Chemical analysis

Question 1

What is a pure substance?

chemistry definition

Answer 1

a single element or compound not mixed with any other substances

Question 2

Describe melting and boiling points of pure substances

Answer 2

• melt and boil at specific temperatures

- solidify and condense at these temperatures

Question 3

What is the definition of pure substance, in everyday language?

Answer 3

a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state

Question 4

What is an impure substance?

Describe melting and boiling points

Answer 4

mixtures

they do not melt and boul at one temperature - they change state over a range of temperatures

they lower the melting point, increase the melting range of your substances,

increase boiling point, boils at a range of temperatures

Question 5

What is a formulation?

Answer 5

a mixture that has been designed as a useful product

Most are complex mixtures in which each chemical has a particular purpose.

Question 6

How are formulations made?

Answer 6

Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.

Question 7

What do formulations include? (7)

Answer 7

fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

Question 8

What is chromatography used for?

Answer 8

used to separate mixtures and can give information to help identify substances.

Question 9

What does separation in chromatography depend on?

Answer 9

the distribution of substances between the mobile and stationary phrase

Question 10

What is the mobile phase?

Answer 10

the solvent (often water)

molecules can move

Question 11

What is the stationary phase?

Answer 11

the absorbent paper

does not move

Question 12

What happens during chromatography in terms of phases?

Answer 12

the substances in the sample constantly move between the mobile and stationary phases = an equilibrium is formed between the two phases

Question 13

What does the distance up the chromatography paper depend on?

Answer 13

the attraction for the paper and for the solvent

Question 14

The chemicals that spend more time in the mobile phase than the stationary phase…..

Answer 14

will move further through the stationary phrase

Question 15

What type of molecules spend more time in the mobile phase?

Answer 15

• molecules with a higher solubility in the solvent and is less attracted to the paper

Question 16

What does the amount of time the molecules spend in each phase depend on?

Answer 16

• how soluble they are

- how attracted they are to the paper

Question 17

What is the equation for the Rf value?

Answer 17

distance moved by substance/ distance moved by solvent

Question 18

What are the properties and test for hydrogen?

Answer 18

• colourless, combines violently with oxygen when ignited

The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.

Question 19

What are the properties and test for oxygen?

Answer 19

• colourless, helps fuels burn more readily than in ai

The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen

Question 20

What are the properties and test for Co2?

Answer 20

• colourless
• The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with bubbled through limewater the limewater turns milky (cloudy).
• connect test tube with a test tube of limewater

Question 21

What is the test for Chlorine?

Answer 21

The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.

Question 22

What are the different ways you can identify metal ions (cations)

Answer 22

• flame tests

- sodium hydroxide solution

Question 23

What are the colours produced in a flame test for :

• lithium
• sodium
• potassium
• calcium
• copper

Answer 23

• lithium compounds result in a crimson flame
• sodium compounds result in a yellow flame
• potassium compounds result in a lilac flame
• calcium compounds result in an orange-red flame
• copper compounds result in a green flame.

Question 24

Name the colour of precipitate produced for each of these metals when they are added to sodium hydroxide solution:

• aluminium
• calcium
• magnesium
• copper (III)
• iron (II)
• iron (III)

Answer 24

Solutions of aluminium, calcium and magnesium ions form white precipitates

only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution

Copper(II) forms a blue precipitate,

iron(II) a green precipitate
iron(III) a brown precipitate.

Question 25

How to test for carbonates?

Answer 25

Carbonates react with dilute acids to form carbon dioxide gas ( +salt and water)

Carbon dioxide can be identified with limewater.

Question 26

What are carbonates and its properties?

Answer 26

carbonates are substances that contains CO3 (2-) ions

most are insoluble

sodium carbonate and potassium carbonate are soluble and dissolvable in water to form solutions that contain carbonate ions

Question 27

How to test for Halides?

Answer 27

Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid.

Add a couple of drops of dilute nitric acid, followed by a couple of drops of silver nitrate solution to your unknown solution

Question 28

What colour precipitate do silver chloride, silver bromide and silver iodide form?

Answer 28

Silver chloride is white,
silver bromide is cream
silver iodide is yellow.

Question 29

How do you test for sulfates

Answer 29

Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.

use a pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution to a test tube containing an unknown solution

Question 30

What are the advantages of instrumental methods compared with chemical tests

Answer 30

accurate, rapid and sensitive

can be used on small samples

Question 31

What is flame emission spectroscopy?

How does it work?

Answer 31

Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions.

The sample is put into a flame and the light given out is passed through a spectroscope.

During flame spectroscopy as the ions heat up, their electrons become excited. When the electrons drop back to their original energy levels, they transfer energy as light

Question 32

What can flame emisson spectroscopy be used to analyse?

Answer 32

• identify the metal ions in the solution

- measure their concentrations.