inorganic chemistry - chemical tests

Question 1

test for hydrogen

Answer 1

hold a lit splint to the mouth of a test tube containing gas. if a squeaky pop sound is heard, the gas is hydrogen

Question 2

test for carbon dioxide

Answer 2

bubble the gas through limewater. if the gas is CO2, the limewater will go cloudy.

Question 3

test for oxygen

Answer 3

use a glowing splint and hold it to the mouth of a test tube containing gas. if the gas is oxygen, the splint will reignite.

Question 4

test for ammonia

Answer 4

dip damp red litmus in the liquid. if the liquid contains ammonia, it will turn blue

Question 5

test for chlorine

Answer 5

dip damp blue litmus paper in the liquid. if the liquid contains ammonia, it will turn white as it has been bleached.

Question 6

how to carry out flame test

Answer 6

a flame test is used to show the presence of certain cations in a compound.

• A platinum wire is dipped into concentrated hydrochloric acid to remove any impurities.
• platinum is used as it has a high melting point.
• The wire is dipped into the salt being tested so some salt sticks to the end.
• The wire and salt are held in a (roaring) bunsen burner flame.
• The colour is observed.

Question 7

what colour does lithium turn

Answer 7

red

Question 8

what colour does sodium turn

Answer 8

yellow

Question 9

what colour does potassium turn

Answer 9

lilac

Question 10

what colour does calcium turn

Answer 10

orange-red

Question 11

what colour does copper turn

Answer 11

blue-green

Question 12

test for NH4+, ammonium ions using sodium hydroxide

Answer 12

• add sodium hydroxide and warm
• if ammonium ions are present, ammonia gas will form
• this turns the damp red litmus paper blue

Question 13

test for Cu2+, copper (III) ions using sodium hydroxide

Answer 13

• add sodium hydroxide
• if Cu2+ is present, a blue precipitate of copper hydroxide will form

Question 14

test for Fe2+, iron (II) ions using sodium hydroxide

Answer 14

• add sodium hydroxide
• if Fe2+ is present, a green precipitate of iron (II) hydroxide will form

Question 15

test for Fe3+, iron (III) ions using sodium hydroxide

Answer 15

• add sodium hydroxide
• if Fe3+ is present, a brown precipitate of iron (III) hydroxide will form

Question 16

test for CO3 2- using hydrochloric acid

Answer 16

• add hydrochloric acid
• if carbonate ions are present, fizzing will occur

Question 17

test for Cl-, Br- and I- using acidified silver nitrate

Answer 17

• add nitric acid to remove impurities
• add silver nitrate solution
• if chloride ions are present, a white precipitate of silver chloride will form
• if bromide ions are present, a cream precipitate of silver bromide will form
• if iodide ions is present, a yellow precipitate of silver iodide will form

Question 18

test for SO4 2- using acidified barium chloride solution

Answer 18

• add hydrochloric acid to remove impurities
• add barium chloride solution
• if sulphate ions are present, a white precipitate of barium sulphate will form

Question 19

test for CO3 2- using hydrochloric acid

Answer 19

• add hydrochloric acid
• if carbonate ions are present, fizzing will occur

Question 20

test for the presence of water using anhydrous copper (II) sulphate

Answer 20

• add anhydrous copper (II) sulphate to sample
• if water is present, the sulphate will turn from white to blue

Question 21

physical test to see if water is pure

Answer 21

test the boiling or melting point. pure water boils at 100 degrees and melts at 0 degrees.