# Chemistry question help!!

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#1
Hello, i am currently transitioning from Y11 to Y12 and have a question on something. Am I right in saying that the mass of a 1H atom is 1/6.022x10^23, in other words... 1.66057781 because mass of an atom = Ar of element / Avogadro constant? and the mass of one mol of 3 H atoms is 1.660 etc from earlier multiplied by Avogadro's constant to get 1? Could I also just use mass = mol x Mr to work out 1 mol x the Mr of 3H which is just 1? 1x1 = 1? Then what about the mass of a H+ ion? is it just the mass of a proton? eg: 1.6726x10^-24?
Last edited by absterlmao1; 4 weeks ago
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4 weeks ago
#2
(Original post by absterlmao1)
Hello, i am currently transitioning from Y11 to Y12 and have a question on something. Am I right in saying that the mass of a 1H atom is 1/6.022x10^23, in other words... 1.66057781 because mass of an atom = Ar of element / Avogadro constant? and the mass of one mol of 3 H atoms is 1.660 etc from earlier multiplied by Avogadro's constant to get 1? Could I also just use mass = mol x Mr to work out 1 mol x the Mr of 3H which is just 1? 1x1 = 1? Then what about the mass of a H+ ion? is it just the mass of a proton? eg: 1.6726x10^-24?
The mass of a H+ atom is the mass of a proton because it is just a proton. You seem to have some equations mixed up which is why I understand your confusion.

mass = moles x Mr
number of particles = moles x Avogadro's constant
moles = concentration x volume.

You weren't working out the mass of the hydrogen ion, you seem to have been trying to work out the number of particles but your equations were mixed. I suggest taking it step by step. If need be, you can post another question.

Just remember that A-Level Chemistry is a huge jump from GCSE. Mark schemes are so much more specific, there are more topics and the one thing that needs to be done before you think about that is to go through what you learnt at GCSE because that is your knowledge base for AS and A2.

Do not fret about the big jump because everyone initially struggles - I did but I overcame that and I ended up getting a B in my AS exam! (highest grade you can get at AS is an A) - Just don't stress too much, print out the specification, do some background reading - most of the moles calculations are the same so you can practice those first!
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#3
Thank you!
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2 weeks ago
#4
(Original post by absterlmao1)
Hello, i am currently transitioning from Y11 to Y12 and have a question on something. Am I right in saying that the mass of a 1H atom is 1/6.022x10^23, in other words... 1.66057781 because mass of an atom = Ar of element / Avogadro constant? and the mass of one mol of 3 H atoms is 1.660 etc from earlier multiplied by Avogadro's constant to get 1? Could I also just use mass = mol x Mr to work out 1 mol x the Mr of 3H which is just 1? 1x1 = 1? Then what about the mass of a H+ ion? is it just the mass of a proton? eg: 1.6726x10^-24?
@JA03 has already answered this very competently, but I reckon I can give further assistance.

Dividing the relative mass of a species by Avogadro’s constant gives you the mass of a single particle in grams. There was actually a GCSE exam question (Q9e) in Edexcel’s june 2018 paper 1 (triple higher) where you had to use this method.

Dimensionally (i.e in terms of units) this works, as the units of relative mass are g/mol and the units of Avogadro’s constant are 1/mol:

(g/mol) / (1/mol) = g/mol x mol = g

So the mass of a single 1H atom in grams can be estimated using such a method, as the relative mass of 1H is 1 g/mol.

The mass of 1 mole of 3H atoms is actually 3 grams. This is because the relative mass of 3H is 3 g/mol (hence the 3). We can again check this dimensionally:

3 g/mol x 1 mol = 3 g

The difference between 1H and 3H is that 3H contains two neutrons (which add mass) and 1H has no neutrons. Both however, contain 1 proton, as they are isotopes.

And yes, it is reasonable to assume that a H+ ion does have an identical mass to a proton.
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#5
(Original post by TypicalNerd)
@JA03 has already answered this very competently, but I reckon I can give further assistance.

Dividing the relative mass of a species by Avogadro’s constant gives you the mass of a single particle in grams. There was actually a GCSE exam question (Q9e) in Edexcel’s june 2018 paper 1 (triple higher) where you had to use this method.

Dimensionally (i.e in terms of units) this works, as the units of relative mass are g/mol and the units of Avogadro’s constant are 1/mol:

(g/mol) / (1/mol) = g/mol x mol = g

So the mass of a single 1H atom in grams can be estimated using such a method, as the relative mass of 1H is 1 g/mol.

The mass of 1 mole of 3H atoms is actually 3 grams. This is because the relative mass of 3H is 3 g/mol (hence the 3). We can again check this dimensionally:

3 g/mol x 1 mol = 3 g

The difference between 1H and 3H is that 3H contains two neutrons (which add mass) and 1H has no neutrons. Both however, contain 1 proton, as they are isotopes.

And yes, it is reasonable to assume that a H+ ion does have an identical mass to a proton.
This is a perfect response thank you so much I understand now. Bringing the units into it made it a lot clearer. As for the exam question, I didn't do triple science I did the single IGCSE Chemistry so these kinds of questions to do with Avogadro's number are completely new to me. Thanks again.
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2 weeks ago
#6
(Original post by absterlmao1)
This is a perfect response thank you so much I understand now. Bringing the units into it made it a lot clearer. As for the exam question, I didn't do triple science I did the single IGCSE Chemistry so these kinds of questions to do with Avogadro's number are completely new to me. Thanks again.
My best advice for A level chemistry is use dimensional analysis as you are doing the question. There’s nothing worse than getting a wrong answer when you notice something went wrong with the units along the way.
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2 weeks ago
#7
(Original post by absterlmao1)
This is a perfect response thank you so much I understand now. Bringing the units into it made it a lot clearer. As for the exam question, I didn't do triple science I did the single IGCSE Chemistry so these kinds of questions to do with Avogadro's number are completely new to me. Thanks again.
Adding onto what TypicalNerd said, when doing A-Level Chemistry, looking at units, key words in the question and the number of marks can give an idea of what you need to do to answer the questions. The questions are usually repetitive so it’s all about practicing past paper questions! My best advice is past paper questions and highlighting key words and numbers so you get an idea of what you need to do.
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