A-level chemistry ionic equations help!

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username3658760
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#1
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Hi, how can you tell what a solid is in the reaction between ionic compounds. For example:

1) when aqueous magnesium chloride is added to aqueous silver nitrate, a white precipitate is formed.
Write out the full stoichiometric and ionic equations for the reaction.
The answer is: mgcl2(aq) + 2agno3 (ag) = mg (no3)2 (ag) + 2agcl (s).

I'm very confused because how did we know that the solid formed was silver chloride and not magnesium nitrate??? Is there a way to figure out what the precipitate (s) will be because I asked my teacher and she said no, you just 'know'. But how the **** in an exam are you supposed to know what the aqueous will be and what the solid formed will be. She said in this particular reaction that nitrate is always dissolves in solution so that's how you know that won't be a solid.

But other questions give you compounds like: barium chloride and sodium sulphate, what is the solid formed and how do you know that?

Thanks
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sarah99630
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(Original post by TSR69)
Hi, how can you tell what a solid is in the reaction between ionic compounds. For example:
1) when aqueous magnesium chloride is added to aqueous silver nitrate, a white precipitate is formed.
Write out the full stoichiometric and ionic equations for the reaction.
The answer is: mgcl2(aq) + 2agno3 (ag) = mg (no3)2 (ag) + 2agcl (s).

I'm very confused because how did we know that the solid formed as silver chloride and not magnesium nitrate??? Is there a way to figure out what the precipitate (s) will be because I asked my teacher and she said no, you just 'know'. But how the **** in an exam are you supposed to know what the aqueas will be and what the solid formed will be. She said in this particular reaction that nitrate is always dissolves in solution so that's how you know that won't be a solid. But other questions give you compunds like: barium chloride and sodium sulphate, what is the solid formed and how do you know that?
Thanks
you need to know which ones are soluble, there was a table showing that in the edexcel AS book I think, u can come up with a mnemonic to help u remember. eg all nitrates are soluble, and I think everything with potassium, lithium and sodium are always soluble as well. most compounds may have 2 or 3 exceptions so it will be easy to remember. eg all chlorides are soluble except with 2 or 3 metals (I forgot which ones, I guess lead and silver??) try to look for that table. hopefully it'll make sense. good luck!
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ambershell27
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Is the topic qualitative analysis? Your teacher is right.
To summarize the precipitate reactions:
When testing for sulfate ions, add aqueous barium ions. A white precipitate of barium sulfate forms.
When testing for halide ions, add aqueous silver ions. A precipitate of silver halide forms.

If you've covered sequence of tests, carbonates also precipitate barium, and sulfate precipitates with silver ions. It's just something you have to learn.
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username3658760
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(Original post by sarah99630)
you need to know which ones are soluble, there was a table showing that in the edexcel AS book I think, u can come up with a mnemonic to help u remember. eg all nitrates are soluble, and I think everything with potassium, lithium and sodium are always soluble as well. most compounds may have 2 or 3 exceptions so it will be easy to remember. eg all chlorides are soluble except with 2 or 3 metals (I forgot which ones, I guess lead and silver??) try to look for that table. hopefully it'll make sense. good luck!
Oh no, I have to memorise them , thanks anyway
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username3658760
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(Original post by ambershell27)
Is the topic qualitative analysis? Your teacher is right.
To summarize the precipitate reactions:
When testing for sulfate ions, add aqueous barium ions. A white precipitate of barium sulfate forms.
When testing for halide ions, add aqueous silver ions. A precipitate of silver halide forms.

If you've covered sequence of tests, carbonates also precipitate barium, and sulfate precipitates with silver ions. It's just something you have to learn.
We haven't even touched on that, we just got introduced to it with no background info about how to know what the solid is in the product reaction, so it was guess work. We just got a sheet and miss told us to guess what the solid would be.
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ambershell27
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So she just expected you to remember from GCSE? Will you be doing more of the topic in class?
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username3658760
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(Original post by ambershell27)
So she just expected you to remember from GCSE? Will you be doing more of the topic in class?
We never learned it at GCSE (I did double science so I don't know if the others in my class did it at triple?), but yh she told us to 'guess' what the solid will be. She said that we'd go over it properly another time?, so you can't blame me if I haven't learned it yet
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ambershell27
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Ah, I see. That's an odd task to do if you have no previous knowledge, but if you're going to cover it later, then that's good.
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#9
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(Original post by ambershell27)
Ah, I see. That's an odd task to do if you have no previous knowledge, but if you're going to cover it later, then that's good.
Yh thanks you anyway amber
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