Quick Revision - pH titration curve calculations

[@osarogbe394]

You are so helpful. I literally watched this 5 minutes before my OCR paper today, and it came up. Thanks so much!

[@sv8972]

Hi, do you happen to have a quick revision video on structure of graphite, diamond etc. Like their MP.

[@t.o8386]

hi sir, for Q1)E), how do you know that doubling the concentration will half the equivalence point? thank you!!

[@MaChemGuy]

Just think about any acid-alkali titration. If you doubled the concentration of the acid in the burette, the titre would half

[@t.o8386]

@@MaChemGuy thanks! :)

[@shaaysd558]

why didn't you subtract the moles of KOH with CH3COOH if the KOH is in excess?

[@nisargapoudel3911]

for the second question, how do u know where to draw the equivalence point exactly at like which pH u start?

[@Ika-zg7vz]

It doesn't matter, just make sure that it is above pH 7 (as it's a weak acid/strong base combo, SA/WB's equivalence point is below pH 7)

[@chris5207]

for q2 - it doesnt mention the temp being 25c so can we assume kw is 1x 10-14 if the question doesnt mention the conditions

[@MaChemGuy]

You’d have to yes. I took this directly from a paper so that’s how it appeared

[@oyindamolaadekoya9413]

In the a level exams, would you recommend doing the multiple choice questions first or last? And how much time time should I spend on the them?

[@MaChemGuy]

I recommend my students to do them last. Leave around 25-30 mins.

[@oyindamolaadekoya9413]

Ok, thank you!

[@FR-tn4qj]

Hi, thank you very much as you predicted this came up. But I am really stressing right now since I have done the curve starting from ACID ph then finished at alkali pH as required but I never drew a curve it was more like 3 straight lines. So I went with a ruler till equivalence point then drew another straight line till final pH. Will I get penalised?

[@lumiinouss4744]

unfortunately it will because its not supposed to be straight lines, but if you got the correct alkali Ph and correct H+ Ph you should get 2/3 marks

[@FR-tn4qj]

@@lumiinouss4744 I feel so guilty 😢 I am such an idiot literally never thought about the curve even though it clearly says 'curve'? Also do you remember if the first question said state the block and explain why? I literally just said 'block s' and never gave an explanation for it.

[@lumiinouss4744]

@@FR-tn4qj wait it didnt say explain? i dont remeber seeing explain ..

[@lumiinouss4744]

@@FR-tn4qj i also made a silly mistake converting 0.037g into mg :( instead of multiplying by 1000 i divided by 1000 like an idiot (oh and your right someon just told me)

[@FR-tn4qj]

@@lumiinouss4744 this is bad literally one mark down the drain I never read 'explain'

[@timothypopoola8403]

Im not sure but i think you have made a mistake in the calculation of moles of OH-. Seems to be out by a factor of 10 which would make the answer 12.63 instead of 11.63

[@hk4560]

nar mate

[@timothypopoola8403]

@@hk4560 don’t matter for me anymore mate

[@livyaxx8203]

hi there, just wondering if the AS 2019 exam papers are available to you?

[@MaChemGuy]

Livya Xx Sorry but I’m not allowed to share. Can’t you badger your teacher??

[@livyaxx8203]

​@@MaChemGuy Yes I will drop her an email again if it is already out as I emailed her on Thursday and she told me it was not available yet.

[@MaChemGuy]

Livya Xx If your school/college doesn’t do AS it’s not available till August.

[@livyaxx8203]

@@MaChemGuy oh right! That sucks. Thanks for letting me know sir

[@yulka831]

Which exam board do you teach?

[@user-gi3yr1gl7j]

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