8. Chemical Analysis

Question 1

What is a pure substance?

Answer 1

Made up of just one substance - either an element or a compound

Question 2

How are properties changed when impurities are introduced?

Answer 2

• conductivity
• strength
• melting and boiling point

Question 3

What happens when salt is added to pure water?

Answer 3

The salt dissolve to produce an impure substance (salt lowers the temperature of ice) so melts the ice

Question 4

Difference between melting/boiling point between pure and impure substances?

Answer 4

Pure substances melt at a specific temperature whereas impure substances can melt or boil at a range of temperatures

Question 5

How does melting point of an impure substance compare to that of a pure one?

Answer 5

Impure substances have lower melting points than pure substances

Question 6

What is a formulation?

Answer 6

A mixture of compounds/substances that do not react with each other but produce a mixture to suit a particular use

Question 7

Examples of formulations?

Answer 7

Toothpaste, moisturiser, make up, alloys, paint, medicines

Question 8

What does pure mean in advertising?

Answer 8

Nothing else has been added to the product

Question 9

What are some different types of food additives?

Answer 9

Preservatives, colourings, flavour enhancers

Question 10

What is chromatography?

Answer 10

A technique for separating mixtures into their components in order to analyse, identify, purify the mixture or components

Question 11

What is the mobile phase in chromatography?

Answer 11

The solvent (e.g. water)

Question 12

What is the stationary phase in chromatography?

Answer 12

The paper

Question 13

What is Rf factor?

Answer 13

Distance substances move up the paper in a certain amount of time

Question 14

How to work out Rf factor?

Answer 14

Distance moved by substance / distance moved by solvent

Question 15

What is the solvent front?

Answer 15

Point at which water stops moving up the paper

Question 16

What is the centre spot?

Answer 16

Point at which a band or spot of colour is

Question 17

What is the baseline?

Answer 17

Line where original sample was placed

Question 18

How is chlorine tested for?

Answer 18

Electrolysis

Question 19

How is carbon dioxide tested for?

Answer 19

Limewater turns cloudy

Hydrochloric acid + calcium carbonate

Question 20

How is oxygen tested for?

Answer 20

Glowing splint relights

Hydrogen peroxide -> water + oxygen

Question 21

How is hydrogen tested for?

Answer 21

Squeaky pop test

Mg + HCl -> MgCl + H2

Question 22

Ways to test for positive ions?

Answer 22

Flame test and sodium hydroxide/precipitate test

Question 23

What is the flame test?

Answer 23

Using the colour of the Bunsen flame to identify the metal ion in the compound

Question 24

What does a crimson flame show?

Answer 24

Lithium present

Question 25

What does a yellow flame show?

Answer 25

Sodium present

Question 26

What does a lilac flame show?

Answer 26

Potassium present

Question 27

What does a red flame show?

Answer 27

Calcium present

Question 28

What do the flame colours show is present?

Answer 28

Crimson - lithium Yellow - sodium Lilac - potassium Red - calcium

Question 29

How to carry out the precipitate test?

Answer 29

Add 1cm3 of NaOH solution, if precipitate is white add an excess of NAOH solution

Question 30

What do coloured precipitates show in the sodium hydroxide test?

Answer 30

Blue - copper Green - iron (II) Brown - iron (III)

Question 31

What does a blue precipitate show in a test for positive ions?

Answer 31

Copper present

Question 32

What does a green precipitate show in a test for positive ions?

Answer 32

Iron (II) present

Question 33

What does a brown precipitate show in a test for positive ions?

Answer 33

Iron (III) present

Question 34

What does a white precipitate show in a test for positive ions?

Answer 34

Either aluminium, calcium or magnesium

Question 35

What does a soluble white precipitate show in a test for positive ions?

Answer 35

Aluminium present

Question 36

What does an insoluble white precipitate show in a test for positive ions?

Answer 36

Either calcium or magnesium present

Question 37

What is a halide?

Answer 37

A charged halogen

Question 38

What are the tests for negative ions?

Answer 38

Halide test, carbonate test and sulphate test

Question 39

What is the halide test?

Answer 39

Add dilute nitric acid and silver nitrate solution - if precipitate forms a halide is present

Question 40

What does a yellow precipitate show in the halide test?

Answer 40

Iodide ions present

Question 41

What does a cream precipitate show in the halide test?

Answer 41

Bromide ions present

Question 42

What does a white precipitate show in the halide test?

Answer 42

Chloride ions present

Question 43

What is the sulphate test?

Answer 43

Add dilute HCl then barium chloride soliton - white precipitate show sulphate ions present

Question 44

What does a white precipitate show in the sulphate test?

Answer 44

Shows sulphate ions are present

Question 45

What is the carbonate test?

Answer 45

Add dilute HCl - bubbles produced = use teat pipette to transfer gas produced to limewater - limewater milky means carbonate ions present

Question 46

What does milky limewater mean in the carbonate test?

Answer 46

Carbonate ions are present

Question 47

How can substances be analysed?

Answer 47

Using a methods including paper chromatography, gas chromatography, mass spectrometry and flame emission spectroscopy

Question 48

How is flame emission spectroscopy carried out?

Answer 48

Sample is put into flame and then the light given off is passed through a spectroscope

Question 49

What is the output in flame emission spectroscopy?

Answer 49

A line spectrum that can be analysed to identify metal ions and concentration

Question 50

Advantages of flame emission spectroscopy?

Answer 50

* quick * accurate * sensitive - only requires a small sample * brightness of spectrum = concentration

Question 51

Disadvantages of flame emission spectroscopy?

Answer 51

* destructive- sample being tested is burned | * only identifies presence of elements not compounds

Question 52

Application of flame emission spectroscopy?

Answer 52

* quality control in chemical manufacture * working out composition of distant stars * drug detection