Chemical tests

Describe a test for hydrogen gas

1. sample of hydrogen gas in test tube.

2. place lit splint into mouth of test tube

3. squeaky pop (hydrogen burns with oxygen in the air)

Describe a test for oxygen gas

1. collect a sample of oxygen in test tube.

2. relights a glowing splint.

Describe the test for carbon dioxide gas

1. bubble carbon dioxide gas through limewater.

2. limewater turns cloudy/milky. (calcium carbonate is formed)

Describe a test for ammonia gas

1. put damp red litmus paper in test tube containing ammonia gas.

2. turns damp red litmus paper blue.

Describe a test for chlorine gas

1. put damp blue litmus paper in test tube containing chlorine gas.

2. turns damp blue litmus paper red → bleached

Cation

positive ion

Anion

negative ion

Describe how to carry out a flame test

1. dip nichrome wire in hydrochloric acid.

2. heat wire in a roaring Bunsen flame until wire gives no colour to flame.

3. the wire is now clean.

4. dip wire into hydrochloric acid.

5. dip in substance to be tested.

6. heat wire in a safety flame.

7. observe colour change.

Lithium (Li+)

red

Sodium (Na+)

yellow

Potassium (K+)

lilac

Calcium (Ca2+)

orange-red

Copper (Cu2+)

blue-green

Describe a test for ammonium NH4+ and identify the gas evolved

1. add ammonium to sodium hydroxide solution.

2. warm the mixture.

3. ammonia gas produced.

4. turns damp red litmus paper blue.

Describe a test for Copper (Cu2+) using sodium hydroxide solution

1. add copper to sodium hydroxide solution.

2. green precipitate forms.

Fe2+ + 2OH- → Fe(OH)2

Describe a test for Iron (Fe2+) using sodium hydroxide solution

1. add iron to sodium hydroxide solution.

2. brown precipitate forms.

Fe3+ +3OH → Fe(OH)3

Describe a test for Iron (Fe3+) using sodium hydroxide solution

1. add iron to sodium hydroxide solution.

2. blue precipitate forms.

Cu2+ + 2OH- → Cu(OH)2

Describe a test for chloride, using silver nitrate solution

1. add dilute nitric acid to a solution of chloride ions.

2. add silver nitrate solution .

3. white precipitate of silver chloride formed.

Ag+(aq) + Cl-(aq) → AgCl(s)

Describe a test for Bromide using silver nitrate solution

1. add dilute nitric acid to a solution of Bromide ions.

2. add silver nitrate solution.

3. cream precipitate of silver bromide formed.

Ag+(aq) + Br-(aq) → AgBr(s)

Describe a test for iodide using silver nitrate solution

1. add dilute nitric acid to a solution of Iodide ions.

2. add silver nitrate solution.

3. yellow precipitate of silver iodide forms.

Ag(aq) + I-(aq) → AgI(s)

why is dilute nitric acid used before carrying out a chemical test?

• removes any carbonate ions that might produce a precipitate.

• this would give a false-positive result.

Describe a test for Sulfate ions (SO42-) using acidified barium chloride solution.

1. Add dilute hydrochloric acid to a solution of the sulfate ions.

2. add barium chloride solution.

3. thick, white precipitate of barium sulfate forms.

Ba2+(aq) + SO42-(aq) → BaSO4(s)

Describe a test for carbonate ions (CO32-) using hydrochloric acid and identify the gas evolved

1. add dilute hydrochloric acid to substance being testing.

2. if carbonate ions are present, there will be a reaction.

3. compound produces bubbles of carbon dioxide gas.

4. carry out test for carbon dioxide gas.

describe a test for the presence of water using anhydrous copper (II) sulfate.

when copper (II) sulfate is bound to water blue crystals are formed. (water of crystallisation)

1. heat blue hydrated copper sulfate crystals and evaporate water.

2. this leaves anhydrous copper sulfate powder (no water bound to it.)

3. add a few drops of water to white powder.

4. blue crystals form again.

describe a physical test to show whether a sample of water is pure

• boils at 100 degrees Celsius

• freezes at 0 degrees Celsius

word equation: test for water using anhydrous copper sulfate

anhydrous copper (II) sulfate + water → ← hydrated copper sulfate