I’m kind of confused with the multiplying of the avagadros constant as I’ve been taught to divide by 1000 then divide by avagadros constant when finding the mass of one ion but you multiply it ?
The way I go about these types of questions is that I always think of the units. For example, I would look at: Mass number as g/mol (or g mol^-1) Avogadro's constant as 1/mol (or mol^-1) Now, say for instance, we have a question that is telling us to find the mass of a single 52Cr+ ion, where the mass of the ion is the same as the 52Cr atom. The steps to work it out would be; Step 1: The 52Cr atom has a mass number of 52. I look at that and think "with the units the value is 52 g/mol, as its the mass number" Step 2: I would divide by Avogadro's constant which is mol^-1 (this is because I want to find grams, and the value I have from step 1 is g/mol. Think about the units - if we divide g/mol with mol^-1 (1/mol), we will be left with g only.) Step 3: After dividing 52 g/mol with 6.022x10^23 mol^-1, we will be left with 8.64x10^-23 grams. We then turn this into Kg for the answer. Conversely, If we had Kg and wanted to find out mass number (such as the question in the video), the steps would be as follows: Step 1: We start with 8.97x10^-26 Kg. Turn into grams which leaves us with 8.97x10^-23 g. Step 2: Since we are looking for g/mol (units for mass number) we do 8.97x10^-23 g x 6.022x10^23 mol^-1 (Avogadro's constant). Once again, if you look at the units, g x mol^-1 gives us g mol^-1 (or g/mol - the units for mass number). Step 3: The calculation would give us 54.01734 g/mol. Round to the nearest whole number and you get a mass number of 54 g/mol. I hope this explanation made some sense to you, as its kind of difficult to explain.
Whether you divide or multiply by 1,000 depends on whether you're starting or finishing with the mass number. The vast majority of questions start with the mass number of the ion e.g. Chlorine-37. This tells you the mass of one mole of chlorine-37 ions = 37g/mol. Because the kinetic energy equation has mass in kg, you need to divide by 1,000 to turn the molar mass into kg/mol. You can then divide this by Avogadro's number to get the mass of one ion in kg. However, in this question, you're having to finish with the mass number. In effect, you're working backwards compared with the usual question. So, you calculate the mass on a single ion in kg using the kinetic energy equation. You multiply by Avogadro's number to get the mass of a mole of these ions in kg. You finally multiply by 1,000 to get the mass of a mole in g. The final mass number must be an integer so you round accordingly. I hope this helps.
All you need to understand is the fact that you've just calculated the mass of a single ion (variant form of an atom). As mass number is the mass of 1 mole of that atom / ion, we multiply our mass of that single ion by avogadros constant (no.atoms in 1 mole) to obtain the mass of a 1 mole of that ion. Then convert from Kg to g to obtain correct value for mass number :)
Why did you multiply the weight by avagadros constant, I read that on persons comment is that the Mr you calculated cos u only put the symbol kg. I'm so confused , I thought you could only multiply the number of moles by avagadros constant to find the total number of particles
I try to explain why in the video. Using the TOF equations, I am able to calculate the mass, in kg, of a single ion. But I have to work out the mass number, which is also the mass in grams of a mole of those ions. So I multiply by Avogadro's constant to work out the mass of a mole of ions in kg and then by a 1,000 to convert this into g. In this question, you're working in reverse to how you normally would. You typically start with a mass number e.g. Br-79 and then work out the mass of one [Br-79]+ ion by dividing 79 by 1,000 (to convert it to kg) and then by avogadro's constant. In this question, you have to go the other way. It would help me understand your question better if you said what you think I should have done.
You’re a real one, thank you
nice video, thanks man
I’m kind of confused with the multiplying of the avagadros constant as I’ve been taught to divide by 1000 then divide by avagadros constant when finding the mass of one ion but you multiply it ?
The way I go about these types of questions is that I always think of the units.
For example, I would look at:
Mass number as g/mol (or g mol^-1)
Avogadro's constant as 1/mol (or mol^-1)
Now, say for instance, we have a question that is telling us to find the mass of a single 52Cr+ ion, where the mass of the ion is the same as the 52Cr atom. The steps to work it out would be;
Step 1: The 52Cr atom has a mass number of 52. I look at that and think "with the units the value is 52 g/mol, as its the mass number"
Step 2: I would divide by Avogadro's constant which is mol^-1 (this is because I want to find grams, and the value I have from step 1 is g/mol. Think about the units - if we divide g/mol with mol^-1 (1/mol), we will be left with g only.)
Step 3: After dividing 52 g/mol with 6.022x10^23 mol^-1, we will be left with 8.64x10^-23 grams. We then turn this into Kg for the answer.
Conversely,
If we had Kg and wanted to find out mass number (such as the question in the video), the steps would be as follows:
Step 1: We start with 8.97x10^-26 Kg. Turn into grams which leaves us with 8.97x10^-23 g.
Step 2: Since we are looking for g/mol (units for mass number) we do 8.97x10^-23 g x 6.022x10^23 mol^-1 (Avogadro's constant). Once again, if you look at the units, g x mol^-1 gives us g mol^-1 (or g/mol - the units for mass number).
Step 3: The calculation would give us 54.01734 g/mol. Round to the nearest whole number and you get a mass number of 54 g/mol.
I hope this explanation made some sense to you, as its kind of difficult to explain.
Whether you divide or multiply by 1,000 depends on whether you're starting or finishing with the mass number.
The vast majority of questions start with the mass number of the ion e.g. Chlorine-37. This tells you the mass of one mole of chlorine-37 ions = 37g/mol. Because the kinetic energy equation has mass in kg, you need to divide by 1,000 to turn the molar mass into kg/mol. You can then divide this by Avogadro's number to get the mass of one ion in kg.
However, in this question, you're having to finish with the mass number. In effect, you're working backwards compared with the usual question. So, you calculate the mass on a single ion in kg using the kinetic energy equation. You multiply by Avogadro's number to get the mass of a mole of these ions in kg. You finally multiply by 1,000 to get the mass of a mole in g. The final mass number must be an integer so you round accordingly.
I hope this helps.
All you need to understand is the fact that you've just calculated the mass of a single ion (variant form of an atom). As mass number is the mass of 1 mole of that atom / ion, we multiply our mass of that single ion by avogadros constant (no.atoms in 1 mole) to obtain the mass of a 1 mole of that ion. Then convert from Kg to g to obtain correct value for mass number :)
@@Diapt BRUH UR AMAZING USING THE UNITS MAKES SO MUCH MORE SENSE.THANK YOU!
@@Diaptty
Hi, is there any reason you didn’t include the decimals whilst calculating the velocity?
Good video dude
Appreciate it
Why did you multiply the weight by avagadros constant, I read that on persons comment is that the Mr you calculated cos u only put the symbol kg. I'm so confused , I thought you could only multiply the number of moles by avagadros constant to find the total number of particles
I try to explain why in the video. Using the TOF equations, I am able to calculate the mass, in kg, of a single ion. But I have to work out the mass number, which is also the mass in grams of a mole of those ions. So I multiply by Avogadro's constant to work out the mass of a mole of ions in kg and then by a 1,000 to convert this into g.
In this question, you're working in reverse to how you normally would. You typically start with a mass number e.g. Br-79 and then work out the mass of one [Br-79]+ ion by dividing 79 by 1,000 (to convert it to kg) and then by avogadro's constant. In this question, you have to go the other way.
It would help me understand your question better if you said what you think I should have done.
please may i have a pdf version of this document ?
It’s off a freely available AQA past paper but I’m afraid I can’t remember which one. Sorry.
Thank you so much ❤❤
You're welcome 😊