Tests for Substances

Question 1

How do you test for lithium?

Answer 1

when heated it burns with a crimson-red flame

Question 2

How do you test for sodium?

Answer 2

when heated it burns with a yellow-orange flame

Question 3

How do you test for potassium?

Answer 3

when heated it burns with a lilac flame

Question 4

How do you test for calcium?

Answer 4

when heated it burns with a brick-red flame

Question 5

How do you test for NH₄⁺ (ammonium ions)?

Answer 5

By using sodium hydroxide and identifying the ammonia evolved.

• ammonium ions + hydroxide ions > ammonia + water
• to check whether ammonia has been produced, there will be a pungent smell, but ammonia gas will turn damp red litmus paper blue

Question 6

How do you test for copper ions?

Answer 6

By adding it to sodium hydroxide solution:

• a blue precipitate should be formed

Question 7

How do you test for Fe²⁺ ions?

Answer 7

By adding it to sodium hydroxide solution:

• a sludgy green precipitate should be formed

Question 8

How do you test for Fe³⁺ ions?

Answer 8

By adding it to sodium hydroxide solution:

• a reddish brown precipitate should be formed

Question 9

How do you test for chloride ions?

Answer 9

By using dilute nitric acid and siver nitrate solution:

• a white precipitate of silver chloride should be formed

Question 10

How do you test for bromide ions?

Answer 10

By using dilute nitric acid and siver nitrate solution:

• a cream precipitate of silver bromide should be formed

Question 11

How do you test for iodide ions?

Answer 11

By using dilute nitric acid and siver nitrate solution:

• a yellow precipitate of silver iodide should be formed

Question 12

How do you test for SO₄^2- (sulphate ions)?

Answer 12

By using hydrochloric acid and barium chloride solution:

• a white precipitate should form

Question 13

How do you test for CO₃^2- (carbonates)?

Answer 13

By using dilute hydrochloric acid and identifying the carbon dioxide formed:

• to test for carbon dioxide, lime water should turn cloudy

Question 14

How do you test for hydrogen gas?

Answer 14

Burns with a squeaky pop.

Question 15

How do you test for oxygen gas?

Answer 15

It should relight a glowing splint.

Question 16

How do you test for carbon dioxide gas?

Answer 16

When bubbled through lime water, the lime water should go cloudy.

Question 17

How do you test for ammonia gas?

Answer 17

It will turn damp red litmus paper blue.

(also a very strong smell)

Question 18

How do you test for chlorine gas?

Answer 18

It will bleach damp litmus paper.

Question 19

Why, when testing for the presence of ions in a substance, would an acid be added before a metal solution?

Answer 19

To get rid of any traces of carbonate/sulphate ions which might confuse the precipitate result.

Question 20

What would be a chemical test for checking whether something contained water?

Answer 20

Anhydrous (white) copper sulphate should turn blue.

Question 21

What is the chemical formula of nitric acid?

Answer 21

HNO₃

Question 22

What two observations can be made when magnesium burns in air?

Answer 22

• White flame is produced.
• White solid is produced (magnesium oxide).