Titration Question - confused with the last bit (1 Viewer)

[a1079atw]

Hi all,

Here's the question:


And here's the solution

What I don't get is for (c), where did the 0.0735mol came from.
Apparently it is half the concentration of H2SO4 from part (b), but why half it? And it's concentration, not mole anyway.
Please help, so confused.

 

[mysterymarkplz]

Because for every 1 mole of H2SO4, it reacts with 2 moles of NaOH,
H2SO4 + 2NaOH -> Na2SO4 + 2H2O
H2SO4 is diproctic, in the presence of a strong base (NaOH), it forces H2SO4 to fully ionize, neglecting the reversible part of HSO4 being amphiprotic, basically H2SO4 has 2 hydrogens and NaOH only has 1 OH.

 

[a1079atw]

Hand on, so is the mole remaining 0.0735mol because it is diprotic? or is it because only 500mL is used?
If it's because it is diprotic... I still don't get it since 0.147 is mol per Litre not mol, how can you just use it as mol?
Sorry I don't know if my questions makes sense...

 

[a1079atw]

Sorry please ignore the previous post I got confused
But one more question, sorry. For the concentration of acid in (b), why is the concentration 0.147 not 0.0735?
I thought [(2*Ca)Va]/1=[CbVb]/2, where 2*Ca=0.147 so shouldn't Ca=0.0735?

 

[mysterymarkplz]

Wait the answers are weird, could someone correct me but why does it say moles of n(NaOH) = 2n(H2SO4)? Thats like saying for every 1 mole of NaOH 2 moles of H2SO4 is neutralized, it should be the opposite? there are 2 hydrogens and 1 hydroxide...

 

[a1079atw]

I think it's because the answer is using this equation?

 

[HeroicPandas]

H2SO4 + 2NaOH -> Na2SO4 + 2H2O

You need 2 moles of sulfuric acid to neutralise 1 mole of sodium hyroxide

n(H2SO4) : n(NaOH) = 1 : 2

n(H2SO4)/n(NaOH) = 1/2

2 x n (sulfuric) = n (sodium hydro) (cross multiply)

 

[mysterymarkplz]

lol im an idiot, back to basics

 

[HeroicPandas]

lol im an idiot, back to basics

You are NOT an idiot

An idiot would accept the fact that blah = blah

 

[strawberrye]

lol im an idiot, back to basics

You are not an idiot, don't say that