(Topic 8) Chemical Analysis (CGP Book)

Question 1

What is meant by purity?

Answer 1

Nothing has been added, so it is in it’s natural state

Question 2

What is a pure substance in chemistry?

Answer 2

Only contains one compound or element throughout

Question 3

How to test how pure a substance is?

Answer 3

• Measure it’s melting or boiling point and compare how close it is to the boiling or melting point of the pure substance
• closer you measurement, the purer your substance

Question 4

What happens if a substance is impure?

Answer 4

• lower melting point and increased melting point range
• increased boiling point resulting in boiling at a range of temperatures

Question 5

What are formulations?

Answer 5

Mixtures with exact amounts of compnents

Question 6

What is a pigment?

Answer 6

A formulation that gives paint a colour

Question 7

What is a solvent?

Answer 7

A formulation that is used to dissolve other components and alter the viscosity

Question 8

What is binder?

Answer 8

A formulation that forms a film that holds pigment in place

Question 9

What is an additive?

Answer 9

A formulation added to further change physical and chemical properties of paint

Question 10

What is the mobile phase in chromatography?

Answer 10

• molecules can move. Always liquids or gases

Question 11

What is stationary phase in chromatography?

Answer 11

Molecules can not move. In a solid or really thick liquid

Question 12

During paper chromatography, what does the amount of time the molecules spend in each phase depend on?

Answer 12

• how soluble they are in the solvent
• how attracted they are to the paper

Question 13

How to calculate rf values in chromatography?

Answer 13

Distance travelled by substance / distance travelled by solvent

Question 14

How to test for chlorine?

Answer 14

Damp litmus paper becomes bleached

Question 15

How to test for oxygen?

Answer 15

Glowing splint inside test tube, if oxygen present, the splint will relight

Question 16

How to test for carbon dioxide?

Answer 16

Bubbling carbon dioxide through limewater causes solution to turn cloudy

Question 17

How to test for hydrogen?

Answer 17

Lit splint at opening of test tube containing hydrogen, you will get squeaky pop

Question 18

How to test for carbonates?

Answer 18

Put a sample in a test tube
Use dropping pipette to add a couple of drops of dilute acid
Connect test tube to a test tube of limewater
If carbonate ions present, carbon dioxide released to turn limewater cloudy

Question 19

How to test for sulfate?

Answer 19

Use dropping pipette to add a couple of drops of dilute hydrochloric acid
Followed by couple drops of barium chloride solution to a test tube containing sample
If sulfate ions present, a white precipitate of barium sulfate will form

Question 20

How to test for halide ions?

Answer 20

Add a couple drops of dilute nitric acid
Followed by couple drops of silver nitrate solution

Question 21

What does a chloride give when testing for halides with nitric acid and silver nitrate?

Answer 21

A white precipitate of silver chloride

Question 22

What does a bromide give when testing for halides with nitric acid and silver nitrate?

Answer 22

Cream precipitate of silver bromide

Question 23

What does an iodide give when testing for halides with nitric acid and silver nitrate?

Answer 23

Yellow precipitate of silver iodide

Question 24

What colour are lithium ions (Li+) under a flame?

Answer 24

Crimson flame

Question 25

What colour does sodium (Na+) give in a flame?

Answer 25

Yellow flame

Question 26

What colour do potassium ions (K+) give in a flame?

Answer 26

Lilac flame

Question 27

What colour do calcium ions (Ca2+) give in a flame?

Answer 27

Orange/red flame

Question 28

What colour do copper ions (Cu2+) give in a flame?

Answer 28

Green flame

Question 29

What colour precipitate do you get if Calcium (Ca2+) is mixed with sodium hydroxide?

Answer 29

White

Question 30

What colour precipitate do you get if Copper (Cu2+) is mixed with sodium hydroxide?

Answer 30

Blue

Question 31

What colour precipitate do you get if Iron (II) (Fe2+) is mixed with sodium hydroxide?

Answer 31

Green

Question 32

What colour precipitate do you get if Iron (III) (Fe2+) is mixed with sodium hydroxide?

Answer 32

Brown

Question 33

What colour precipitate do you get if Aluminium (Al3+) is mixed with sodium hydroxide?

Answer 33

White

Question 34

What colour precipitate do you get if Magnesium (Mg2+) is mixed with sodium hydroxide?

Answer 34

White

Question 35

How to test for insoluble hydroxides using sodium hydroxide to make a precipitate?

Answer 35

Add a few drops of sodium hydroxide to a solution of your sample solution

Question 36

Process of flame emission spectroscopy?

Answer 36

• Sample placed in flame
• As ions heat up, electrons gain energy and when they drop back to original energy levels, they transfer energy as light
• Light passes through spectroscope which produces a line spectrum
• Combination of wavelengths emitted by an ion depends on it’s charge and electron arrangement so each one is different
• Intensity of spectrum indicates concentration of that ion in solution
• can be used to identify mixtures

Question 37

Process of flame tests?

Answer 37

• Clean a platinum wire loop by dipping in antiseptic and flaming it
• Dip loop into sample and put back in flame. Record colour