C4.2 Identifying Products Of Chemical Reactions

Question 1

How you can detect carbon dioxide

Answer 1

Test using limewater, mixture of calcium hydroxide solution
Bubbling carbon dioxide through limewater
Goes cloudy white

Question 2

How you can detect chlorine

Answer 2

Damp blue litmus paper
Paper turns red then white
(Also never say “chlorine ions”, chlorine is an element, “chloride ions”.)

Anion test:
Add few drops of silver nitrate solution and white precipitate should form

Question 3

How you can detect hydrogen

Answer 3

Lit splint in test tube
Squeaky pop

Question 4

How you can detect oxygen

Answer 4

Glowing splint relights when put near mouth of the test tube

Question 5

Flame test

Answer 5

When metal ions are heated energy is transferred to their electrons
This makes them move to higher electron shells
When they move back to their normal electron shells energy is transferred to the surroundings as radiation seen as light
Different metal ions produce different colours of light

Question 6

Tests for Lithium

Answer 6

Ion: Li+

Flame: Red or crimson
Sodium hydroxide test: N/A

Question 7

Tests for Sodium

Answer 7

Ion: Na+

Flame: yellow
Sodium hydroxide test: N/A

Question 8

Tests for Potassium

Answer 8

Ion: K+

Flame: lilac
Sodium hydroxide test: N/A

Question 9

Tests for Calcium

Answer 9

Ion: Ca2+

Flame: orange-red
Sodium hydroxide test: White precipitate

Question 10

Tests for Copper(II)

Answer 10

Ion: Cu2+

Flame: green-blue
Sodium hydroxide test: Blue precipitate

Question 11

Prepare flame test

Answer 11

Clean nichrome wire loop before test by dipping in hydrochloric acid
Rinse with distilled water
Dip clean loop in test powder or solution
Hold above a roaring flame
Clean for each test

Question 12

What are hydroxide precipitate tests

Answer 12

Group 1 hydroxides are soluble in water but most other metal hydroxides are insoluble
Different metals produce different coloured precipitates
Add a few drops of sodium hydroxide solution to a solution containing metal ions

Question 13

Tests for iron(ll)

Answer 13

Ion: Fe2+
Flame test: N/A
Sodium hydroxide test: green precipitate

Question 14

Tests for iron(lll)

Answer 14

Ion: Fe3+

Flame test: N/A
Sodium hydroxide test: orange-brown precipitate

Question 15

Tests for zinc

Answer 15

Ion: Zn2+

Flame test: N/A
Sodium hydroxide test: white precipitate

Question 16

What happens when excess sodium hydroxide is added to zinc hydroxide

Answer 16

Zinc hydroxide dissolves to form a colourless solution

Question 17

Anion test for sulphate ions

Answer 17

Add dilute HYDROCHLORIC ACID to remove any carbonate ions
Then add few drops of BARIUM CHLORIDE solution (BaCl2(aq))
White precipitate if sulfate ions are present

Example: BaCl2(aq) + K2SO4(aq) -> 2KCl(aq) + BaSO4
Ionic equation: Ba 2+(aq) + SO4 2-(aq) -> BaSO4(s)

Question 18

Anion test for carbonate ions

Answer 18

Add metal carbonate to dilute acid
Bubbles of carbon dioxide gas will be produced
Check by bubbling the carbon dioxide through limewater
Metal carbonate + acid -> salt + water + carbon dioxide

Example: MgCO3(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l) + CO2(g)
Ionic equation: CO3 2- + 2H + -> CO2 + H2O

Question 19

Anion test for halide ions

Answer 19

Add a few drops of nitric acid
Add few drops of silver nitrate solution (AgNO3(aq))

If chlorine: Cl: white precipitate
If bromine: Br: cream precipitate
If iodine: I: yellow precipitate

Example: NaCl(aq) + AgNO3(aq) -> NaNO3(aq) + AgCl(s)
Ionic equation: Ag +(aq) + X -(aq) -> AgX(s)

Question 20

Instrumental methods of analysis

Answer 20

Relies on a machine to carry out an analysis of a substance
Can analyse very small amounts of substances if difficult to obtain, very sensitive
Very accurate results, calibrated using international standards
Instruments can carry out analyses quickly and they can run all the time

Question 21

How do you interpret gas chromatograms

Answer 21

Each peak represents a substance present in the mixture
Areas under each peak show the relative amount of each substance in the mixture
Retention time for a substance to travel through the chromatography column is different for different substances

Question 22

How do you interpret mass spectra

Answer 22

Can measure masses of atoms and molecules
Used to analyse relative amounts of different isotopes of an element and structure of molecules
Used to detect toxic substances
Harmful as it ionises the sample and breaks it down into fragments
Each peak represents a fragment of the molecule
Peak on the far right represents the molecular ion
Molecular ion peak = relative formula mass of the molecule