10. Qualitative Analysis

Question 1

Define reagent

Answer 1

A suns stance added to a reaction mixture to bring about a chemical reaction

Question 2

Define precipitate

Answer 2

An insoluble solid formed in solution as the result of a chemical reaction in the solution

Question 3

Define suspension

Answer 3

A cloudy mixture containing small particles of an insoluble solid distributed throughout a liquid

Question 4

Define miscible

Answer 4

Used to describe liquids that mix in all proportions and will form a single layer

Question 5

Define effervescence

Answer 5

Describes the release of gas from a reaction mixture

Question 6

Define evolved

Answer 6

Used to describe the release of energy or matter from a reaction mixture

Question 7

Define pungent

Answer 7

Sharp acidic odours

Question 8

Describe the tests for water

Answer 8

• Add water to anhydrous copper (II) sulfate > white to blue

- add water to anhydrous cobalt (II) chloride > blue to pink

Question 9

Describe the test for carbon dioxide

Answer 9

Pass through limewater (calcium hydroxide solution) > limewater changes from colourless to milky (CaCO3). If CO2 is in excess, milky ppt dissolves to give colourless solution (Ca(HCO3)2)

Question 10

Describe the test for hydrogen

Answer 10

Put burning splint in sample of gas > gives squeaky pop

Question 11

Describe the test for oxygen

Answer 11

Put glowing splint in sample of gas > splint relights

Question 12

Describe the tests for ammonia

Answer 12

• damp universal indicator paper > turns blue

- glass rod dipped in conc HCl > white fumes

Question 13

Describe the test for Hydrochloric acid

Answer 13

• damp universal indicator paper turns red

- glass rod dipped in conc NH3 solution > white fumes

Question 14

Describe the test for chlorine

Answer 14

Damp litmus/universal indicator paper - turns red then bleaches

Question 15

What does a white crystalline solid indicate about a substance’s chemical composition?

Answer 15

Doesn’t contain transition metal ions

compound of group I, II or ammonium compound

Question 16

What does a blue crystalline solid indicate about a substance’s chemical composition?

Answer 16

Possibly contains Cu^2+ ions

Question 17

What does a pale green crystalline solid indicate about a substance’s chemical composition?

Answer 17

Possibly contains Fe^2+ ions

Question 18

What does a red-brown crystalline solid indicate about a substance’s chemical composition?

Answer 18

Possibly contains Fe^3+ ions

Question 19

If a substance dissolves to form a colourless solution, what does that indicate about its chemical composition?

Answer 19

Soluble in water

Compound of group I, II, aluminium, zinc or ammonium

Question 20

If a substance dissolves to form a blue solution, what does that indicate about its chemical composition?

Answer 20

Soluble in water

Possibly contains Cu^2+ ion

Question 21

If a substance dissolves to form a pale green solution, what does that indicate about its chemical composition?

Answer 21

Soluble in water

Possibly contains Fe^2+ ion

Question 22

If a substance dissolves to form a yellow/orange solution, what does that indicate about its chemical composition?

Answer 22

Soluble in water

Possibly contains Fe^3+ ion

Question 23

If a substance doesn’t dissolve in water, what does that indicate about its chemical composition?

Answer 23

Insoluble in water

Question 24

If a flame test yields a crimson flame, what does that indicate about the substance’s chemical composition?

Answer 24

Could contain Li^+ ion

Question 25

If a flame test yields a brick red flame, what does that indicate about the substance’s chemical composition?

Answer 25

Could contain Ca^2+ ion

Question 26

If a flame test yields a yellow-orange flame, what does that indicate about the substance’s chemical composition?

Answer 26

Could contain Na^+ ion

Question 27

If a flame test yields an apple green flame, what does that indicate about the substance’s chemical composition?

Answer 27

Could contain Ba^2+ ion

Question 28

If a flame test yields a lilac flame, what does that indicate about the substance’s chemical composition?

Answer 28

Could contain K^+ ion

Question 29

What colour is a K^+ flame if viewed behind cobalt glass?

Answer 29

Pink

Question 30

If a flame test yields a blue-green flame, what does that indicate about the substance’s chemical composition?

Answer 30

Could contain Cu^2+ ion

Question 31

What is the chemical test for iodine?

Answer 31

Add a few drops of starch solution > will turn blue-black of iodine present

Question 32

What are the chemical tests for the ammonium ion?

Answer 32

- add solid to test tube with dilute sodium hydroxide. Warm gently and test evolved gas with damp universal indicator paper > pungent smell, indicator paper turns blue (NH3 evolved from action of alkali on ammonium compound) - expose to glass rod dipped in conc HCl > white smoke

Question 33

What is the chemical test for halides?

Answer 33

- dissolve sample in deionised water and add dilute nitric acid and a few drops of silver nitrate solution. - chloride > white ppt (AgCl) - soluble in dilute and conc ammonia solution to form colourless solution - bromide > cream ppt (AgBr) - not soluble in dilute ammonia, soluble in conc ammonia to form colourless solution - iodide > yellow ppt (AgI) - insoluble in both dilute and conc ammonia solution

Question 34

What is the chemical test for sulfate ions?

Answer 34

- dissolve solid in deionised water. Add dilute nitric acid followed by barium chloride (or nitrate) solution and shake to mix - if sulfate ion present, white precipitate (BaSO4) forms

Question 35

What is the chemical test for carbonate ions?

Answer 35

- dissolve solid in deionised water. Add dilute nitric acid and collect any gas evolved with a pipette. Bubble contents of pipette through limewater - if carbonate present, colourless gas evolved and limewater turns from colourless to milky white (due to CO2)