Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Problem of the Week Archive => Topic started by: Borek on February 25, 2013, 08:01:07 AM
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Silver nitrate solution was added to 10 mL of sodium sulfate solution. Assuming concentrations of both solutions were high enough to produce a precipitate, at what volume of the AgNO3 added amount of solid is at its maximum?
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this Is probably wrong, but Is it 20ml?
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Please show how you got this result.
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Let [Ag] and [SO4] be the initial concentration of the 2 ions in the various solutions.
Let the amount of AgNO3 solution added be Xml
When combined, [tex][Ag]new= \frac{x[Ag]}{x+10}[/tex], [tex][SO_4]new= \frac{10[SO_4]}{x+10}[/tex]
Thus, [tex]Ksp = \frac{10x^2[Ag]^2[SO_4]}{(x+10)^3}[/tex]
[Ag]2[SO4]=1.2x10-5 (Actually specific value doesn't matter)
Sub this into the Ksp equation, then max X is when [tex]\frac{d}{dx} \frac{10x^2×1.2×10^{-5} }{(x+10)^3}=0[/tex]
Solving, X=20.
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Perfect!
Funny how the result doesn't depend on the initial concentrations nor the Ksp. Also, while the differential looks rather unpleasant, finding the maximum is quite simple - it is enough to compare the numerator to zero and it is just x(x-20)=0.
I am correcting a typo in your LaTeX - 10^(-5) is not equivalent to 10^{-5}.
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I am correcting a typo in your LaTeX - 10^(-5) is not equivalent to 10^{-5}.
Thanks! Was actually trying to figure out why the ^-5 couldn't be displayed correctly, but couldn't find the problem.
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In LaTeX {} are used for grouping of symbols, () are treated like every other character.