During the second week, suppose you decide to use volumetric analysis. For each
ID: 483427 • Letter: D
Question
During the second week, suppose you decide to use volumetric analysis. For each of the unknown compounds on the left, choose the proper titrant (standard solution) and indicator from the drop-down box. There are three indicators for you to choose from: bromothymol blue, phenolphthalein, and methyl orange.
Hints:
HCl is a strong acid;
NaOH is a strong base;
CH3COONa, Na2C2O4 are basic salts that form weak bases in aqueous solutions;
NH4Cl is an acidic salt that forms weak acid in an aqueous solution.
CH3COONa
[ Choose ] HCl, methyl orange NaOH, phenolphthalein HCl, phenolphthalein, and then methyl orange HCl, bromothymol blue
Na2CO3
[ Choose ] HCl, methyl orange NaOH, phenolphthalein HCl, phenolphthalein, and then methyl orange HCl, bromothymol blue
Na2C2O4
[ Choose ] HCl, methyl orange NaOH, phenolphthalein HCl, phenolphthalein, and then methyl orange HCl, bromothymol blue
NH4Cl
[ Choose ] HCl, methyl orange NaOH, phenolphthalein HCl, phenolphthalein, and then methyl orange HCl, bromothymol blue
NaOH
[ Choose ] HCl, methyl orange NaOH, phenolphthalein HCl, phenolphthalein, and then methyl orange HCl, bromothymol blue
Explanation / Answer
We need to find the approx. equivalent pH so we can choose an indicator...
CH3COONa +strong acid HCl - methyl orange (pH will be about 4.5)
Na2CO3 base ---> strong acid HCl- phenolphthalein (pH will be 7-8) , and then methyl orange (since carbonic acid has 2 equivalence points, it needs two indicators)
Na2C2O4 HCl- methyl orange, and then methyl orange (since oxalic acid has 2 equivalence points, it needs two indicators)
NH4Cl NaOH- Phenolphthalein, since pH = 9.75 approx
NaOH HCl-Bromothymol blue --> since pH = 7 best for a neutral indicator
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