2g-Chemical tests

Question 1

Question: How do you test for hydrogen gas?

Answer 1

Answer: Collect the gas in a test tube and apply a lit splint. Hydrogen burns with a squeaky pop.

Question 2

Question: How do you test for oxygen gas?

Answer 2

Answer: Insert a glowing splint into the gas. Oxygen relights the splint.

Question 3

Question: How do you test for carbon dioxide gas?

Answer 3

Answer: Bubble the gas through limewater. Carbon dioxide turns limewater milky.

Question 4

Question: How do you test for chlorine gas?

Answer 4

Answer: Hold damp blue litmus paper in the gas. Chlorine bleaches the paper white.

Question 5

How do you test for ammonia gas?

Answer 5

Answer: Hold damp red litmus paper in the gas. Ammonia turns the paper blue.

Question 6

Question: How do you test for water?

Answer 6

Answer: Use anhydrous copper(II) sulfate. It changes from white to blue in the presence of water.

Question 7

Question: How do you test for cations using a flame test?Answer:

Answer 7

Lithium (Li⁺): Red flame

Sodium (Na⁺): Yellow flame

Potassium (K⁺): Lilac flame

Calcium (Ca²⁺): Orange-red flame

Copper (Cu²⁺): Green flame

Question 8

Question: How do you test for cations using sodium hydroxide solution?Answer:

Answer 8

Copper (Cu²⁺): Blue precipitate

Iron (II) (Fe²⁺): Green precipitate

Iron (III) (Fe³⁺): Brown precipitate

Ammonium (NH₄⁺): Produces ammonia gas when heated

Question 9

Question: How do you test for anions?Answer:

Answer 9

Chloride (Cl⁻): White precipitate with silver nitrate

Bromide (Br⁻): Cream precipitate with silver nitrate

Iodide (I⁻): Yellow precipitate with silver nitrate

Sulfate (SO₄²⁻): White precipitate with barium chloride

Carbonate (CO₃²⁻): Produces carbon dioxide when reacted with acid

Question 10

Question: How do you test for the presence of water?

Answer 10

Answer: Heat copper(II) sulfate crystals. If water is present, blue hydrated crystals turn white when dehydrated.

Question 11

Practical: Testing for Ions

Method:

Answer 11

Perform flame tests using a clean nichrome wire loop.

Add sodium hydroxide solution to metal ion solutions and observe precipitates.

Question 12

Practical: Testing for Ions
Results & conclution

Answer 12

Different flame colors and precipitate colors indicate specific ions.

Conclusion:

These tests identify metal cations and anions in unknown compounds.