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Topic: Grade 11 exam review question (dillution, find known substance)?  (Read 11548 times)

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Offline djay230

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #15 on: January 19, 2012, 12:03:13 AM »
The calcium compound that is 'insoluble' is the precipitate.

going to bed in 10 minutes, i have no idea what solubility is...or a insoluble

can someone please explain how the chart works? no idea looking at it how anything works...

i do see the sulfate, dont see acetone

really confused, am i looking for sodium acetate, sodium nitrate, sodium sulphate to be insoluble or

sodium chloride, calcium sulfate? i really have no idea, so many possible combinations what am i looking for...

Offline djay230

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #16 on: January 19, 2012, 12:11:19 AM »
The calcium compound that is 'insoluble' is the precipitate.

going to bed in 10 minutes, i have no idea what solubility is...or a insoluble

can someone please explain how the chart works? no idea looking at it how anything works...

i do see the sulfate, dont see acetone

really confused, am i looking for sodium acetate, sodium nitrate, sodium sulphate to be insoluble or

sodium chloride, calcium sulfate? i really have no idea, so many possible combinations what am i looking for...

nvm, i found a table that makes sense...

ok so i understand that acetone and nitrate are apparently "soluable"
i think that means it will dissolve, therefore those 2 cannot be the unknown solution since it would not give me a precipitate but a solution.

Therefore the sodium sulphate must be the unknown because when mixed with calcium it is low soluable .

dont know if that means its still a liquid or not but low soluble sounds better than soluble.

 

also, with the mass of the precipitate, what can i do with that?

i used 100ml of the cacl, and 50ml of the sodium sulphate, the total mass of the precipitate would be what?

also, can anyone help me with a balanced equation for this?


cacl2 + NaSO4 ----> CaSO4 + NaCl2 ???

i am really bad at chem,

Offline djay230

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #17 on: January 19, 2012, 12:47:46 AM »
The calcium compound that is 'insoluble' is the precipitate.

going to bed in 10 minutes, i have no idea what solubility is...or a insoluble

can someone please explain how the chart works? no idea looking at it how anything works...

i do see the sulfate, dont see acetone

really confused, am i looking for sodium acetate, sodium nitrate, sodium sulphate to be insoluble or

sodium chloride, calcium sulfate? i really have no idea, so many possible combinations what am i looking for...

nvm, i found a table that makes sense...

ok so i understand that acetone and nitrate are apparently "soluable"
i think that means it will dissolve, therefore those 2 cannot be the unknown solution since it would not give me a precipitate but a solution.

Therefore the sodium sulphate must be the unknown because when mixed with calcium it is low soluable .

dont know if that means its still a liquid or not but low soluble sounds better than soluble.

 

also, with the mass of the precipitate, what can i do with that?

i used 100ml of the cacl, and 50ml of the sodium sulphate, the total mass of the precipitate would be what?

also, can anyone help me with a balanced equation for this?


cacl2 + NaSO4 ----> CaSO4 + NaCl2 ???

i am really bad at chem,


mhh gonna check this in the morning

but i beielve it is

cacl2 + na2so4 -----> caso4 + 2nacl

hope its right, and for anyone else out there that can tell me what the mass of the precipitate can be used for i'd gladly appreciate it...

feeling better from my sickness dont know if i'll go to school tomorrow,  have a fever but atleast i learned what i need to for my exam

so if anyone can tell me if a question can be used with the mass of the precipitate or if the whole purpose of this was to understand that precipitate was formed which meant it had to be a unknown solution of sodium sulphate....


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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #18 on: January 19, 2012, 05:12:16 AM »
You got it generally right - if there was a precipitate (solid appearing in the resulting solution after solutions were mixed), something was insoluble - and the only insoluble substance that can produced here (as you checked using solubility rules) is a calcium sulfate. As your solution of the calcium chloride already contained calcium ions, it was apparently mixed with a solution containing sulfate ions, and calcium sulfate precipitated out of the solution.

You listed volumes of the solutions that were mixed - do you know concentrations? If so, you can try to use stoichiometry to calculate how much precipitate should be produced. That's where the masses come into the question. If the real mass of the precipitate is close to the calculated mass of calcium sulfate, that's additional confirmation that you are right.

