Time of flight mass spectrometer calculations
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- Опубліковано 8 бер 2020
- This video takes you through how to rearrange the formula for kinetic energy to give velocity, and then how to use this in conjunction with knowing the length of the flight tube in calculating time of flight (and all the other variations). I also show you how to calculate the mass of a single ion from the isotope's molar mass.
If you are mathematically minded and can show how the equations are derived, brilliant! You need to be able to do this in examination questions.
If you are, like me, mathematically challenged, then spend some time studying how one equation comes from another, and memorise it - it's far easier in the long run.
😱 Correction for Q.1 - see photo of my notes on Google drive link for correct working and answer: drive.google.com/file/d/1Rind...
You can find notes and exam style questions on this at crunchchemistry.co.uk/time-of... 😀.
Please click link (Google drive photo) for correction to Q1 - huge apologies! 😊
drive.google.com/file/d/1RindprJmQOrq0t6-j95Ww9KSB5CqQs7U/view?usp=sharing
revisiting this video the night before my chem paper 1
Thanks I've been trying to understand TOF for ages my textbook has absolutely none of the calculations or even any of the formulas
I'm really pleased this video has ticked all the boxes - unfortunately your textbook is only ever going to give you an overview of any topic at A level, so you need to mine your teachers' / school / college expertise and past papers. There is a bank of TOF exam questions with detailed worked through answers at crunchchemistry.co.uk in the Atoms, Ions and Molecules unit 😊
@@CrunchChemistry thank you
What a helpful video. Thanks !
Hi, you should use unrounded values to calculate your answers and only round at the end because it effects the accuracy of your answer. With unrounded values aka accurate values I got 5.31*10^-6s
Absolutely - number one rule is not to round up to 2 or 3 sig fig during any calculation, but the settings on your calculator (as in to how many sig fig or decimal places it cuts off your calculations) also explains why answers may vary
Thank you so much! seriously the way you explain things really helped me understand.
thank you so much!!!
So helpful! Thank you
The key is to mastering this is practice - I know the text books are a bit useless on ToF calculations, so scour the past papers for questions.
thanks- super helpful!
I'm so pleased it helps 😊
thank you
appreciate the help thanks
And thanks for the feedback - go practice!
Hi, thanks for the video and I now fully understand TOF but, on the last question, could you explain to me how you were able to get a time of 5.23 x 10^-6 because I got 5.27 x 10^-, unless my answer as well is accepted?
So pleased you have got this sorted - I've gone back to my original video notes and I also have an answer of 5.268 x 10^-6s so another typo and another apology 😐
Hello, great video this has really helped me understand TOF calculations, in the last question I got 5.314747263 x 10^-16, ( rounded it up to 5.3 however ), I think this is due to me not rounding the numbers up until the end so will there be a range the answers is in?
You shouldn't round up until your final answer, then cut it off at the appropriate number of significant figures - your answer will be fine x 10^-6 not x10^-16? (it can depend slightly on calculator settings).
@@CrunchChemistry yeah I never round up until my final answer and oh yeah 10^-6 lol, thank you again!
thanks for saving me in my test gyal
You're welcome 🎉
Could you perhaps consider doing ionic equations?
Have a look in the atoms. ions and molecules playlist - there is one ready for you!
Can someone tell me how the mass calculation in the first question works
Where have I lost you specifically? Let me know and I'll work through it with you.
@@CrunchChemistry in the first one i worked out the mass the same way you did it and i ended up with a completely different number
@@joseaelizabeth4938 I'm so sorry, you are quite right, the mass should be 3.985 x 10-26kg from the Mg ion. See the link in the pinned comment for the working from my notes.
in a MS where a tof question is 3 marks why is the mass used for 49Ti + not 49/6.022x1023 /1000 but its just 49. so the answer for question is much bigger than mine
Sorry, I've only just seen this! I'd need to see the whole question but you've probably figured it out now.