Illustrated Guide to Home Chemistry Experiments

350 DIY Science: Illustrated Guide to Home Chemistry Experiments

CUTIOA nS

Hydrochloric acid, nitric acid, and sodium hydroxide are

corrosive. Some of the salts used in this lab session are

poisons, oxidizers, corrosives, or otherwise hazardous.

Read the MSDS for each chemical before you use it. Wear

splash goggles, gloves, and protective clothing.

z

This laboratory has two parts. In Part I, we’ll prepare the bone
sample for analysis. In Part II, we’ll determine whether eight
specific ions are present in the sample: chloride, sulfate, phosphate,
calcium, iron(III), sodium, ammonium, and potassium.

POCEDURER

PART I: SAppEm L REpARATIoN
In Part I, we prepare the bone sample for analysis by digesting
it in dilute nitric acid. This procedure should be done outdoors,
under an exhaust hood, or in an otherwise well-ventilated area.
The reaction of nitric acid with the bone sample evolves toxic
and irritating fumes of nitrogen oxides. Do not breathe these
fumes or allow them to contact your eyes or skin.

1. If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.


2. Weigh a 1.0 g sample of bone. If possible, use small
   pieces rather than one large chunk.


3. Add 25 mL of 6 M nitric acid to 25 mL of distilled or
   deionized water in a 150 mL beaker. Place the
   beaker on a support ring and wire gauze over the
   gas burner.


4. Add the bone sample to the beaker and heat the beaker
   gently, with stirring, to dissolve the bone sample. Do not
   boil the solution. As the bone sample dissolves, toxic
   fumes are evolved.


5. Continue heating and stirring the solution in the beaker
   for 10 or 15 minutes. As the reaction progresses, the
   quantity of fumes evolved rapidly diminishes. Some solid
   matter remains undissolved.


6. Remove the heat and allow the beaker to cool to room
   temperature.


7. Set up a funnel with filter paper and the second 150 mL
   beaker as the receiving vessel.


8. Filter the solution into the second beaker and
   discard the filter paper and solid filtrand. The filtrate
   is your sample.

PII: RTA ANALySIS of IoNS
In Part II, we analyze the sample to determine whether
chloride, sulfate, phosphate, calcium, iron(III), sodium,
ammonium, and/or potassium ions are present.

1. If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.


2. Transfer 5 mL of the sample to the first test tube.
   Add several drops of 0.1 M silver nitrate solution. A
   precipitate confirms the presence of chloride ions.
   (Actually, a precipitate confirms the presence of
   chloride, bromide, or iodide ions, but the bromide and
   iodide ions are present in extremely low concentrations
   in animal bone, so we can assume that any precipitate is
   caused by chloride ions.) Note your observations on
   line A of Table 19-6.


3. Transfer 5 mL of the sample to the second test tube.
   Add 10 drops of 0.1 M barium chloride to the test tube,
   stir or swirl to mix the solution, and look for a white
   precipitate that confirms the presence of sulfate ions.
   Record your observations on line B of Table 19-6.


4. Transfer 5 mL of the sample to the third test tube. Add
   about 4 mL of 6 M nitric acid and 6 mL of ammonium
   molybdate to the test tube and mix the solution well. A
   yellow precipitate confirms the presence of phosphate
   ion. If no precipitate occurs immediately, continue
   observing the test tube for a minute or two. If there is
   still no precipitate, heat the test tube very gently for
   a minute or two. (Do not heat the solution strongly.
   Doing so may cause a precipitate of white molybdenum
   trioxide, which is not a positive test for phosphate ions.)
   Record your observations on line C of Table 19-6.


5. Transfer about 3 mL of the sample to the fourth test
   tube. Add about 15 mL of 0.2 M ammonium oxalate and
   mix the solutions thoroughly. A white precipitate or white
   cloudiness confirms the presence of the calcium ion.
   (Under the acidic conditions of this test, calcium oxalate
   is more soluble than it is in neutral solution. Examine
   the test tube carefully; even a slight white cloudiness is
   a positive result.) Record your observations on line D of
   Table 19-6.


6. Transfer 5 mL of the sample to the fifth test tube. Add 5
   mL of 6 M nitric acid and mix thoroughly. Add 5 drops
   of 0.1 M potassium thiocyanate, mix thoroughly, and
   look for a color change. A blood red color (Figure 19-5)
   indicates the presence of Fe(III) ion in relatively high
   concentration. At lower concentrations of Fe(III) ion, the
   solution assumes anything from a light red color to a
   very pale straw yellow color. Record your observations
   on line E of Table 19-6.

FIGURE 19-5:

Ferric ions react with

potassium thiocyanate

to produce a blood red

complex