Experiment 4
Gravimetric Analysis of a
Chloride Salt
Aim
• To illustrate typical techniques used in
Gravimetric Analysis by quantitatively
determining the amount of chloride in an
unknown
• Introduction:
• Two common methods used in analytical
chemistry
-a gravimetric analysis,
-volumetric analysis.
Gravimetric analysis derives its name from the
fact that the constituent being determined
can be isolated in some weighable form.
Volumetric analysis derives its name from the
fact that the method used to determine the
amount of a constituent involves measuring
the volume of a reagent.
• Chloride ion may be quantitatively
precipitated from solution by the addition of
silver ion according to the following ionic
equation:
Ag+(aq) + Cl−(aq) → AgCl(s)
• The addition of a silver nitrate solution to an
aqueous solution containing chloride ion
precipitates AgCl quantitatively
• The precipitate can be collected on a filter
paper, dried, and weighed.
• From the mass of the AgCl obtained, the
amount of chloride in the original sample can
then be calculated.
Procedure:
1. Obtain an unknown and record its number on
your report sheet.
2. On a weighing dish, weigh to the nearest 0.0001 g
about 0.2 of your unknown sample.
3. Transfer the sample quantitatively to a clean
150-mLbeaker (do not weigh the beaker) and
label the beaker #1 with pencil. Record the
sample weight.
4. Add 100 ml of distilled water and 1 ml of 6 M HNO3
to the beaker.
5. Using a glass rod, stir the solution until all of the sample has
dissolved. Leave the stirring rod in the beaker. Do not place it
on the desktop.
6.While stirring the solution, add to it about 10 ml of
0.5 M AgNO3 solution. Place a watch glass over the
beaker. White ppt will be formed
7.Obtain a filter paper and weigh it accurately. Fold it and
place it in the funnel so that one side has three folds and the
other side has one fold of paper against the funnel.
8.Wet the paper with distilled water to hold in place inside
the funnel. Transfer all the precipitate and solution from the
beaker onto the filter paper using a rubber policeman and a
wash bottle to wash out the last traces of precipitate.
9. Wash the precipitate on the filter paper with two or three
5-mL portions of distilled water from the wash bottle.
10.Finally, wash with 5-mL of acetone.
11.Repeat the above steps with the other two
samples.
12 place the sample in the oven (ask your
instructor ).