Separation and Qualitative Determination of Cations and Anions
: The purpose of this lab was to use qualitative analysis to determine
which cations and anions were present in a solution.
Qualitative Analysis of Cations
1. Separation of the Silver from Iron, Copper,
and Zinc ions.
First add 8 drops of 6 M HCl to the solution and
stir. A white Ag precipitate should form and
indicate that Ag is present. Then centrifuge the
solution. To double check that the precipitation
is complete, add one more drop of the 6 M HCl.
Next, centrifuge, pour off, and save the clear
liquid because it will be used again in step three.
Label it 1c. Last, wash the precipitate with 1 mL of distilled water,
centrifuge and discard the wash water, however the precipitate should be
saved. Label the precipitate 1d.
2. Confirmation of Silver
First, add 1 mL of 6 M NH
to the precipitate formed in part 1d of the
procedure, and stir until the precipitate completely dissolves. Now, add 15
drops of 6 M HCl to the solution. If silver is present, heat will be given off
and the test tube could get very warm. Next, stir the solution and test it with
pH indicator paper. The solution should be acidic. If it’s not, add more HCl,
and if the white precipitate forms in the solution, this means that silver is
present. Dispose of the silver compound.
3. Separation of Iron and Copper from Zinc
Add 6 M NaOH to the solution labeled 1c. Be sure to stir while the NaOH is
being added. Continue to add this until the solution becomes basic. Once it’s
basic, add three more drops. Next, stir the solution and place it in a hot
water bath for three minutes. If a precipitate forms, that means that copper,
iron or both elements may be present. Centrifuge the solution, and separate
the solid from the liquid. Save the clear solution and label it 3c. Wash the
precipitate with a mixture that contains 10 drops of 6 M NaOH and 10 drops
of water. Centrifuge this and be sure to discard the wash water. Save the
precipitate and label it 3e.
4. Separation of Iron from Copper; Confirmation of Copper
Add five drops of water to precipitate 3e and add 6 M H
the solution is acidic, and stir until the precipitate is dissolved. To the new
solution add 6 M aqueous NH
until the solution is basic. Then add 1 mL
extra. Centrifuge and separate the supernatant liquid from the precipitate and
save the precipitate, label it 4d. Dispose of the copper solution.