Question

How many grams of ethane gas (C2H6) are in a 12.7 liter sample at 1.6 atmospheres and 24°C? Show all work used to solve this problem.

Answer 1

Any ideas on how to do this one?

Answer 2

Use the formula and plug in the atmosphere and temp

Answer 3

and volume

Answer 4

To find what?

Answer 5

N of C2H6 and use the formula again

Answer 6

Close! When you get n of C2H6, what formula will you use to get g of C2H6?

Answer 7

i dont know

Answer 8

From moles of C2H6, you can use the molar mass to get to mass of C2H6.

Answer 9

would that be what we did last time of multiplying?

Answer 10

Yup, something like that.

Answer 11

oh ok

Answer 12

n=1.03

Answer 13

Hm, I get it a little different.

Answer 14

What did you get?

Answer 15

0.83 mol

Answer 16

ok so i did 1.6*12.7=n*.0821*24 == 20.32=n*19.704

Answer 17

You have to change your temp to K.

Answer 18

ohh thats why

Answer 19

297.15k?

Answer 20

Yup, remember the units of R. They all have to match the units you are using in the rest of the equation.

Answer 21

ok got it n=.833

Answer 22

.833 mol C2H6

Answer 23

Yay!

Answer 24

now do we just plug it in again?

Answer 25

Plug it into what?

Answer 26

PV=nRT

Answer 27

no right

Answer 28

We have moles of C2H6, so we just need to use molar mass to get mass of C2H6.

Answer 29

what is the formula for that again?

Answer 30

12.01*2+1*6=30.02g/mol

Answer 31

where did you get all those numbers from

Answer 32

atomic mass of each element*number of that element all summed up

Answer 33

ohh ok

Answer 34

so would 30.02 be the Volume

Answer 35

NVM thats our new N

Answer 36

No, it's the molar mass of C2H6.

Answer 37

ok and now we get the mass with that

Answer 38

You got it :)

Answer 39

wait

Answer 40

whats the difference between the molar mass and mass

Answer 41

molar mass is the mass per mole

Answer 42

and mass would be the whole thing?

Answer 43

Mass is the mass given in the problem.

Answer 44

which is 12.7L right

Answer 45

Im lost

Answer 46

L is a unit of volume

Answer 47

yeh so what would be the mass that was given in the problem

Answer 48

In this case, mass is what we are looking for.

Answer 49

ok how do we find it using molar mass

Answer 50

But it is dependent on the problem. The molar mass is the same for each compound, no matter the problem.

Answer 51

0.833 moles C2H6 *(30.02 g C2H6/1 mol C2H6) = ? g C2H6

Answer 52

Thats what had me confused because in the last problems we would use two different compounds i did not know you could use the same for the formula

Answer 53

Hm, I'm not sure what you mean.

Answer 54

For example .885 mol Ca*(1 mol O2/2 mol Ca) we used O2 and Ca

Answer 55

That is a molar ratio based on the balanced reaction.

Answer 56

What we are using now is the molar mass.

Answer 57

ohhh ok

Answer 58

so what would be the answer to 0.833 moles C2H6 *(30.02 g C2H6/1 mol C2H6) = ? g C2H6

Answer 59

Multiply by the numerator and divide by the denominator.

Answer 60

Yeh i know that part but it dosent matter if we have different unit like Mol and Grams

Answer 61

You can use a ratio as long as the ratio is an equality.

Answer 62

30.02g C2H6 = 1 mol C2H6

Answer 63

so would the answer be 36.038

Answer 64

I get 25 g

Answer 65

.833*30.02

Answer 66

ahh got it

Answer 67

ok so 25.006

Answer 68

:)

Answer 69

and now we have our n

Answer 70

That is mass.

Answer 71

25 g

Answer 72

now we transfer the mass to moles

Answer 73

We wanted mass, so we are done! :)

Answer 74

ohh right

Answer 75

so the answer is 25g

Answer 76

but if we wanted to convert it to mole we would do 25/30?

Answer 77

ok i got it

Answer 78

thats the part that always gets me

Answer 79

You got it!

Answer 80

Just look at the units.