Another HSC question help (1 Viewer)

[abdog]

A student used the titration process to determine the concentration of a potassium hydroxide solution. She found that 25ml of a 0.1mol/L sulphuric acid solution reacted with exactly 10ml of the potassium hydroxide solution. Calculate the concentration of the potassium hydroxide solution.

I used this formula: C1V1=C2V2.

But for some reason the answer uses this: C1V1=2 x C2V2

Can anyone explain why?

 

[Alkanes]

Write out the chemical equation and then balance it. Should tell you why.

 

[abdog]

The chemical equation is:

2KOH + H2SO4 ---> K2SO4 + 2H20.

I still don't get it...

 

[Alkanes]

For 1 mole of sulfuric acid there are 2 moles of potassium hydroxide.

 

[abdog]

Yes, but how does that affect the formula?

EDIT: OK I get it now! Thanks!

 

[madharris]

C1V1 = C2V2 is only when the ratios are 1:1

If it's not then you can use
(CaVa)/a = (CbVb)/b

where Ca,Cb = concentrations of acid and bases
Va, Vb = volumes of solutions
a, b = molar co-efficients from the balanced equation