<![CDATA[Latest posts for the thread "Chemistry help"]]> http://www.dakkadakka.com/dakkaforum/posts/list/54.page JForum - http://www.jforum.net Chemistry help
1. What is the molarity of a solution made by dissolving 24.8 g of calcium hydroxide in 500.0 mL of water?

I figured out the first part by using 24.8 g of Ca(OH)2 x 1 mol/74.1 g = 0.336 mol of Ca(OH)2, c = n/v = 0.336 mol/0.5L = O.672 mol/L Ca(OH)2

2. What is the concentration of [OH-] in the solution prepared in question #1?

I get the first question but how do I do the second part?

]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635275.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635275.page GMT Chemistry help http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635292.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635292.page GMT Chemistry help http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635309.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635309.page GMT Chemistry help
I failed chemistry. I remember learning this right before I just gave up and started gakking around in class. That was a good year... ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635310.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635310.page GMT Chemistry help
The math is just to solid.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635313.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635313.page GMT Chemistry help
Calcium Hydroxide is extremely basic which means it disassociates completely in water which means per mole of CaOH2 there is one mole Ca and 2 moles of OH.

Not 42. Should be in the order of 1.3

]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635337.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635337.page GMT Chemistry help
Cheesecat wrote:I'm having trouble with two questions in chemistry.

1. What is the molarity of a solution made by dissolving 24.8 g of calcium hydroxide in 500.0 mL of water?

I figured out the first part by using 24.8 g of Ca(OH)2 x 1 mol/74.1 g = 0.336 mol of Ca(OH)2, c = n/v = 0.336 mol/0.5L = O.672 mol/L Ca(OH)2

2. What is the concentration of [OH-] in the solution prepared in question #1?

I get the first question but how do I do the second part?


You maths is fine too BTW, as I've looked up the masses and worked it out from scratch to check.

Haven't done that in years...

Got asked it in an interview once - "How would you make up a 0.5M solution of something". If you go into science, don't forget the basics.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635414.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635414.page GMT Chemistry help
Cheesecat wrote:I'm having trouble with two questions in chemistry.

1. What is the molarity of a solution made by dissolving 24.8 g of calcium hydroxide in 500.0 mL of water?

I figured out the first part by using 24.8 g of Ca(OH)2 x 1 mol/74.1 g = 0.336 mol of Ca(OH)2, c = n/v = 0.336 mol/0.5L = O.672 mol/L Ca(OH)2

2. What is the concentration of [OH-] in the solution prepared in question #1?

I get the first question but how do I do the second part?



Because Ca(OH)2 dissasociates completely in water, there would be 2 moles of [OH-] for every mole of Ca(OH)2, this means that there would be 1.344mol/L of [OH-].
you then convert the mol/L to g/L (which is equal to g/dm3), so you get 22.848g/dm3 of [OH-], which should be rounded to 22.8g/dm3, as the original information is only to 3 significant figures.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635433.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635433.page GMT Chemistry help
AustonT wrote:for every mole of Ca(OH)2 there will be two moles of OH-


So 0.672 mol/L x 2 mol OH-/1 mol Ca(OH)2 = 1.34 mol/L? ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635435.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635435.page GMT Chemistry help

Automatically Appended Next Post:
wait no...
CA+= 0.672 Mol/L and OH-=1.34 mol/L


Automatically Appended Next Post:
just drop the CA ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635449.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635449.page GMT Chemistry help http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635457.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635457.page GMT Chemistry help
AustonT wrote:Yes


Automatically Appended Next Post:
wait no...
CA+= 0.672 Mol/L and OH-=1.34 mol/L


Automatically Appended Next Post:
just drop the CA


Oh, OK thanks. ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635463.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635463.page GMT Chemistry help http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635465.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635465.page GMT Chemistry help
AustonT wrote:Are you going to have to do this on a test?


