Help me with his question!! confusing but not hard (1 Viewer)

[kooltrainer]

3) A household cleaning agent contains a weak base of general forumla Na2 X.
1.59g of this compound was dissolved in 100 ml of water. A 20ml sample of the solution was titrated with 0.25 mol/L HCl and required 24ml of the acid for neutralisation.

a) write neutralisation equation between Na2X and HCl
b) Calculate molar mass of the base and identify it..



cheers

 

[kooltrainer]

hello?

 

[wixxy2348]

well are you sure there's meant to be a 2 in there?
sounds awfully like NaOH to me..
coz then
a) NaX + HCl -> NaCl + HX (HX representing water coz water + a salt are products of neutralisation reaction)

 

[wixxy2348]

and i'm stuck on part B
apart from the identifying the base
umm if i were doing that question in an exam i'd work backwards
calculate molar mass of NaOH
and then have that & what it is written down etc etc

(I NEED TO REVISE TITRATION CALCULATIONS!!!)

 

[kooltrainer]

it says Na2X though...

 

[minijumbuk]

a) Na₂X + 2HCl --> 2NaCl + H₂X (Charge of X is 2-, as deduced from the substance Na₂X. Since molar ratio of Na:X is 2:1, and charge of Na is 1+, then X must be 2-)

b) Moles of HCl required in titration = 0.25 mol/L x 0.024 L
= 0.006 mol
Therefore 0.003 mol of Na₂X required (molar ratio 2:1)
Only 20/100 mL of the 1.59 g was used, so:
1.59 x 20/100 g of Na₂X contained 0.003 mol
0.318 g contained 0.003 mol Na₂X

So mass/molar mass = moles,
0.318 / (2x23 + X) = 0.003
X=60

Therefore molar mass of base is 2x23 + 60 = 106

Since it tells you in the beginning that it is a weak household cleaning product, you should have known it was Na₂CO₃. So now, test the molar mass of CO₃. If it is 60, then you will have proved the base's identity.

 

[kooltrainer]

oic

 

[minijumbuk]

well are you sure there's meant to be a 2 in there?
sounds awfully like NaOH to me..

Well, if it really was a typo of Na2 instead of Na, you should still know that NaOH is not a weak household cleaning base.

 

[wixxy2348]

Well, if it really was a typo of Na2 instead of Na, you should still know that NaOH is not a weak household cleaning base.

haha that thought did occur to me, after posting and after logging off (by which point i wasn't bothered returning loL). NaOH is litke drain cleaner isnt it? LOL.