Illustrated Guide to Home Chemistry Experiments

336 DIY Science: Illustrated Guide to Home Chemistry Experiments

SBSTITUTIU oNS ANd modIfICATIoNS

• You may substitute hydrated sodium carbonate (or washing soda) for the borax, although the colors will be different.


• Salts of gold and tungsten are difficult to obtain, but try to obtain samples of salts of each of the other metals listed in Table
  19-3. The metal can be present as a cation (for example, cobalt carbonate for cobalt or copper sulfate for copper) or as an
  anion (for example, potassium permanganate for manganese or sodium dichromate for chromium).

LABORATORY 19 .2:

USE BoRAx BEAd TESTS To dISCRImINATE mETAL IoNS

The borax bead test is a fast, sensitive test

for the presence of chromium, copper, cobalt,

gold, iron, manganese, nickel, and tungsten.

The borax bead test works because very low

concentrations of the oxides of these metals

in their oxidized and reduced states impart

characteristic colors to a transparent borax

bead. (Table 19-3 lists the characteristic

colors.) Although it is seldom used nowadays

for serious qualitative analysis work, the borax

bead test was formerly used frequently by

geologists and others for field tests of ore-

bearing rock. It requires little equipment, and is

sufficiently sensitive to use as a screening test.

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ gas burner

£ inoculating loop (platinum or Nichrome)

£ borax (~1 g)

£ samples (see Substitutions and modifications)

TABLE 19-3: Borax bead colors by element, flame type, and bead temperature

Element

Reducing flame

(hot bead)

Reducing flame

(cold bead)

Oxidizing flame

(hot bead)

Oxidizing flame

(cold bead)

Chromium Green Green Yellow to yellow-green Green

Cobalt Blue Blue Blue Blue

Copper Colorless Red to reddish brownGreen to light blue-green Blue

Gold Red Violet Rose to violet Rose to violet

Iron Pale green to green Green Brown to yellow Yellow

Manganese Colorless Colorless Violet Violet

Nickel Gray Gray Violet to brown Reddish brown

Tungsten Green Blue Pale yellow Colorless