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Topic: will a precipitate form?  (Read 10112 times)

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Offline Kaleyrvt

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will a precipitate form?
« on: January 16, 2007, 12:21:53 AM »
The solubility product of calcium hydroxide, Ca(OH)2, is 7.9 x 10-6 at 25ÂșC. Will a precipitate form when 100mL of 0.10 mol/L of CaCl2 solution and 50.0 mL of 0.70 mol/L of NaOH solution are combined? Show your work.

This is my work, but I dont know if I am even close-can someone check it to ensure I did it right?

[CaCl2] = 0.10 mol/L x 100 ml(0.1 L)   =  0.066 mol/L
                               150 mL(0.15 L)

[NaOH] = 0.70 mol/L x 50 ml(0.05 L)    =  0.233 mol/L
       150 mL(0.15 L)

Ksp = [CaCl2] [NaOH] = 0.015 => 1.5 x 10 -2

Since Ca(OH)2 = 7.9 x 10-6   which is < 1.5 x 10 -2 then no precipitate will form.

Thanks all ! hope to hear form you soon!

Offline AWK

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Re: will a precipitate form?
« Reply #1 on: January 16, 2007, 02:32:49 AM »
Ksp = [Ca2+] [OH-]2 = ?

A final answer is correct, but your calculations are wrong

syntax corrected
« Last Edit: January 16, 2007, 04:13:38 AM by AWK »
AWK

Offline Borek

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Re: will a precipitate form?
« Reply #2 on: January 16, 2007, 03:58:24 AM »
Ksp = [Ca2+][OH-]2
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #3 on: January 16, 2007, 11:01:12 AM »
so then where did I go wrong??All of it??? How do I find values for [Ca2+][OH-]2 ???
Sorry, just don't quite understand where to fix it...:(

Offline Borek

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Re: will a precipitate form?
« Reply #4 on: January 16, 2007, 12:17:21 PM »
You mix dissociated salt with dissociated base - you have to calculate concentrations of ions and put them into Ksp formula.
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #5 on: January 16, 2007, 01:19:52 PM »
I am sorry i am completely lost--god I feel like an idiot..:(

Offline Borek

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Re: will a precipitate form?
« Reply #6 on: January 16, 2007, 01:25:23 PM »
You have 0.233M solution of NaOH - what ions and in what concentrations does it contain?
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #7 on: January 16, 2007, 01:56:31 PM »
The NaOH contains [Na+] and [OH-] ions...how do I figure out the concentrations?
I really am trying----I am even looking through my notes :(

Offline Borek

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Re: will a precipitate form?
« Reply #8 on: January 16, 2007, 02:07:43 PM »
If there is 1 mole of NaOH dissolved - how many moles of Na+ appeared in the solution?

Note: [Na+] usually means concentration of Na+, you don't need square brackets around ions when you refer to them.
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #9 on: January 16, 2007, 02:17:14 PM »
0.5 moles of Na+?

Offline Borek

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Re: will a precipitate form?
« Reply #10 on: January 16, 2007, 02:24:04 PM »
How many Na atoms per NaOH molecule?
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #11 on: January 16, 2007, 02:28:40 PM »
1 Na atom in NaOH

Offline Borek

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Re: will a precipitate form?
« Reply #12 on: January 16, 2007, 03:36:19 PM »
So how 1 mole of NaOH could produce 0.5 mole of Na+?
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Offline Kaleyrvt

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Re: will a precipitate form?
« Reply #13 on: January 16, 2007, 04:44:35 PM »
divide 0.233M by 2= # of moles of Na+???

Offline Dan

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Re: will a precipitate form?
« Reply #14 on: January 16, 2007, 05:25:37 PM »
Think about this:

If every apple has one stalk, how many stalks do a dozen apples have?

Similarly if one NaOH unit has one Na, how many Na+ ions will 1 mol of NaOH units form?
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