C8

Question 1

What is a pure substance?

Answer 1

a single element or compound not mixed with any other substances

Question 2

How is it possible to distinguish pure substances and mixtures?

Answer 2

Pure elements and compounds melt and boil at specific temperatures

Question 3

What is a formulation?

Answer 3

a mixture that has been designed as a useful product. They are made by mixing components in carefully measured quantities

Question 4

Give examples of formulations

Answer 4

• Paints
• cleaning agents
• fertilisers
• alloys

Question 5

How do you calculate the Rf value?

Answer 5

distance moved by substance/ distance moved by solvent

Question 6

How does the chromatography of a mixture and a pure compound differ?

Answer 6

• a mixture separates into different spots depending on the solvent
• a pure compound will produce a single spot in all solvents

Question 7

Explain the test for hydrogen

Answer 7

(the squeaky pop test)

• a burning splint is held at the end of a test tube
• hydrogen present = will be a squeaky pop sound

Question 8

Explain the test for oxygen

Answer 8

uses a glowing splint inserted into a test tube of oxygen.
This will result in the splint relighting

Question 9

Explain the test for chlorine gas

Answer 9

Use damp litmus paper.
When the damp litmus paper is put in chlorine gas the paper is bleached white

Question 10

Explain the test for carbon dioxide

Answer 10

test for carbon dioxide involves aqueous calcium hydroxide (limewater).
When carbon dioxide is bubbled through the limewater it becomes cloudy

Question 11

What can be used to identify some metal cations? e.g. Lithium, sodium, potassium, calcium and copper

Answer 11

Flame tests

Question 12

What colour flame do lithium compounds result in?

Answer 12

a crimson flame

Question 13

Which metal compound results in a lilac flame?

Answer 13

potassium

Question 14

What colour flame do copper compounds result in?

Answer 14

a green flame

Question 15

Which metal compound results in a yellow flame?

Answer 15

sodium

Question 16

What colour flame do calcium compounds result it?

Answer 16

a orange-red flame

Question 17

What happens if a sample containing a mixture of ions is used?

Answer 17

Some flame colours may be masked

Question 18

What solution can be used to identify some cations?

Answer 18

Sodium hydroxide

Question 19

What is the formula for sodium hydroxide?

Answer 19

NaOH

Question 20

What hydroxide forms a white precipitate (a heavy white amorphous powder) at first but then dissolves in excess sodium hydroxide to form a colourless solution?

Answer 20

Aluminium

Question 21

What colour precipitate does a calcium solution form when NaOH is added?

Answer 21

white

Question 22

What colour precipitate does a copper solution form when NaOH is added?

Answer 22

blue

Question 23

What colour precipitate does a iron(ii) solution form when NaOH is added?

Answer 23

green

Question 24

What colour precipitate does a iron(iii) solution form when NaOH is added?

Answer 24

brown

Question 25

What colour precipitate does a magnesium solution form when NaOH is added?

Answer 25

white

Question 26

Write an ionic equation for precipitate formation for a metal ion of your choice

Answer 26

Ca₂+(aq) + 2OH-(aq) → Ca(OH)₂ (s) **Instructions:** metal ion + balanced hydroxide ion product- metal followed by (OH) with the same number used in the reactants

Question 27

What can help detect carbonates? Explain the process

Answer 27

Dilute acids react with carbonates to form carbon dioxide (gas) The carbon dioxide can be identified using limewater (calcium hydroxide)

Question 28

How can we identify sulfates?

Answer 28

adding a few drops of dilute hydrochloric acid (to get rid of carbonate ions) and then drops of barium chloride - sulfate ions in a solution will produce a white precipitate

Question 29

How do we identify halides?

Answer 29

Add a few drops of dilute nitric acid and then silver nitrate A coloured precipitate will be formed depending on the halide

Question 30

What colour precipitate is formed when chloride is identified?

Answer 30

white

Question 31

What colour precipitate is formed when bromide is identified?

Answer 31

cream

Question 32

What colour precipitate is formed when iodide is identified?

Answer 32

yellow

Question 33

How else can elements be identified and what are the benefits?

Answer 33

using instrumental methods - (accurate, sensitive and rapid)

Question 34

What is flame emission spectroscopy?

Answer 34

An example of an instrumental method used to analyse metal ions in solutions

Question 35

Explain the process of flame emission spectroscopy

Answer 35

- The sample is placed in a flame - As the ions heat up they move to higher energy levels and once the electrons drop back to their original energy level, they release energy as light - The light passes through a spectroscope and the output is a line spectrum - The line spectrum can be analysed to identify the metal ions in the solution and measure their concentrations