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 |
1. Burn it and pass product through limewater, Ca(OH)2 |
1. White precipitate forms, CaCO3 |
Hydrogen |
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 |
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 |
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 |
Add solution of potassium ferricyanide, |
Dark blue precipitate forms |
Ferric |
Add solution of potassium ferrocyanide, |
Dark blue precipitate forms |
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) |