2 h) Chemical Tests

Question 1

Anhydrous

Answer 1

Without water

Question 2

Anion

Answer 2

Negative ion

Question 3

Cation

Answer 3

Positive ion

Question 4

Ion

Answer 4

Charged particle formed when an atom (or group of atoms) loses or gains electrons.

Question 5

Melting point

Answer 5

Temperature at which a substance changes state from a solid to a liquid. Pure substances have fixed melting points but a mixture may melt over a range of temperatures.

Question 6

Precipitate

Answer 6

Solid that is formed by a reaction involving liquids or gases.

Question 7

Test for halides and results

Answer 7

Add dilute nitric acid, add silver nitrate solution.
Chlorides = white precipitate
Bromide = cream precipitate
Iodide = yellow precipitate

Question 8

Flame test method

Answer 8

Dip wire loop into conc. hydrochloric acid, burn in flame until no colour is seen, dip into conc. hydrochloric acid and then into solid sample or dip into solution of sample.

Question 9

Flame colour for lithium ions

Answer 9

red

Question 10

Flame colour for sodium ions

Answer 10

yellow

Question 11

Flame colour for potassium ions

Answer 11

lilac

Question 12

Flame colour for calcium ions

Answer 12

orange-red (brick red)

Question 13

Flame colour for copper ions

Answer 13

blue-green

Question 14

Test for ammonium ion and result

Answer 14

Add sodium hydroxide solution, warm gently. Damp red litmus paper turns blue. Pungent smell.

Question 15

Test for cations using sodium hydroxide and results

Answer 15

Add sodium hydroxide solution.
copper(II) ions = blue precipitate
iron(II) ions = dirty green precipitate
iron(III) ions = orange/brown precipitate

Question 16

Test for sulphate ion and result

Answer 16

Add dilute hydrochloric acid, add barium chloride solution.

White precipitate forms.

Question 17

Test for carbonate ion and result

Answer 17

Add dilute hydrochloric acid, bubble gas produced through limewater.
Limewater turns cloudy.

Question 18

Test for oxygen gas

Answer 18

Glowing splint re-lights

Question 19

Test for hydrogen gas

Answer 19

Use a lit splint. Burns with a squeaky pop.

Question 20

Test for carbon dioxide gas

Answer 20

Bubble through limewater. Limewater turns cloudy.

Question 21

Test for ammonia gas

Answer 21

Damp red litmus paper turns blue. Pungent smell. (alternative: add hydrogen chloride gas and a white precipitate forms)

Question 22

Test for chlorine gas

Answer 22

Damp litmus paper is bleached. (chlorine is a green gas)

Question 23

Test for the presence of water

Answer 23

Anhydrous copper(II) sulphate turns from white to blue.

Question 24

Test for the purity of water

Answer 24

Boils at 100 degrees C

Melts at 0 degrees C