_jess_here__
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Attachment 886248



how do I approach this kinda question
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Mr Wednesday
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(Original post by _jess_here__)
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how do I approach this kinda question
"Attachement not found", try putting the qestion into text form so its possible / easy for people to see it as a starting point .
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(Original post by Mr Wednesday)
"Attachement not found", try putting the qestion into text form so its possible / easy for people to see it as a starting point .
ah sorry so the question was when 3.00g of an anhydrous nitrate of a group 2 metal is decomposed 1.53 g of gas is produced what is the nitrate compound ?
1.berilliyum nitrate
2. calcium nitrate
3. Magnesium nitrate
4. strontium nitrate
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Mr Wednesday
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(Original post by _jess_here__)
ah sorry so the question was when 3.00g of an anhydrous nitrate of a group 2 metal is decomposed 1.53 g of gas is produced what is the nitrate compound ?
1.berilliyum nitrate
2. calcium nitrate
3. Magnesium nitrate
4. strontium nitrate
Ok, 1st part, write down structures for each of those compunds, e.g. Be (NO3)2 etc. 2nd part, work out atomic mass of the molecule - be creatively lazy here, only work out the mass of (NO3)2 once . 3rd part, work out what fraction of a 3g mass of each compound is composed of nitrogen and oxygen.
Last edited by Mr Wednesday; 6 months ago
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gongoozled goose
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(Original post by Mr Wednesday)
Ok, 1st part, write down structures for each of those compunds, e.g. Be (NO3)2 etc. 2nd part, work out atomic mass of the molecule - be creatively lazy here, only work out the mass of (NO3)2 once . 3rd part, work out what fraction of a 3g mass of each compound is composed of nitrogen.
But we don't know the RFM of M(NO3)2
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gongoozled goose
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(Original post by _jess_here__)
ah sorry so the question was when 3.00g of an anhydrous nitrate of a group 2 metal is decomposed 1.53 g of gas is produced what is the nitrate compound ?
1.berilliyum nitrate
2. calcium nitrate
3. Magnesium nitrate
4. strontium nitrate
which metal does it show in mark scheme?
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Mr Wednesday
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(Original post by lyer_in_hellfyre)
But we don't know the RFM of M(NO3)2
You have a limited range of possibilities so start working from the top of the list down, and eliminate ones that are "impossible" until you find the unique one that fits.
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gongoozled goose
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(Original post by Mr Wednesday)
You have a limited range of possibilities so start working from the top of the list down, and eliminate ones that are "impossible" until you find the unique one that fits.
But how do we do that without knowing its moles? Do we take 1 because the stoichiometric equation says so?
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gongoozled goose
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(Original post by Mr Wednesday)
3rd part, work out what fraction of a 3g mass of each compound is composed of nitrogen.
Also i didnt get this... sorry and :ta: for your time...
what metal did you get? im getting as Sr

This is the method i used :
If 2.5 moles of total gases have 108g according to molar mass and balanced equation,
1.53g of total gases gives me...3.54E-2 moles of total gas formed.

If the ratio of metal oxide: total gases is 1 is to 2.5, after plugging the moles found frm above i get 1.41E-2 moles of metal oxide. I do know the mass of metal oxide (subtract mass of gases formed from 3g )
So now with moles and mass, i could find rfm of metal after subtracting molar mass of oxygen.
Last edited by gongoozled goose; 6 months ago
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_jess_here__
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(Original post by lyer_in_hellfyre)
which metal does it show in mark scheme?
A
(Original post by lyer_in_hellfyre)
which metal does it show in mark scheme?
berillium
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gongoozled goose
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(Original post by _jess_here__)
berillium
yikes how come :/
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_jess_here__
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(Original post by lyer_in_hellfyre)
yikes how come :/
uhh idek tis sucks
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gongoozled goose
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Pigster Deggs_14 any help in understanding the question is muchly appreciated! :ta: in advance!
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Deggs_14
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The thermal decomposition of a group 2 nitrate would decompose according to:
M(NO3)2 (s) —-> MO (s) + 4NO2 (g) + O2 (g). This is the first thing you should write.

Then I would work out (1.53/3.00) x 100 = 51%. So 51% gas is produced by mass.
Then work out the atom economy of the general decomposition formula using each group 2 ion, and see which group 2 metal.

The Mr of Sr(NO3)2 is 211.6 and the Mr of 4NO2 + O2 = 216. So these Mr values will make the 49/51% Mr ratio we’re interested in.
Hence the answer is Strontium.

The most common way to answer the question is just simply trial and error, there are only several group 2 metals, so just substitute their different Mr values until you find the one that works.
Last edited by Deggs_14; 6 months ago
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gongoozled goose
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(Original post by Deggs_14)
The thermal decomposition of a group 2 nitrate would decompose according to:
M(NO3)2 (s) —-> MO (s) + 4NO2 (g) + O2 (g). This is the first thing you should write.

Then I would work out (1.53/3.00) x 100 = 51%. So 51% gas is produced by mass.
Then work out the atom economy of the general decomposition formula using each group 2 ion, and see which group 2 metal.

The Mr of Sr(NO3)2 is 211.6 and the Mr of 4NO2 + O2 = 216. So these Mr values will make the 49/51% Mr ratio we’re interested in.
Hence the answer is Strontium.

The most common way to answer the question is just simply trial and error, there are only several group 2 metals, so just substitute their different Mr values until you find the one that works.
:ta: for reconfirming and detailed explanation!
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gongoozled goose
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(Original post by _jess_here__)
uhh idek tis sucks
The answer frm mark scheme is wrong :/
Last edited by gongoozled goose; 6 months ago
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