law of Effusion.

Answer 5

BUT HOW i never used this law

Answer 6

\[\frac{rate_a}{rate_b} = \sqrt{\frac{M_b}{M_a}}\]

Answer 7

im confused ?

Answer 8

The ratio of the two rates of two gases is equal to the square root of molar masses of the two gases, but flipped

Answer 9

i stil dont get it

Answer 10

We know the rate of effusion for the O2 and the unknown gas. We know the molar mass of O2 from the Periodic Table. We just need to find M of the unknown gas.

Answer 11

wait so 30.50 ml is ma?

Answer 12

No, that is the rate of one of the O2.

Answer 13

Let A be the O2, and B be the unknown gas. We're trying to find Mb.

Answer 14

ok and wats ma?

Answer 15

Ma is the molar mass of O2.

Answer 16

31.50ml/min is ma?

Answer 17

No..That's the rate of the unknown gas, B.

Answer 18

Let's solve for Mb first, that's what we're trying to find so we can identify the unknown gas.

Answer 19

is this right so far 30.50ml/min/31.50ml/min?

Answer 20

Yeah, that'll be the left side. Next step to isolate Mb?

Answer 21

how do you find ma though?

Answer 22

We can find Ma from the Periodic Table. O2 has two moles of oxygen in it. From the Periodic Table, we can see O has a molar mass of 16 g/mol.
So, O2 has a molar mass of 32 g/mol

Answer 23

oh ok so its 30.50ml/min/31.50ml/min=square root of mb/32g/mol?

Answer 24

Yes.

Answer 25

ok so the left anwser is .96ml/min?

Answer 26

Sure, I trust you can do that lol.

Answer 27

is it right?

Answer 28

Just that part? Idk...I'm pretty sure it should be that.
Now, next step in solving for Mb?

Answer 29

so for the square root dont you multiply by ^2 to cancel the square root symbol?

Answer 30

That's not multiplying. But you do square both sides to get rid of that square root.

Answer 31

oh i meant square sorry

Answer 32

so is the left 0.96ml/min^2?

Answer 33

Well, yeah. But you have to square the number for it to be useful. :3

Answer 34

so i square 32 as well?

Answer 35

Plus, there are no units, since when you divided those two rates, the units cancelled out.

Answer 36

@RatzLover95

Answer 37

No, when you square the right side, you just get rid of the square root there. The numbers don't change.

Answer 38

oh ok then wat?

Answer 39

then do u multpily 32 nd .96?

Answer 40

Well, what number did you get on the left side? You had to square 0.96.

Answer 41

yes?

Answer 42

o.o Square 0.96, since we squared both sides.

Answer 43

so u multpily square .96 and 32?

Answer 44

Err, ok, yeah, we can keep the square there for now.
Yes, now you'll have to multiply by 32 to get Mb by itself.

Answer 45

kay well i got 30.72?

Answer 46

You didn't square the 0.96 like I told you to.

Answer 47

(0.96)^2 * 32

Answer 48

so its 29.49?

Answer 49

but wats the unit for it tho?

Answer 50

It'll be g/mol. Remember, the rates cancelled out when you did the division. Then, when you multiplied by 32 g/mol, the g/mol went with it.
It also makes sense that we're solving the molar mass of Mb, it should be in g/mol.

Answer 51

so is 29.49 g/mol the final anwser?

Answer 52

But yes, 29.49 g/mol is the correct molar mass of the unknown gas. Use the Periodic Table and the list of gases given to figure out which one matches.

Answer 53

The question asks to identify which gas has that molar mass.

Answer 54

ok is it sodium?

Answer 55

It's not sodium, that's a metal. The question gives you about 6 different gases that can be the answer. You'll have to find the molar masses of all of them to find the right one.