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# TITRATIONS HELP (AS level) watch

1. Hello,

I'm doing OCR A LEVEL chemistry and I'm really struggling with the titration topic, do you guys reccommend any good resources which could help me out?

Also, i'm a bit stuck on this question, I feel like I'm doing it wrong
3. (Original post by noor.m)
Hello,

I'm doing OCR A LEVEL chemistry and I'm really struggling with the titration topic, do you guys reccommend any good resources which could help me out?

Also, i'm a bit stuck on this question, I feel like I'm doing it wrong
a) No. of moles of KOH used in the titration: n = c x v, therefore 1.05 x 0.025 = 0.02625 moles (divide the volume in cm^3 by 1000 to convert to dm^3)

b)Concentration of diluted acid: so the equation shows that the mole ratio for KOH : H2SO4 is 2:1, therefore half the number of moles of H2SO4 react with KOH, so 0.02625/2=0.013125 moles of H2SO4
Concentration is c=n/v so 0.013125/0.02080=0.631 mol/dm^3
4. (Original post by aa98)
a) no. Of moles of koh used in the titration: n = c x v, therefore 1.05 x 0.025 = 0.02625 moles (divide the volume in cm^3 by 1000 to convert to dm^3)

b)concentration of diluted acid: So the equation shows that the mole ratio for koh : H2so4 is 2:1, therefore half the number of moles of h2so4 react with koh, so 0.02625/2=0.013125 moles of h2so4
concentration is c=n/v so 0.013125/0.02080=0.631 mol/dm^3
5. (Original post by noor.m)
Hello,

I'm doing OCR A LEVEL chemistry and I'm really struggling with the titration topic, do you guys reccommend any good resources which could help me out?

Also, i'm a bit stuck on this question, I feel like I'm doing it wrong
Hi may i suggest that you draw so that it is clear what is happening. it was how i was taught and it is how i teach. easier with everything laid out clearly. when is mole changing? when is conc changing?
6. (Original post by shengoc)
Hi may i suggest that you draw so that it is clear what is happening. it was how i was taught and it is how i teach. easier with everything laid out clearly. when is mole changing? when is conc changing?
We were taught that today in lesson but I didn't really understand him, could you go through it in a bit more detail if you can?
7. this is the idea of dilution, chemguide or Jim Clark's book can provide good details. Important is two or more diagrams.

You start with concentrated stuff, when you add water to DILUTE, its concentration changes (decreases) but since you are just adding water, how can mole of "substance" change?

The solution in your volumetric flask is your stock solution, an important part of planning assessment in A-level involves how to make stock solution from concentrated solution or from a solid.

Anyhow, the next step is what do you do with your stock solution? does it go into the burette or pipette?

Where you pipette out 25.0 cm3 from a 250 cm3 volumetric flask, that is a nice factor of 10 in terms of how the mole decreases, but the concentration is the same, since they come from the same flask.
usually, mole reacted in titration = x
then total mole in 250 cm3 = 250/25 * x

In this question, if you read, the diluted solution goes into the burette. hence,
if average best titres are y cm3 for example, then
mole of NaOH = (1)
mole of H2SO4 in y cm 3 = 1/2 * (1) depends on mole ratio
use direct proportion to find out mole of H2SO4 in the total 500 cm3 (simply because the qst specified 500 cm3 stock solution rather than 250 cm3).

The rest should be working backward - my former chemistry tutor called this "back titration" problems. Good luck.

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