C12 - Chemical Analysis - Complete

Question 1

What is meant by purity in chemistry and how does this differ from in commercial cases?

Answer 1

In commercial cases, ‘pure’ means nothing added to it, whereas in chemistry ‘pure’ means solely one substance. This substance can be a compound or element, but not a mixture.

Question 2

How can you separate different substances?

Answer 2

By testing them at their boiling and melting points

Question 3

What do impurities tend to do to a substance?

Answer 3

Lower its melting point and raise its boiling point

Question 4

What is formulation?

Answer 4

A mixture that has been designed to produce a useful product

Question 5

Give two examples of formulations

Answer 5

Paint, drugs, washing-up liquids, fuels, alloys, pesticides, cosmetics and food products

Question 6

How do you detect amino acids in a chromatogram since they are colourless?

Answer 6

You spray it with a locating agent and they will turn purple

Question 7

What differs in chromatography that separates the substances?

Answer 7

The amounts of attraction to the paper and the solvent that separates them differs: allowing the mixtures to be separated into many different fractions

Question 8

Why is retention factor used?

Answer 8

So that different substances can be compared and identified with each other on a database, were it would impractical to store pictures or actual chromatograms to compare

Question 9

What is the equation for retention factor?

Answer 9

Retention factor = distance moved by substance / distance moved by solvent

Question 10

How must you keep the chromatography experiments the same each time?

Answer 10

They must be at the same temperature and with the same solvent each time

Question 11

Why can’t you test a mixture of metal ions with a flame test?

Answer 11

As one of their colours may be masked by the other ions

Question 12

What false must you use for flame tests?

Answer 12

Roaring blue flame

Question 13

What precautions must be taken with the nichrome wire loop before you use it for a flame test?

Answer 13

It must be dipped in hydrochloric acid before into the substance, and then heated to get rid of any contamination, and then dipped into he hydrochloric acid again before into the substance

Question 14

What three ions form a white precipitate with sodium hydroxide?

Answer 14

Mg 2+, Ca 2+ and Al 3+

Question 15

How do you distinguish between the 3 white precipitates formed by sodium hydroxide?

Answer 15

Aluminium dissolves if more sodium hydroxide is added, and then the other two can be distinguished by a flame test - magnesium gives no colour and calcium gives a brick red

Question 16

What colour precipitate is formed when sodium hydroxide is added to Copper (II) ions?

Answer 16

Blue

Question 17

What colour precipitate is formed when sodium hydroxide is added to Iron (II) ions?

Answer 17

Green

Question 18

What colour precipitate is formed when sodium hydroxide is added to Iron (III) ions?

Answer 18

Reddish brown

Question 19

What colour do Potassium ions give in a flame test?

Answer 19

Lilac

Question 20

What colour do Lithium ions give in a flame test?

Answer 20

Crimson red

Question 21

What colour do Calcium ions give in a flame test?

Answer 21

Brick red

Question 22

What colour do Sodium ions give in a flame test?

Answer 22

Yellow

Question 23

What colour do Copper ions give in a flame test?

Answer 23

Green

Question 24

How can you test for a carbonate?

Answer 24

You add dilute acid to it and it produces carbon dioxide

Question 25

Why does CO2 turn limewater milky?

Answer 25

As the acidic carbon dioxide reacts with the alkaline sodium hydroxide in the limewater - creating a white precipitate: turning it milky

Question 26

How do you test for the halides?

Answer 26

First you add dilute nitric acid, and then you add silver nitrate. If a precipitate forms, halide ions are present

Question 27

What are the halides?

Answer 27

Chlorides, bromides and iodides

Question 28

Which precipitate do iodide ions create in dilute nitric acid and silver nitrate?

Answer 28

Yellow

Question 29

Which precipitate do chloride ions create in dilute nitric acid and silver nitrate?

Answer 29

White

Question 30

Which precipitate do bromide ions create in dilute nitric acid and silver nitrate?

Answer 30

Cream

Question 31

How can you test for a sulphate in a solution?

Answer 31

Add dilute hydrochloric acid and then barium chloride. If the precipitate is white, a sulphate is present

Question 32

Why do you add dilute hydrochloric acid before the barium chloride when you test for sulphates?

Answer 32

So that any carbonate ions that are present that would otherwise react with the barium

Question 33

What are 2 benefits of modern instrumental methods?

Answer 33

They are faster / They are more accurate and sensitive / They enable tiny samples to be analysed

Question 34

What are 2 negatives of modern instrumental methods?

Answer 34

They are often very expensive / They take special training to use / They give results that can often be interpreted in comparison with known substances

Question 35

How does flame emission spectroscopy work?

Answer 35

When the different metal ions are heated, their electrons become excited and jump energy levels. When they return to their original level, the energy is released as light. Flame emission spectroscopy analyses the wavelengths of this light and uses them to compare to a database of existing results. By doing so, it can find what ion was burned and in what concentration it was

Question 36

Give one example of where flame emission spectroscopy is used

Answer 36

In the steel industry, where the amounts of each particle present in the alloy must be monitored carefully / In large water companies to make sure the water they are providing is safe