Titrations help

Hi,

I'm working through some practice exam questions at the moment and there is one that I am really struggling with. Could anyone possibly help me with the method of how to work it out? I don't want to be given the answer as I still want to attempt it!

Question: 8.58g of coastic soada was dissolved to produce a solution of 500cm3 .to neutralize 50cm3 of this solution 15cm3 of 0.4M HCl was consumed .(coastic soada = Na2CO3.XH2O ) find the value of X?

Thanks!

(edited 7 years ago)

Reply 1

Pigster

20

What have you tried so far?

Reply 2

loisss_x

OP

Original post by Pigster

What have you tried so far?

So far all I've been able to do is work out the number of moles there is in the Sulphuric Acid.

I understand that the simplest way to start is by coming up with a balanced equation, which I'm fine with doing in the types of Titration questions I'm used to, but I've not really done any work with water of hydration and I'm at a loss for how to write an equation using the .xH20 part.

Thanks for the reply.

Reply 3

coconut64

16

Original post by Pigster

What have you tried so far?

Sorry to jump in but is x =10? Cheers

Reply 4

loisss_x

OP

Original post by coconut64

Sorry to jump in but is x =10? Cheers

Jump in all you want, I'm clueless!
How did you come up with 10 as the answer?

Reply 5

coconut64

16

Original post by loisss_x

Jump in all you want, I'm clueless!
How did you come up with 10 as the answer?

Is that right though ? I don't wanna be misleading

Reply 6

Pigster

20

I haven't done the calculation, but Na2CO3 is usually .10H2O

Reply 7

Pigster

20

Original post by loisss_x

I'm at a loss for how to write an equation using the .xH20 part..

When you drop Na2CO3.xH2O(s) into water, you'll end up with Na2CO3(aq)

i.e. when you react it with sulfuric acid, you don't have to worry about the waters of crystalisation in your balancing.

Reply 8

Federerr

19

Find the moles of H2SO4:

Moles = Concentration x Volume

20cm^3 you want it in dm^3 so you divide is by 1000.

0.05 x 0.02 = 0.001 moles

If you have a balanced equation for this reaction you know the molar ratio is 1:1

So moles for Na2CO3 will be 0.001 as well.

Now just find out the mass of Na2CO3 disregarding the xH20

Mass = Mr x Moles

106 x 0.001 = 0.106g

Now you know Na2CO3 is 0.106g take it away from the total mass:

0.286-0.106 = 0.18

Now just find the moles of water:

Moles = Mass/Mr

0.18/18 = 0.01

So now the molar ration between Na2CO3 and H20 is:

0.001 : 0.01

So divide both sides by the smallest number which is 0.001 to give you the following ration

1:10

Hence x being 10.

(edited 7 years ago)

Reply 9

Pigster

20

Original post by Federerr

now remember to x1000 as you converted the volume of sulfuric acid from Cm^3 to Dm^3

0.01 x 1000 = 10

So x = 10

I'm not sure about the last bit.

I would suggest the following logic:

0.001 mol of Na2CO3 has 0.01 mol of H2O (as water of crystalisation)

i.e. 0.001 : 0.01

diving both numbers by the smallest number gives:

0.001/0.001 : 0.01/0.001 =

1 : 10

i.e. 1 mol of Na2CO3 has 10 mol of water

i.e. Na2CO3 . 10H2O

Reply 10

Federerr

19

Original post by Pigster

I'm not sure about the last bit.

I would suggest the following logic:

0.001 mol of Na2CO3 has 0.01 mol of H2O (as water of crystalisation)

i.e. 0.001 : 0.01

diving both numbers by the smallest number gives:

0.001/0.001 : 0.01/0.001 =

1 : 10

i.e. 1 mol of Na2CO3 has 10 mol of water

i.e. Na2CO3 . 10H2O

Yes now I remember! I almost forgot how to do this, so I pretty much made up a nonsense way to make up 10 as x haha.

Yep now I remember that you need to divide by the smallest to get 1:10.

I'll edit my post now. Thanks :smile:

Reply 11

coconut64

16

Original post by Federerr

Yes now I remember! I almost forgot how to do this, so I pretty much made up a nonsense way to make up 10 as x haha.

Yep now I remember that you need to divide by the smallest to get 1:10.

I'll edit my post now. Thanks :smile:

Just a random person passing by but smoking is bad for you and u shouldn't really glorify it. Not cool