PH of diprotic triproticetc

[lukew]

Hi came over a question ...:
Question 10
Citric acid, C6H8O7, the main acid in lemon juice, is a triprotic acid.
When 20.0 mL aliquots of lemon juice were fully titrated with 0.350 M NaOH, the volume of
the average titre was 37.09 mL.
What was the concentration, in g L-1, of citric acid in the lemon juice?
A. 0.831
B. 2.50
C. 41.5
D. 374

Solution : Since citric acid is triprotic then 1 mol C6H8O7 reacts with 3 mol NaOH
n(NaOH) reacting = 0.350 mol L-1 x 37.09x10-3 L
= 1.30x10-2 mol
n(C6H8O7) reacting = n(NaOH) / 3
= 1.30x10-2 / 3
= 4.33x10-3 mol
m(C6H8O7) in 20.0 ml = 4.33x10-3 mol x 192.0 g mol-1
= 0.831 g
c(C6H8O7) in g L-1 = (0.831 / 20.0) x 1000
= 41.5 g L-



*does this mean for  very acidic solutions such as nitric acid and h2so4 do we assume they get rid of their H all at once and mutliple their concentration or  divide to find mol by that number of h *?

[Graphite]

Weak acids completely ionise with strong bases.
Weak bases completely ionise with strong acids.

[cltf]

Look at it this way,
c(H2SO4) = 1M
c(H+) = 2M --> This is what the base is reacting with, so in a titration, 2 X n(NaOH) = n(H2SO4), 2 lots of base is required because the acid is donating 2 protons, so the mol of the acid is half the mol of the base. VCAA should state whether if it is mono, di or triprotic, so just divide by the number of H+ present if working backwards like the question.

[lukew]

OHHHHH I get it THANKS !!!

[VivaTequila]

Some questions have screwed me on these concepts.

How is it that the pH level occurs at 7 between weak acids and strong bases? Wouldn't it be higher?
Or is TSSM lying to me?

[david10d]

Some questions have screwed me on these concepts.

How is it that the pH level occurs at 7 between weak acids and strong bases? Wouldn't it be higher?
Or is TSSM lying to me?

Definitely higher, the pH level of 7 occurs when a strong acid and a strong base reacts

EDIT: LOLTYPO

[VivaTequila]

thank you, TSSM lies.

[burbs]

Some questions have screwed me on these concepts.

How is it that the pH level occurs at 7 between weak acids and strong bases? Wouldn't it be higher?
Or is TSSM lying to me?

Definitely higher, the pH level of 7 occurs when a strong acid and a weak ..base reacts

...pH of 7 for strong acid weak base whut? Pretty sure pH 7 is for strong acid strong base and if its strong acid weak base its pH <7.

[Greatness]

thank you, TSSM lies.

TSSM exams are hopeless.

[david10d]

Some questions have screwed me on these concepts.

How is it that the pH level occurs at 7 between weak acids and strong bases? Wouldn't it be higher?
Or is TSSM lying to me?

Definitely higher, the pH level of 7 occurs when a strong acid and a weak ..base reacts

...pH of 7 for strong acid weak base whut? Pretty sure pH 7 is for strong acid strong base and if its strong acid weak base its pH <7.

LOL SORRY, strong base strong acid.

[Water]

thank you, TSSM lies.

TSSM exams are hopeless.

TSSM exams are good papers.

[Greatness]

thank you, TSSM lies.

TSSM exams are hopeless.

TSSM exams are good papers.

I hate them. Their questions are ambiguous and their answers are terrible sometimes. Not gonna touch them for unit 4...

[maeve]

thank you, TSSM lies.

TSSM exams are hopeless.

TSSM exams are good papers.

They're mediocre at best - Better than TSFX, alas can't hold a candle to NEAP or Insight.

Getting majorly sick of cruddy papers. You get half way through it and decide its bloody pitiful and you've wasted an hour. -.- why do they bother distributing them?!

[jackson1234]

TSSM's exams will be good papers, when they understand that 2 lines of working will not be sufficient for a 4mark question.

[Andiio]

TSSM's exams will be good papers, when they understand that 2 lines of working will not be sufficient for a 4mark question.

C.Dwyer