Chemical Analysis

Question 1

Test for Hydrogen

Answer 1

• Hold a lighted splint at the end of an open test tube
• If a popping sound it produced, hydrogen is present

Question 2

Test for Oxygen

Answer 2

• Insert a glowing splint into the mouth of a flask
• If the splint relights, oxygen is present

Question 3

Test for Carbon Dioxide

Answer 3

• Bubble carbon dioxide gas through limewater
• If the limewater turns cloudy, carbon dioxide is present

Question 4

Test for Chlorine

Answer 4

• Hold a piece of damp blue litmus paper to the mouth of a boiling tube
• If the paper turns red then white, chlorine is present

Question 5

Why does the litmus paper turn red before turning white?

Answer 5

• Chlorine dissolves in the water on the litmus paper
• Reacts with it to form HCL
• HCL is acid so it turns the paper red

Question 6

Test for Cations (Flame Test)

Answer 6

• Take a nichrome wire loop and dip it in the unknown solution
• Hold the loop over a blue flame
• Observe what colour the flame turns

Question 7

What colour does Lithium (Li+) produce?

Answer 7

Crimson

Question 8

What colour does Sodium (Na+) produce?

Answer 8

Yellow

Question 9

What colour does Potassium (K+) produce?

Answer 9

Lilac

Question 10

What colour does Calcium (Ca2+) produce?

Answer 10

Orange-Red

Question 11

What colour does copper (Cu2+) produce?

Answer 11

Green

Question 12

Test for Cations (Metal Hydroxide Test)

Answer 12

• Add sodium hydroxide to the metal ion
• If a coloured precipitate forms it could be 1 one of 3 cations
• If a white precipitate forms, add excess sodium hydroxide
• If it dissolves, Al3+ is present, if not its Mg2+ or Ca2+

Question 13

Metal Hydroxide Precipitate Colours

Answer 13

• Fe3+ - Brown
• Fe2+ - Green then turns brown
• Cu2+ - Light blue

Question 14

Test for Carbonates

Answer 14

• Add dilute HCL to carbonates
• Run any gas produced in limewater through a tube
• If carbonates are present then the limewater will turn cloudy

Question 15

Test for Sulfates

Answer 15

• Add barium chloride to dilute HCL
• If a white precipitate forms sulfate is present

Question 16

Test for Halides

Answer 16

• Add silver nitrate to dilute nitric acid
• If a coloured precipitate forms, a halide is present

Question 17

Halide Precipitate Colours

Answer 17

• Iodide (I-) - Yellow
• Bromide (Br-) - Cream
  Chloride (Cl-) - White

Question 18

What is a pure substance

Answer 18

• All the particles are the same
• Contains only one element/compound
• Has a fixed melting and boiling point

Question 19

What is the difference between the term pure in advertising and a pure substance?

Answer 19

• Pure in advertising means the product has nothing added to it and its in its natural state
• A pure substance is made up of only one element or compound

Question 20

What is a formulation?

Answer 20

A mixture of different components each with different jobs that work together to give the formulation specific properties

Question 21

What is an emulsion?

Answer 21

A mixture of 2 things which won’t usually mix together and a special chemical called an emulsifier that makes them stick together, e.g. mayonnaise

Question 22

How can you tell when a substance isn’t pure?

Answer 22

When it’s melting and boiling points are a range instead of a specific value

Question 23

Physical Test

Answer 23

When you test the physical properties of a substance

Question 24

What do impurities do to the melting and boiling points of substances?

Answer 24

• Decrease melting points
• Increase boiling points

Question 25

Paper Chromatography

Answer 25

Used to separate mixtures of soluble substances

Question 26

Paper Chromatography Method

Answer 26

- Draw a base line in PENCIL at the bottom of a sheet of filter paper - Draw a dot of the ink sample on the base line - Fill a beaker with a shallow amount of solvent (usually water or ethanol) making sure the ink and the base line don't come into contact with it - Place a lid on the beaker so the solvent doesn't evaporate - As the solvent seeps up the paper the present dyes dissolve in it and move up the paper

Question 27

Chromatogram

Answer 27

The result of separating mixtures by chromatography

Question 28

Mobile Phase

Answer 28

- A substance molecules can move in - Is always a liquid or a gas - In paper chromatography it's the solvent

Question 29

Stationary Phase

Answer 29

- A substance molecules can't move in - Is a solid but sometimes a thick liquid - in paper chromatography it's the paper

Question 30

Where do soluble chemical spend more time?

Answer 30

The mobile phase (they move faster)

Question 31

Where do insoluble chemical spend more time?

Answer 31

The stationary phase (they move slower)

Question 32

RF Value

Answer 32

Distance travelled by substance/Distance travelled by solvent

Question 33

What does the chromatogram of a pure substance look like?

Answer 33

- Doesn't separate as it only contains one substance - Leaves a single dot on the filter paper - Different papers and solvents produce different RF values

Question 34

Flame Emission Spectroscopy

Answer 34

- When metal ions are heated they emit light - The wavelength of light emitted (and the colour emitted as a result) is specific for certain metal ions

Question 35

Advantages of Flame Emission Spectroscopy

Answer 35

- If a sample contains multiple metal ions, the spectrum shows the wavelength of all of them - Thickness of the lines show the concentration of the ion - More accurate - More sensitive - Faster than regular flame test

Question 36

Manual Tests vs Instrumental Methods

Answer 36

- Manual - Basic but cheaper - Instrumental - Expensive but more accurate results