Chemical Analysis

Question 1

What is a pure substance?

Answer 1

A pure substance is a single element or compound, not mixed with any other substance

Question 2

What is a formulation and how is it made?

Answer 2

• a formulation is a mixture of compounds in measured quantities that has been designed as an useful product
• formulation include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
• e.g. alloys are mixtures of metals; they are harder than pure metals, so have a particular purpose

Question 3

Describe paper chromatography

Answer 3

• a start line is drawn near the bottom of the paper. The mixture is spotted on the line
• a beaker is filled with small amount of solvent (it cannot touch or go above the start line when paper is placed in a beaker)
• paper is hung on a rod and placed in a beaker
• solvent travels up the paper, thus separating the components
• before solvent level reaches the end, the paper is taken out and the finish line is marked, the paper is dried
• the procedure works when different compounds have different affinities for the solvent/paper. Stronger attraction for the paper - travels slowly with the solvent

Question 4

What is the stationary phase in chromatography?

Answer 4

the absorbent paper

Question 5

What is the mobile phase in chromatography?

Answer 5

A solvent

Question 6

How is Rf calculated?

Answer 6

Distance moved by the spot / distance moved by the solvent

Question 7

Describe the test for hydrogen

Answer 7

Pop with burning splints over gas

Question 8

Describe the test for oxygen

Answer 8

Glowing splint relights

Question 9

Describe the test for carbon dioxide

Answer 9

Turns limewater milky

Question 10

Describe the test for chlorine

Answer 10

Bleaches damp litmus paper and makes it white

Question 11

Describe the flame test results

Answer 11

Lithium compounds -> crimson red flame
Sodium compounds -> yellow flame
Potassium compounds -> lilac flame
Calcium compounds -> orange red flame
Copper compounds -> green flame

Question 12

Describe the sodium hydroxide test results

Answer 12

Copper(II) forms a blue precipitate
Iron(II) forms a dirty green precipitate
Iron(III) forms a brown precipitate
Al(3+), Ca(2+) and Mg(2+) form white precipitate but only the Al(OH)3 dissolves in excess NaOH to form a colourless solution

Question 13

Describe the test for carbonate anions

Answer 13

Add dilute acid e.g. HCl
Fizzing observed, as CO2 is released

Question 14

Describe the test for sulfate anions

Answer 14

Add a solution containing Ba(2+) cations e.g. a solution of BaCl2
White precipitate of BaSo4 forms
(!!!) can also be though of a test for barium (II); add sulfates - white precipitate forms

Question 15

Describe silver nitrate tests

Answer 15

Add a solution of AgNo3
- chloride -> white precipitate, silver chloride
- bromide -> cream precipitate, silver bromide
- iodides -> yellow precipitate, silver iodide

Question 16

What are instrumental methods?

Answer 16

They are accurate, sensitive and rapid methods which are useful when the amount of sample is very small

Question 17

Describe the flame emission spectroscopy

Answer 17

• instrumental method used for identifying metal ions in solution or measuring their concentration
• spectroscope measures the exact wavelength of the light emitted by a metal ion
• that allows for definite identification -> sometimes colour are difficult to distinguish
• concentration are found by measuring the intensity of light emitted. The more intense light, the greater the concentration of the metal ion in a solution
• from the intensity vs concentration graph, you can read off a relevant concentration value at a given intensity

Question 18

What are cations?

Answer 18

Positive ions

Question 19

What are anions.

Answer 19

Negative ions

Question 20

What is mixture?

Answer 20

A combination of two or more substances that aren’t chemically combined

Question 21

What is a formulation?

Answer 21

A mixture that has been designed for a specific purpose

Question 22

What is the melting/boiling point of pure substance?

Answer 22

A single defined temperature

Question 23

What are what is the melting/boiling point of mixtures?

Answer 23

A range of temperatures

Question 24

What is the melting point of pure water?

Answer 24

0 °C

Question 25

What is the boiling point of pure water?

Answer 25

100 °C

Question 26

What are some examples of formulations?

Answer 26

Paint, processed food, fuels, cleaning products and cosmetics

Question 27

What is the test for purity?

Answer 27

Test melting/boiling point

Question 28

What are nanoparticles?

Answer 28

Lumps of substance that are 1-100 nanometers in size

Question 29

What are nanoparticles in formulations?

Answer 29

Useful in formulation as you can use less

Question 30

How do you test you see if water is pure?

Answer 30

Test of boiling point is exactly 100 °C

Question 31

What is the flame test?

Answer 31

A method of identifying a metal ion by the colour it produces in a roaring flame

Question 32

What is the test for halide ions?

Answer 32

Add nitric acid and silver nitrate solution

Question 33

What does precipitate mean?

Answer 33

An insoluble solid that forms from a solution during a chemical reaction

Question 34

What are the advantages of instrumental methods?

Answer 34

• accurate
• sensitive
• rapid

Question 35

What are the disadvantages of instrumental methods?

Answer 35

• expensive
• require training
• must compare results to known samples

Question 36

What are the advantages of flame emission spectroscopy?

Answer 36

• can spot multiple ions
• can find ion concentration