Final Exam.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635484.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635484.page GMT Chemistry help So without the numbers the CHEMICAL equation and knowing that this particular completely disassociates is key ( on your test it will too they wont curve ball a partial reaction over time if you haven't covered it).
So once you do the molar garbage for the solution they ask how much of one ion molar there is.
For this:
Ca(OH)2--> Ca and 2OH so you plug in
1x(total molar) and 2x (total molar)
or for lets pretend
WX2Y7Z
would be --->W 2X 7Y Z
(number) 2x(number) 7(number) (number0
When they ask for the ion though dont spit back the whole equation...you might be right but lose all of some of the points for that.
]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635507.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635507.page GMT Chemistry help
Or am i missing something]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635825.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635825.page GMT Chemistry help
frgsinwntr wrote:wait... doesn't the OH- concentration depend upon the temperature of the solution?

Or am i missing something


No, concentration is the amount per unit volume.


edited to add..

What you might be thinking of is where you put so much of a substance in that it can't all dissolve, so by heating it, you can get more to dissolve into solution. But of course the concentration is increasing because you are adding more of a solute to the solution.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635861.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635861.page GMT Re:Chemistry help
that's how I got through AP chemistry...]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635930.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3635930.page GMT Re:Chemistry help
WARORK93 wrote:Google it...

that's how I got through AP chemistry...

I wish I had had google to help me through AP Chem]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636209.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636209.page GMT Chemistry help http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636350.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636350.page GMT Chemistry help



I shoulda studied chemistry. Or Economics. Or anything but a humanities-based major.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636365.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636365.page GMT Chemistry help http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636625.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636625.page GMT Re:Chemistry help
It hurted.

]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636735.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636735.page GMT Chemistry help UK is 80% organic ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636762.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3636762.page GMT Chemistry help
Howard A Treesong wrote:
frgsinwntr wrote:wait... doesn't the OH- concentration depend upon the temperature of the solution?

Or am i missing something


No, concentration is the amount per unit volume.


edited to add..

What you might be thinking of is where you put so much of a substance in that it can't all dissolve, so by heating it, you can get more to dissolve into solution. But of course the concentration is increasing because you are adding more of a solute to the solution.


Agreed, that concentration is realted to the unit pervolume, however at higher temperature the energies present allow more more OH to break off and float freely within the material correct? Its been a while since i Had PhysChem.... I'll see if I can find it later]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637408.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637408.page GMT Chemistry help
frgsinwntr wrote:
Howard A Treesong wrote:
frgsinwntr wrote:wait... doesn't the OH- concentration depend upon the temperature of the solution?

Or am i missing something


No, concentration is the amount per unit volume.


edited to add..

What you might be thinking of is where you put so much of a substance in that it can't all dissolve, so by heating it, you can get more to dissolve into solution. But of course the concentration is increasing because you are adding more of a solute to the solution.


Agreed, that concentration is realted to the unit pervolume, however at higher temperature the energies present allow more more OH to break off and float freely within the material correct? Its been a while since i Had PhysChem.... I'll see if I can find it later


You assume for the question that it fully dissociates and that there is no undissolved material suspended in the liquid.

Temperatures come into play more when determining available energy in systems for reactions to occur, without which molecular bonds cannot be broken and things cannot dissolve or react. When you add common salt to water the reaction is endothermic as the ions take up energy to dissociate causing a drop in temperature, which is why warming the water helps dissolve salt.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637444.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637444.page GMT Chemistry help
Howard A Treesong wrote:
frgsinwntr wrote:
Howard A Treesong wrote:
frgsinwntr wrote:wait... doesn't the OH- concentration depend upon the temperature of the solution?

Or am i missing something


No, concentration is the amount per unit volume.


edited to add..

What you might be thinking of is where you put so much of a substance in that it can't all dissolve, so by heating it, you can get more to dissolve into solution. But of course the concentration is increasing because you are adding more of a solute to the solution.


Agreed, that concentration is realted to the unit pervolume, however at higher temperature the energies present allow more more OH to break off and float freely within the material correct? Its been a while since i Had PhysChem.... I'll see if I can find it later


You assume for the question that it fully dissociates and that there is no undissolved material suspended in the liquid.


awww.... but that makes it easy]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637476.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637476.page GMT Chemistry help AP)
without applying physics chem is easy.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637489.page http://www.dakkadakka.com/dakkaforum/posts/preList/414397/3637489.page GMT