Chapter 19 Laboratory: Qualitative Analysis 345CUTIOA nS
Hydrochloric, nitric, and sulfuric acids and concentrated
aqueous ammonia are corrosive. Some of the metal salts
used in this lab session are poisons, oxidizers, corrosives,
or otherwise hazardous. Some are known or suspected
carcinogens. Read the MSDS for each chemical before
you use it. Wear splash goggles, gloves, and protective
clothing. Wear a disposable N100 respirator mask if you
handle any of the hazardous chemicals in solid form.
Dispose of all chemical wastes properly, in accordance
with hazardous material disposal laws and regulations.z
turns blue) and then add the same volume of ammonia
again to make the ammonia in large excess. Determine
whether the precipitate dissolves in excess ammonia.
Note your observations in Table 19-5.- Add a few drops of 6 M hydrochloric acid to the
second test tube and swirl or stir the tube gently. If no
observable change occurs, note that fact in Table 19-5
and continue to the next step. If adding hydrochloric
acid produces a visible change such as a precipitate,
color change, bubbling, or some other action, continue
adding hydrochloric acid until no further change occurs.
If a precipitate occurs, continue adding hydrochloric
acid with stirring until you have added twice the amount
of acid required to reach the first endpoint and see if
the precipitate redissolves. If the precipitate does not
redissolve, neutralize the hydrochloric acid to litmus
paper with aqueous ammonia and continue until the
ammonia is in large excess to determine whether the
precipitate dissolves in excess ammonia. Note your
observations in Table 19-5. - Add a few drops of 6 M sodium hydroxide to the
third test tube and swirl or stir the tube gently. If no
observable change occurs, note that fact in Table
19-5 and continue to the next step. If adding sodium
hydroxide produces a visible change such as a
precipitate, color change, bubbling, or some other
action, continue adding sodium hydroxide until no
further change occurs. If a precipitate occurs, continue
adding sodium hydroxide with stirring until you have
added twice the amount of sodium hydroxide required to
reach the first endpoint and see whether the precipitate
redissolves. If the precipitate does not redissolve with
excess sodium hydroxide, test it with excess aqueous
ammonia and then with excess nitric acid. Note your
observations in Table 19-5. - Add a few drops of 6 M aqueous ammonia to the fourth
test tube and swirl or stir the tube gently. If no observable
change occurs, note that fact in Table 19-5 and continue
to the next step. If adding ammonia produces a visible
change such as a precipitate, color change, bubbling, or
some other action, continue adding ammonia until no
further change occurs. If a precipitate occurs, continue
adding ammonia with stirring until you have added
twice the amount of ammonia required to reach the first
endpoint and see whether the precipitate redissolves.
If the precipitate does not redissolve with excess
ammonia, test it with excess nitric acid. Note your
observations in Table 19-5.- Add a few drops of 0.25 M potassium ferricyanide to
the fifth test tube and swirl or stir the tube gently. If no
observable change occurs, note that fact in Table 19-5
and continue to the next step. If adding potassium
ferricyanide produces a visible change such as a
precipitate or color change, continue adding potassium
ferricyanide until no further change occurs. If no visible
change occurs, add one or two drops of nitric acid to
the test tube and note any visible change. If acidifying
the solution causes no change, add three or four drops
of sodium hydroxide and note any visible changes. Note
your observations in Table 19-5. See Figure 19-4. - Add a few drops of 0.25 M potassium ferrocyanide to
the sixth test tube and swirl or stir the tube gently. If no
observable change occurs, note that fact in Table 19-5
and continue to the next step. If adding potassium
ferrocyanide produces a visible change such as a
precipitate or color change, continue adding potassium
ferrocyanide until no further change occurs. If no visible
change occurs, add one or two drops of nitric acid to
the test tube and note any visible change. If acidifying
the solution causes no change, add three or four drops
of sodium hydroxide and note any visible changes. Note
your observations in Table 19-5. - Add a few drops of 0.25 M potassium thiocyanate to the
seventh test tube and swirl or stir the tube gently. If no
observable change occurs, note that fact in Table 19-5
and continue to the next step. If adding potassium
thiocyanate produces a visible change such as a
precipitate or color change, continue adding potassium
thiocyanate until no further change occurs. If no visible
change occurs, add one or two drops of nitric acid to
the test tube and note any visible change. If acidifying
the solution causes no change, add three or four drops
of sodium hydroxide and note any visible changes. Note
your observations in Table 19-5.
Discard all solutions and precipitates in the hazardous
waste container, and wash all of the test tubes
thoroughly.
Repeat steps 1 through 10 for each of the other cation
sample solutions.