This is such a good video, I appreciate the way you explain your thought process of each step and detail the method and reasoning as that’s where I struggle the most with deciphering mark schemes.
amazing video. youre the best chemistry teacher i have encountered by FAR! quick question... the questions that you mentioned at 9:16, did you do an exam question walkthrough on this on you yt channel?
Thank you very much - I’m in the process of doing walkthroughs of all the MCQs in the exam papers (posted one today and there are some breadth in chem papers done already)
I met a girl at the UOM open day who recommended your channel to me, was not disappointed! she said she was one of your past students, can't remember her name though!
Hi, once you’ve started the calculation it won’t matter what brackets you use. Just make sure when writing the initial Ka (or Kc) expression you use square ones
Hi, the concentrations started in the question are not valid for the buffer as when you mix the two solutions together the total volume will change which would change each concentration (c = n/v). What you would need to do is re-calculate the adjusted concentrations to account for the change in the total volume now that the solutions are merged. Since this takes time and the volume terms would cancel out anyway, it is easier just to use moles.
@@mrmurraygreen Hey great video! Although, in the first question it says that “the student assumes that the volume of the solution does not change”. Does that mean we could have just plugged in the concentration values into that equation rather than using moles as the total volume hasn’t changed?
Hi, but the sodium salt isn’t a concentration? It’s a mass. It needs converting into moles to be used. Also sorry for the slow reply, the TH-cam studio app is rubbish and keeps hiding comments.
Hi Mr Murray, I dont really understand why youre allowed to use moles instead of concentration, when using the Ka formula? Please could you rephrase your explanation as I am quite lost. Thanks
Hi, very sorry, I missed your comment until just now. When I rearrange the Ka expression as a subject of [H+] for a buffer, I find myself with the [HA] on the top (numerator) and the [A-] on the bottom (denominator). They are both concentration terms which mean they are both 'moles divided by volume'. Since they are in the same solution, these volume terms would be the same (and cancel out) so I can leave them out and just use moles instead.
Hi sir I'm doing ocr paper 1 monday, am pretty confident on most topics except transition metals... I dont really understand how to know some of the products and equations even after watching videos. Could you do a video on transition metal questions and explainig them for ocr?
Hi, here are some suggestions for you in case you missed them ... This video covers all of the copper equations = th-cam.com/video/MEeDIN2Mmz8/w-d-xo.html This video covers iron and manganese equation = th-cam.com/video/KXi8M-ecwA0/w-d-xo.html this video covers some transition metal exam questions = th-cam.com/video/q9O6FxkjXVM/w-d-xo.html HAPPY REVISING!
I’m glad that I found your channel as there aren’t many chemistry teachers that are ocr specific and explain things clearly.
I’m very glad you’re finding it useful! Good luck in your exams 👏
This is such a good video, I appreciate the way you explain your thought process of each step and detail the method and reasoning as that’s where I struggle the most with deciphering mark schemes.
amazing video. youre the best chemistry teacher i have encountered by FAR!
quick question... the questions that you mentioned at 9:16, did you do an exam question walkthrough on this on you yt channel?
Thank you very much - I’m in the process of doing walkthroughs of all the MCQs in the exam papers (posted one today and there are some breadth in chem papers done already)
I met a girl at the UOM open day who recommended your channel to me, was not disappointed! she said she was one of your past students, can't remember her name though!
amazing! welcome to the channel
Awesome
Great video
Thanks!
cheeky sods giving that as a one marker
could not agree more. Similar for Hess cycle questions!
hello, i also have another question if you may... ocr only does acidic buffer calculations, not alkali right?
Only OCR B does weak base buffers - OCR A doesn’t 👍🏻
Do you still use square brackets when writing the expressions even though u use the mole values?
Hi, once you’ve started the calculation it won’t matter what brackets you use. Just make sure when writing the initial Ka (or Kc) expression you use square ones
Thank you, this was really helpful. For the last question, why is it quicker to use moles, isn’t the concentration already stated in the question?
Hi, the concentrations started in the question are not valid for the buffer as when you mix the two solutions together the total volume will change which would change each concentration (c = n/v). What you would need to do is re-calculate the adjusted concentrations to account for the change in the total volume now that the solutions are merged. Since this takes time and the volume terms would cancel out anyway, it is easier just to use moles.
@@mrmurraygreen Hey great video! Although, in the first question it says that “the student assumes that the volume of the solution does not change”. Does that mean we could have just plugged in the concentration values into that equation rather than using moles as the total volume hasn’t changed?
Hi, but the sodium salt isn’t a concentration? It’s a mass. It needs converting into moles to be used. Also sorry for the slow reply, the TH-cam studio app is rubbish and keeps hiding comments.
@@mrmurraygreen I understand now, thank you
@@mrmurraygreen Oh right that’s true😂, thanks for the clarification :)
Hi Mr Murray,
I dont really understand why youre allowed to use moles instead of concentration, when using the Ka formula?
Please could you rephrase your explanation as I am quite lost.
Thanks
Hi, very sorry, I missed your comment until just now. When I rearrange the Ka expression as a subject of [H+] for a buffer, I find myself with the [HA] on the top (numerator) and the [A-] on the bottom (denominator). They are both concentration terms which mean they are both 'moles divided by volume'. Since they are in the same solution, these volume terms would be the same (and cancel out) so I can leave them out and just use moles instead.
Hi sir I'm doing ocr paper 1 monday, am pretty confident on most topics except transition metals... I dont really understand how to know some of the products and equations even after watching videos. Could you do a video on transition metal questions and explainig them for ocr?
Hi, here are some suggestions for you in case you missed them ...
This video covers all of the copper equations = th-cam.com/video/MEeDIN2Mmz8/w-d-xo.html
This video covers iron and manganese equation = th-cam.com/video/KXi8M-ecwA0/w-d-xo.html
this video covers some transition metal exam questions = th-cam.com/video/q9O6FxkjXVM/w-d-xo.html
HAPPY REVISING!
@@mrmurraygreen Oh right I'll give those videos a watch! Thanks very much
hi for q1 if i proved that the given solutions give us ph of 4.53 wold that be fine
If you’re struggling to get to the exact answer - check you are not rounding up some of your data too much.