Year 12s: what will be the first way you research your future options? >>

Sodium reaction question

How would I work this out?

2Na + 2H₂0 > 2Na⁺+ 2OH^-+ H₂How many moles of sodium are needed to release 1l of hydrogen and standard temperature and pressure? From what I have been told 24 litres of gas is equivalent to 1 mole at room temperature and sea level.

Reply 1

yangg

Find how many moles of hydrogen there is, and then use the ratios given in the equation to work out correspondingly how many moles of sodium is needed.

Reply 2

james188

So the ratio is 2:4 or 1:2?

Reply 3

Borek

Original post by james188

So the ratio is 2:4 or 1:2?

You are either right or wrong, hard to tell.

Ratio of what to what?

Reply 4

james188

2 sodium to every 4 hydrogen. What I don't understand is how to calculate how much gas is given off.

Reply 5

Borek

Original post by james188

2 sodium to every 4 hydrogen.

That's not correct. While I see 2 sodium atoms (moles) on the LHS, I see just a single hydrogen molecule on the RHS.

What I don't understand is how to calculate how much gas is given off.

You don't have to calculate how much gas is given off - it is given to you, You just have to convert 1 L to moles. Yes, you can assume for that than 1 mole is 24 L at STP.

(edited 10 years ago)

Reply 6

james188

Ok thanks. So to find the answer I would have to divide the one hydrogen by 24 to get my 1 litre and then divide the starting sodium by 24 as well?

Reply 7

amongsttheweeds

Original post by james188

Ok thanks. So to find the answer I would have to divide the one hydrogen by 24 to get my 1 litre

You were on the right track here. Now think about how many moles of sodium you need to react, to produce the number of moles of hydrogen you just calculated. Look at the equation you are given.

Posted from TSR Mobile

Reply 8

james188

So I should be dividing my 2 moles of sodium (2x23) by 24 as well?

Reply 9

amongsttheweeds

Original post by james188

So I should be dividing my 2 moles of sodium (2x23) by 24 as well?

2/24 will get you the right answer but I don't know if you're following the right thought process.

1 mole of H2 = 24 L of H2
So 1 L of H2 = 1/24 moles

Then look at the mole ratios. You need twice as many moles of sodium as you need of hydrogen.

2 x 1/24 = 2/24 and I don't have a calculator to work it out. :smile:

Posted from TSR Mobile

(edited 10 years ago)

Reply 10

amongsttheweeds

Original post by addylad

2/24 will get you the answer but I don't know if you're following the right thought process.

1 mole of H2 = 24 L of H2
So 1 L of H2 = 1/24 moles

Then look at the mole ratios. You need twice as many moles of sodium as you need of hydrogen.

So 2 x 1/24 = 2/24 and I don't have a calculator to work it out. :smile:

Posted from TSR Mobile