Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: realMelody on September 17, 2023, 10:16:33 AM
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I have a question related to solubility and Ksp in a chemical reaction. I don't want to seek answers to a specific homework problem, but I'm genuinely stuck and seeking a deeper understanding of the concept. Can someone please explain the process for determining the mass of a precipitate in a given scenario when considering the solubility product constant (Ksp)? I'm not sure how to proceed, and I'm looking for guidance on the general approach.
This specifically is the question I have been having some problems with:
How many grams of precipitate would we have if
50 mL of 0.200 mol/L CH3COONa is mixed with
200 mL 0.100 mol/L AgNO3?
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to get help from someone you might show what you have done so far like
writing a balanced equation. there are buttons in the editor to help with this and latex is supported
edit
I have moved this entry to a forum board that may be more appropriate.
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I did try that but can't seem to find the right answer.
How much precipitate would be produced if the reation went to completion:
Moles of CH3COONa = Concentration x Volume = 0.200 mol/L x 0.050 L = 0.010 mol
Since the reaction is 1:1 between CH3COONa and AgCH3COO, the moles of AgCH3COO produced will also be 0.010 mol.
Calculate the mass of AgCH3COO produced:
Molar mass of AgCH3COO = 107.87 g/mol (Ag) + 12.01 g/mol (C) + 3 x 1.01 g/mol (H) + 2 x 16.00 g/mol (O) = 166.912 g/mol
Mass of AgCH3COO produced = Moles x Molar mass = 0.010 mol x 166.912 g/mol ≈ 1.669 g
Calculate the molar solubility (amount that stays dissolved) using the corrected Ksp:
Ksp for AgCH3COO is given as 1.94 x 10^-3 mol^2/L^2.
To find the molar solubility (S), we'll take the square root of Ksp.
S = √(Ksp) = √(1.94 x 10^-3 mol^2/L^2) ≈ 0.044 mol/L
Calculate the moles of AgCH3COO that will stay dissolved (molar solubility):
Moles of AgCH3COO not precipitated = Molar solubility x Volume = 0.044 mol/L x 0.250 L = 0.011 mol
Calculate the mass of AgCH3COO that will not precipitate:
Mass of AgCH3COO not precipitated = Moles x Molar mass = 0.011 mol x 166.912 g/mol ≈ 1.836 g
And then I subtracted the latter from the former as you said and 1.836 -1.669 g ≈ 0.167 g
But the correct answer is 0.484g :(
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S = √(Ksp) only applies if [Ag+] = [AcO-]. Is that the case here?
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Last Calculations are not logic and wrong.
You found 0,01 mol CH3COOAg will be formed from 250 ml.
S = 0,044 mol/l what means 0,011 mol for 250 ml.
So if 0,011 mol is still soluble how can 0,01 mol then precipitate?
We have 0,02 mol Ag+ and 0,01 mol Acetate ions to combine.
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Write the solubility product as a different with x.
Start concentration of Ag+ minus x and the same with Acetate -x.
Concentration in mol/l . Mass calculated to 250 ml.
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Are you sure that answer is 0.48 g? Maybe 1.48 g?
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No its 0,485 g
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@ ProfOxidizer
I agree with Hunter 2. 0.485g looks good to me.