chemistry question

Lithium reacts with water to produce hydrogen.
Li(s) + H2O(l) → LiOH(aq) + ½H2(g)
(a) In an experiment, 0.069 g (0.01 mol) of lithium produced 90 cm3 of hydrogen atroom temperature and pressure. What is the percentage yield of hydrogen?
[1 mol of any gas occupies 24 dm3 at room temperature and pressure.](
a)45% b)60% c)75% d)90%

can someone explain this

Reply 1

Chopinnocturne31

21

Use the moles of lithium to work out the number of moles of hydrogen there should be (using the equation). Then work out the fact that 90cm3 of hydrogen gas is produced to work out how many moles of hydrogen were really produced. Then you can use those two values to work out the percentage yield. Let me know if you need anymore help :smile:

Reply 2

LenaB5764

OP

11

I did the moles so I got 0.01 mil for Li therefore the moles for hydrogen is half of that so 0.005. Then I don’t know what to do

Reply 3

Chopinnocturne31

21

Original post by LenaB5764

I did the moles so I got 0.01 mil for Li therefore the moles for hydrogen is half of that so 0.005. Then I don’t know what to do

Ok, that's a good start! Now you can use the RTP formula n=V/24 to find the moles of hydrogen that were actually produced in the experiment. Don't forget to convert cm3 to dm3 :smile:

and then put your values into the formula for percentage yield: actual yield/theoretical yield x 100

Do you want me to explain why you need to do all of this because it might help for future questions as well, rather than just memorising what to do?

Reply 4

LenaB5764

OP

11

Original post by Chopinnocturne31

Ok, that's a good start! Now you can use the RTP formula n=V/24 to find the moles of hydrogen that were actually produced in the experiment. Don't forget to convert cm3 to dm3 :smile:

and then put your values into the formula for percentage yield: actual yield/theoretical yield x 100

Do you want me to explain why you need to do all of this because it might help for future questions as well, rather than just memorising what to do?

ok so if i do 90/1000 divide by 24 i get 3.75*10^-3 which is the mole of hydrogen but i am slightly confused as to whether this is the actual or the theoretical.

Reply 5

Chopinnocturne31

21

Original post by LenaB5764

ok so if i do 90/1000 divide by 24 i get 3.75*10^-3 which is the mole of hydrogen but i am slightly confused as to whether this is the actual or the theoretical.

Yes, that’s correct! That would be the actual yield because it is what happened when the person ACTUALLY did the experiment. The theoretical yield is what you would expect to be produced from the number of moles of lithium theoretically, but because of other experimental factors, in real life, the full thing wouldn’t be produced. My explanation is a little bit wordy lol so if you need any clarification, just let me know :smile:

Reply 6

LenaB5764

OP

11

Original post by Chopinnocturne31

Yes, that’s correct! That would be the actual yield because it is what happened when the person ACTUALLY did the experiment. The theoretical yield is what you would expect to be produced from the number of moles of lithium theoretically, but because of other experimental factors, in real life, the full thing wouldn’t be produced. My explanation is a little bit wordy lol so if you need any clarification, just let me know :smile:

Ok so if that’s the actual yield what is the theoretical yield?

Reply 7

Emily5243

14

Original post by LenaB5764

Ok so if that’s the actual yield what is the theoretical yield?

The expected moles of hydrogen based on how many moles of lithium there are.

Spoiler

Reply 8

LenaB5764

OP

11

Original post by Emily5243

The expected moles of hydrogen based on how many moles of lithium there are.

Spoiler

Thank you so much

Reply 9

LenaB5764

OP

11

Original post by Chopinnocturne31

Yes, that’s correct! That would be the actual yield because it is what happened when the person ACTUALLY did the experiment. The theoretical yield is what you would expect to be produced from the number of moles of lithium theoretically, but because of other experimental factors, in real life, the full thing wouldn’t be produced. My explanation is a little bit wordy lol so if you need any clarification, just let me know :smile:

Thank you so much for your help.