Science people! Anyone please put me out of my misery with a GCSE Chemistry question?

[Stumpedasatree]

I'm ashamed to say it is completely flummoxing me - and I have a biochemistry degree.

I understand to get the average of the three citric acid titration volumes (Titration 2, Titration 4, Titration 5) to give 12.13 cm3. But that's as far as I can go. I do have the answer but do not know how to work it out. Any help would be very gratefully received!

1 mol citric acid : 3 mol NaOH.
work out moles of NaOH. Divide by 3.
use volume of titration to work out conc.

I think. It's been a long time...

Oh I used to love chemistry. Got 99% in an exam once and an A at A level. Whilst the words are familiar and the symbols I now, 43 years later have not a clue

Thank you! But where does the given concentration of NaOH come in (0.102 mol /dm3)?

Mr DrSeuss interloper here.
We have that the average of the good titrations is 12.13333. From the equation given, we know that the number of moles of citric acid is 1/3 of the moles of sodium hydroxide so

Moles of sodium hydroxide= volume X concentration

Say volume was V so moles NaOH = V * 0.102
Moles citric = (V * 0.102)/3

Concentration= moles/ volume
Concentration citric = (V ml 1.02 mol/dm3)/(3 12.3333 ml)

Write the units (ml, mol/dm3) for full marks. The ml cancel and the answer comes out in mol/ dm3, as it should.

The problem is we don't know V. It should be given further up the page. Something like "25 ml portions of sodium hydroxide were titrated and .......". Without that the question is not answerable.

As DrSeuss suggests, for a GCSE titration question, you will have been given the volume of sodium hydroxide somewhere in the question stem. Once you've found it (and converted from cm3 to dm3 if necessary), then it should be straightforward.

Yes! Volume of NaOH is 25cm3. It was on the previous question and I hadn't realised. Now trying to do the calculation

I've done it - citric acid concentration answer is 0.07 mol/dm3. Thank you so much

If they are being very picky the answer should be given to the precision of the input data, which is 2 figures. So it's 0.0689, rounding to 0.069

Thank you @DrSeuss !! I know who to ask next time 😀 My DD was driving me mad - I was sure there was a bit of info missing but every time I tried to turn the page to the previous one which had part a) of the same question (and the NaOh titration volume) she batted my hand away saying I didn’t need to see it to answer the question 🤦‍♀️

Glad to help although it's actually Mr Seuss, a chemist, commenting. I have a degree in French and English!

Wish I understood all that. I salute you scientists.