Chemistry mole calculation problem (help me)

[xim7007]

50 cm3 of a solution of citric acid, Mr = 192, containing 19.2 g dm–3 reacted with 50 cm3 of a
solution of sodium hydroxide containing 12 g dm–3. Citric acid can be represented by the
formula HxA, where x represents the number of hydrogen atoms in the molecule. Use the
data above to calculate the number of moles of sodium hydroxide that react with one mole
of citric acid and hence find the value of x. Can anyone ans this question explaining how to find the value of X?

[Saladin]

50 cm3 of a solution of citric acid, Mr = 192, containing 19.2 g dm–3 reacted with 50 cm3 of a
solution of sodium hydroxide containing 12 g dm–3. Citric acid can be represented by the
formula HxA, where x represents the number of hydrogen atoms in the molecule. Use the
data above to calculate the number of moles of sodium hydroxide that react with one mole
of citric acid and hence find the value of x. Can anyone ans this question explaining how to find the value of X?

On it now, will post as soon as possible!

[Saladin]

First, you need to calculate the number of moles of Citric acid present.





Therefore one mole of Citric Acid reacts with one mole of NaOH. Now, you can see that the NaOH particle can make two ions, Na⁺ and OH^-.

So, therefore as there is a one to one ratio and NaOH can only produce one mole of hydroxide ions per mole of compound, this is an acid with a single Hydrogen atom in each molecule, as an acid and a base will make water.

H⁺+OH^-=H₂O

[xim7007]

I still don't understand.. what would be the value of X?... Concentrations are given in g/dm3

[Saladin]

I still don't understand.. what would be the value of X?... Concentrations are given in g/dm3

The value for X is 1, because there is 1 hydrogen in each molecule of Citric Acid.

[Saladin]

The answer they wanted here was not a concentration value, they wanted to know how many hydrogen atoms are in a molecule of Citric acid.

[nid404]

Citric acid conc= 19.2/192 mol/dm3 = 0.1 mol/dm3
conc=mol/dm3
No of moles=0.005 (50/1000dm3 X 0.1)

Mr of NaOH= 40
NaOH conc= 12/ 40 = 0.3 mol/dm3

Vol of NaOH that reacted= 50cm3
Moles of NaOH that reacted= 0.0015

In fact theres no need to find the moles. Ratio of conc gives the ratio of moles since volume is same.

Ratio of citric acid to NaOH is 1:3

H_xA+ 3NaOH --> Na₃A + 3H₂O

x=3

[nid404]

Hope this is clear.

[Saladin]

Citric acid conc= 19.2/192 mol/dm3 = 0.1 mol/dm3
conc=mol/dm3
No of moles=0.005 (50/1000dm3 X 0.1)

Mr of NaOH= 40
NaOH conc= 12/ 40 = 0.3 mol/dm3

Vol of NaOH that reacted= 50cm3
Moles of NaOH that reacted= 0.0015

In fact theres no need to find the moles. Ratio of conc gives the ratio of moles since volume is same.

Ratio of citric acid to NaOH is 1:3

H_xA+ 3NaOH --> Na₃A + 3H₂O

x=3

Ahh man, I messed up!

Sorry for the inconvenience. I just messed up for some reason. It was a really simple sum

[xim7007]

Thanks guys for ur kind help.

I was trying to do it this way. I found out the amount of citric acid and amount of NaOH in moles. I got 0.005 moles of citric acid reacts with 0.015 moles of NaOH, so 1 mole of citric acid reacts with 3 moles of NaOH. But I don't how to carry out further calculation to find the value of X. can u explain how to calculate the value of X using this method? 

[nid404]

Look at the equation carefully

Na has a charge of +1. The salt formed is Na₃A  which means A has charge of -3.

They say citric acid is H_xA

A has a charge of -3. H has a charge of +1. so x has to be 3 to balance the charge on the acid.

[xim7007]

Yup. I got it. Thanx a lot Ahana. 

[nid404]

Welcome (: