Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: aaa777 on April 21, 2008, 06:53:45 AM
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once again, i don't know where to start in solving this problem. i'm hoping you could give the steps or at least the first one?
Given:
A compound of the element A and oxygen has a mole ration of A:O = 2:3. If 8.0 grams of the oxide contains 2.4 grams of the oxygen, what is the atomic weight of A?
i'll be waiting for your reply. thank you very much.:)
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When we write a compound, like H2O or Fe2O3, we use a set of units, that are understood (that is to say implied and not mentioned.) What are those units? Hint: They're mentioned in your problem, elsewhere. Later in your problem, you're given the amount of oxygen, in grams. You simple have to convert the units. Well, convert units, and understand what I just said, to know why we convert units.
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Reascale problem from 2.4 g to 3 x 16 g (times 20)
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When we write a compound, like H2O or Fe2O3, we use a set of units, that are understood (that is to say implied and not mentioned.) What are those units? Hint: They're mentioned in your problem, elsewhere. Later in your problem, you're given the amount of oxygen, in grams. You simple have to convert the units. Well, convert units, and understand what I just said, to know why we convert units.
it's atomic mass unit right? what happens after converting 2.4 grams to amu? how do i get the atomic weight of element A from there? i believe the 8 grams that was given is not the formula weight of the compound. right?
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Reascale problem from 2.4 g to 3 x 16 g (times 20)
where did 20 come from? why do i need to do this step?
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what happens after converting 2.4 grams to amu?
You'll have to determine yourself, what that conversion means. So you'll be able to do it next time on your own.
how do i get the atomic weight of element A from there? i believe the 8 grams that was given is not the formula weight of the compound. right?
That's correct, you have more than one conversion to do
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Reascale problem from 2.4 g to 3 x 16 g (times 20)
where did 20 come from? why do i need to do this step?
Your compound contains 3 oxygen atoms which corresponds to 3x16 = 48 grams od oxygen. In your 8 grams sample you have 2.4 grams of oxygens - divide 48 by 2.4
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what happens after converting 2.4 grams to amu?
You'll have to determine yourself, what that conversion means. So you'll be able to do it next time on your own.
how do i get the atomic weight of element A from there? i believe the 8 grams that was given is not the formula weight of the compound. right?
That's correct, you have more than one conversion to do
i'm sorry but i can't really figure out what to do from there. i did the conversions of both the 8 gram sample of the compound and the 2.4 gram oxygen but i don't see how that will lead me to the atomic weight of element A. more hints?
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Reascale problem from 2.4 g to 3 x 16 g (times 20)
where did 20 come from? why do i need to do this step?
Your compound contains 3 oxygen atoms which corresponds to 3x16 = 48 grams od oxygen. In your 8 grams sample you have 2.4 grams of oxygens - divide 48 by 2.4
are these steps the same with what arckon's giving? could you please elaborate why i need to perform these?
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are these steps the same with what arckon's giving? could you please elaborate why i need to perform these?
No, I'm trying to be more subtle, and general, so you can solve problems other than this specific one. Follow AWK:'s advice this time, then try to see where I was coming from, so you can do the next problem.
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You have a sample A oxide with a ratio of 2:3 i.e. A2O3.
8g of A2O3 contains 2.4g of O.
How many grams of A are in 8g of A2O3?
2.4g of oxygen is how many moles?
If there are that many moles of O in 8g of A2O3 how many moles of A are there?
Once you have the number of moles and the mass in grams of A you can work out the molecular mass.