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# who's good at chemistry? watch

1. http://www.ocr.org.uk/Images/131286-...and-groups.pdf 4Cii) help pls. for some reason for the answer the moles of ii) is half of the moles of i) but I don't see a 2:1 molar ratio in the balanced equation, what is going on. thanks.
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(Original post by Puddles the Monkey)
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3. (Original post by ronnydandam)
http://www.ocr.org.uk/Images/131286-...and-groups.pdf 4Cii) help pls. for some reason for the answer the moles of ii) is half of the moles of i) but I don't see a 2:1 molar ratio in the balanced equation, what is going on. thanks.
Peroxidation ??
4. Group 2 metal, hence the equation is of the chloride is XCl2, and therefore for each mole of that you must have 2 of AgCl to balance chlorines
5. I got the answer as Magnesium.
You work it from backwards. Ill post the pictures of my working tommorow? Im really sleepy and my phone needs to charge
6. (Original post by samb1234)
Group 2 metal, hence the equation is of the chloride is XCl2, and therefore for each mole of that you must have 2 of AgCl to balance chlorines
The moles of AgCl is 0.06. The moles of of the group 2 chloride is 0.03.
its a good question
7. (Original post by Neurology)
The moles of AgCl is 0.06. The moles of of the group 2 chloride is 0.03.
its a good question
I know
8. Wellp, you know it's a group 2 metal and therefore has a 2+ ion in the group 2 chloride salt. So that means there's 1 mole of the metal to every 2 moles of the chloride ions.

To work out the moles of chloride you just need to work out the moles of silver chloride, since there's a 1:1 mole ratio. So you do your mass over Mr to get 0.06 moles. Since there's 2 moles of chloride ions to every mole of the metal you divide this by 2 to give 0.03 moles of group 2 metal ions.

The next step is working out how many grams of chloride were in the original chloride sample. The silver nitrate was in excess so you can assume that all of the chloride reacted. So, since the Ar of chlorine is 35.5 (it's negligibly higher for chloride but that doesn't matter here, after all it's just 5.5x10-4g more) you multiply 0.06 by 35.5 to give you 2.13g of chloride ions.

So for the mass of the group 2 metal in the sample you do the mass of the sample - the mass of chloride ions, which comes to 0.73g. Obviously the metal's quite light so you can discard all of the heavier group 2 metals as possibilities, beryllium chloride is molecular so it can't be that either. Anyways, divide the metal's mass by the number of moles to get the Mr and then that tells you what the metal is.

I came out with 24.3, so Magnesium's your mystery metal.
9. (Original post by thefatone)
Peroxidation ??
(Original post by samb1234)
Group 2 metal, hence the equation is of the chloride is XCl2, and therefore for each mole of that you must have 2 of AgCl to balance chlorines
(Original post by Neurology)
I got the answer as Magnesium.
You work it from backwards. Ill post the pictures of my working tommorow? Im really sleepy and my phone needs to charge
(Original post by Neurology)
The moles of AgCl is 0.06. The moles of of the group 2 chloride is 0.03.
its a good question
(Original post by samb1234)
I know
(Original post by Peroxidation)
Wellp, you know it's a group 2 metal and therefore has a 2+ ion in the group 2 chloride salt. So that means there's 1 mole of the metal to every 2 moles of the chloride ions.

To work out the moles of chloride you just need to work out the moles of silver chloride, since there's a 1:1 mole ratio. So you do your mass over Mr to get 0.06 moles. Since there's 2 moles of chloride ions to every mole of the metal you divide this by 2 to give 0.03 moles of group 2 metal ions.

The next step is working out how many grams of chloride were in the original chloride sample. The silver nitrate was in excess so you can assume that all of the chloride reacted. So, since the Ar of chlorine is 35.5 (it's negligibly higher for chloride but that doesn't matter here, after all it's just 5.5x10-4g more) you multiply 0.06 by 35.5 to give you 2.13g of chloride ions.

So for the mass of the group 2 metal in the sample you do the mass of the sample - the mass of chloride ions, which comes to 0.73g. Obviously the metal's quite light so you can discard all of the heavier group 2 metals as possibilities, beryllium chloride is molecular so it can't be that either. Anyways, divide the metal's mass by the number of moles to get the Mr and then that tells you what the metal is.

I came out with 24.3, so Magnesium's your mystery metal.
Thanks to all of you, I really appreciate it! Sorry for being a pain!
10. (Original post by ronnydandam)
Thanks to all of you, I really appreciate it! Sorry for being a pain!
Nah, you're not being a pain. We all get stuck sometimes, it's far better to get help with it than to ignore it.
11. (Original post by Peroxidation)
Nah, you're not being a pain. We all get stuck sometimes, it's far better to get help with it than to ignore it.
It won't let me give a you a rep? :/ Thanks again anyway!
12. (Original post by Peroxidation)
Nah, you're not being a pain. We all get stuck sometimes, it's far better to get help with it than to ignore it.
word.

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