But I don't expect it to be similar (which still doesn't mean you are wrong). There are several other factors that should be taken into account here. I doubt you know these factors yet.
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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #19 on: January 19, 2012, 05:16:18 AM »
Quote
As Arkcon said above, try to write down the chemical equations.

Sorry guys, but asking djay to start with reaction equations was completely off. UG was right pointing at solubility rules - not knowing nor understanding these it is pointless to start writing reactions, as you can't predict products.
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Offline djay230

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #20 on: January 19, 2012, 09:19:52 AM »
You got it generally right - if there was a precipitate (solid appearing in the resulting solution after solutions were mixed), something was insoluble - and the only insoluble substance that can produced here (as you checked using solubility rules) is a calcium sulfate. As your solution of the calcium chloride already contained calcium ions, it was apparently mixed with a solution containing sulfate ions, and calcium sulfate precipitated out of the solution.

You listed volumes of the solutions that were mixed - do you know concentrations? If so, you can try to use stoichiometry to calculate how much precipitate should be produced. That's where the masses come into the question. If the real mass of the precipitate is close to the calculated mass of calcium sulfate, that's additional confirmation that you are right.

But I don't expect it to be similar (which still doesn't mean you are wrong). There are several other factors that should be taken into account here. I doubt you know these factors yet.

Does anyone know how to find the limiting reagent of

Cacl2 + na2SO4 -----> caso4 + 2nacl

For caso4?

I cannot find it :(
Help please !


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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #21 on: January 19, 2012, 09:33:27 AM »
Does anyone know how to find the limiting reagent of

Cacl2 + na2SO4 -----> caso4 + 2nacl

For caso4?

What you wrote suggests you have no idea what the limiting reagent is. You need to know amounts of both reacting substances to be able to say which one is a limiting reagent. For a given reaction equation it is not always the same substance.

See

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

and

http://www.chembuddy.com/?left=balancing-stoichiometry&right=limiting-reagents
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Offline djay230

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #22 on: January 19, 2012, 10:06:07 AM »
Does anyone know how to find the limiting reagent of

Cacl2 + na2SO4 -----> caso4 + 2nacl

For caso4?

What you wrote suggests you have no idea what the limiting reagent is. You need to know amounts of both reacting substances to be able to say which one is a limiting reagent. For a given reaction equation it is not always the same substance.

See

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

and

http://www.chembuddy.com/?left=balancing-stoichiometry&right=limiting-reagents


Cacl2 + naso4 ---->2nacl + caso4

How do you find it :(

I need to know how to find limiting reagent and not to read on balancing equations



I only have the mass of caso4 how would I use that ?

If I have the concentration how would I use that?


Offline fledarmus

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #23 on: January 19, 2012, 11:23:20 AM »
It's time to use some logic...

1) Do you know the concentration of the CaCl2 that was in your starting solution?

2) Can you use this information to find the total moles of calcium that you added?

3) From your balanced chemical reaction, do you know what physical state each of the four components would be in your final mixture?

4) Do you know the concentration of the unknown salt? (My guess is that this answer is "no", but if it is "yes", skip the next question and solve as a limiting reagent question.)

5) From the amount of calcium that you added, can you estimate a range of masses for the solid that you might expect, based on different values for the concentration of the unknown salt?

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #24 on: January 19, 2012, 11:38:45 AM »
I need to know how to find limiting reagent and not to read on balancing equations

Sigh. Neither of the pages linked to talks about balancing equations. Apparently you have not even visited them.
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Offline djay230

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Re: Grade 11 exam review question (dillution, find known substance)?
« Reply #25 on: January 19, 2012, 04:26:32 PM »
It's time to use some logic...

1) Do you know the concentration of the CaCl2 that was in your starting solution?

2) Can you use this information to find the total moles of calcium that you added?

3) From your balanced chemical reaction, do you know what physical state each of the four components would be in your final mixture?

4) Do you know the concentration of the unknown salt? (My guess is that this answer is "no", but if it is "yes", skip the next question and solve as a limiting reagent question.)

5) From the amount of calcium that you added, can you estimate a range of masses for the solid that you might expect, based on different values for the concentration of the unknown salt?


thanks for giving me a detailed answer but i took the exam today, it was okay i think i messed up on some of the questions that was based on vocabulary. Really appreciate you being one of the very few people that gave a valid response to my questions and frustrations.

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