SUMMARY OF QUALITATIVE TESTS - The Laboratory - REVIEW OF MAJOR TOPICS - SAT Subject Test Chemistry

SAT Subject Test Chemistry

PART 2

REVIEW OF MAJOR TOPICS

CHAPTER 15

The Laboratory

SUMMARY OF QUALITATIVE TESTS

I. Identification of Some Common Gases

Gas

Test

Result

Ammonia

1. Smell cautiously.

1. Sharp odor.

NH3

2. Test with litmus.

2. Red litmus turns blue.

3. Expose to HCl fumes.

3. White fumes form, NH4Cl.

Carbon dioxide

1. Pass through limewater,

1. White precipitate forms,

CO2

Ca(OH)2

CaCO3

Carbon monoxide
CO

1. Burn it and pass product through limewater, Ca(OH)2

1. White precipitate forms, CaCO3

Hydrogen
H2

1. Allow it to mix with some air, then ignite.

1. Gas explodes.

2. Burn it—trap product.

2. Burns with blue flame—product H2O turns cobalt chloride paper from blue to pink.

Hydrogen chloride

1. Smell cautiously.

1. Choking odor.

HCl

2. Exhale over the gas.

2. Vapor fumes form.

3. Dissolve in water and test with litmus.

3. Blue litmus turns red.

4. Add AgNO3 to the solution.

4. White precipitate forms.

Hydrogen sulfide

1. Smell cautiously.

1. Rotten egg odor.

H2S

2. Test with moist lead acetate paper.

2. Turns brown-black (PbS).

Oxygen

1. Insert glowing splint.

1. Bursts into flame.

O2

2. Add nitric oxide gas.

2. Turns reddish brown.

II. Identification of Some Negative Ions

Ion

Test

Result

Acetate

Add concentrated H2SO4 and warm

Odor of vinegar released.

C2H3O2−

gently.

Carbonate
CO3−

Add HCl acid; pass released gas through limewater.

White, cloudy precipitate forms.

Chloride

1. Add silver nitrate solution.

1. White precipitate forms.

Cl−

2. Then add nitric acid, later followed by ammonium hydroxide.

2. Precipitate insoluble in HNO3 but dissolves in NH4OH.

Hydroxide

Test with red litmus paper.

Turns blue.

OH−

Sulfate

Add solution of BaCl2, then HCl.

White precipitate forms; insoluble in HCl.

SO4−

Sulfide
S2−

Add HCl and test gas released with lead acetate paper.

Gas, with rotten egg odor, turns paper brown-black.

III. Identification of Some Positive Ions

Ion

Test

Result

Ammonium

Add strong base (NaOH);

Odor of ammonia.

NH4+

heat gently.

Ferrous
Fe2+

Add solution of potassium ferricyanide,
K3Fe(CN)6

Dark blue precipitate forms
(Turnball”s blue).

Ferric
Fe3+

Add solution of potassium ferrocyanide,
K4Fe(CN)6.

Dark blue precipitate forms
(Prussian blue).

Hydrogen

Test with blue litmus paper.

Turns red.

H+

IV. Qualitative Tests of Some Metals

FLAME TESTS. Carefully clean a platinum wire by dipping it into dilute HNO3 and heating in the Bunsen flame. Repeat until the flame is colorless. Dip heated wire into the substance being tested (either solid or solution), and then hold it in the hot outer part of the Bunsen flame.

Compound of

Color of Flame

Sodium (Na)

Yellow

Potassium (K)

Violet (use cobalt-blue glass to screen out Na impurities)

Lithium (Li)

Crimson

Calcium (Ca)

Orange-red

Barium (Ba)

Green

Strontium (Sr)

Bright red

HYDROGEN SULFIDE TESTS. Bubble hydrogen sulfide gas through the solution of a salt of the metal being tested. Check color of the precipitate formed.

Compound of

Color of Sulfide Precipitate

Lead (Pb)

Brown-black (PbS)

Copper (Cu)

Black (CuS)

Silver (Ag)

Black (Ag2S)

Mercury (Hg)

Black (HgS)

Nickel (Ni)

Black (NiS)

Iron (Fe)

Black (FeS)

Cadmium (Cd)

Yellow (CdS)

Arsenic (As)

Light yellow (As2S3)

Antimony (Sb)

Orange (Sb2S3)

Zinc (Zn)

White (ZnS)

Bismuth (Bi)

Brown (Bi2S3)