Chemical Analysis - C8

Question 1

What are flame tests used to identify?

Answer 1

Flame tests can be used to identify some metal ions

Question 2

What do lithium compounds result in?

Answer 2

Crimson flame.

Question 3

What do sodium compounds result in?

Answer 3

Yellow flame

Question 4

What do Potassium compounds result in?

Answer 4

Lilac flame.

Question 5

What do Copper compounds result in?

Answer 5

Green flame.

Question 6

What do Calcium compounds result in?

Answer 6

Orange-Red flame.

Question 7

Why can some flame colours be masked?

Answer 7

A sample containing a mixture of ions is used.

Question 8

What can be used to identify some metal ions?

Answer 8

Sodium hydroxide.

Question 9

What do solutions of aluminium, calcium and magnesium ions form when sodium hydroxide solution is added?

Answer 9

White precipitates

Question 10

Why does aluminum differ from calcium and magnesium in relation to sodium hydroxide?

Answer 10

Aluminium hydroxide precipitate dissolves in excess sodium
hydroxide solution.

Question 11

What do solutions of copper(II), iron(II) and iron(III) ions form when sodium hydroxide solution is added?

Answer 11

Coloured precipitates.

Question 12

Copper(II) forms…

Answer 12

Blue precipitate.

Question 13

Iron (II) forms…

Answer 13

Green precipitate

Question 14

Iron(III) forms…

Answer 14

Brown precipitate

Question 15

Carbonates react with dilute acids to form…

Answer 15

Carbon dioxide gas.

Question 16

How can carbon dioxide be identified?

Answer 16

It turns limewater milky when bubbled through.

Question 17

How do you identify a halide?

Answer 17

Add dilute nitric acid and silver nitrate solution to your solution.

Question 18

Chloride forms…

Answer 18

White precipitate.

Question 19

Bromide forms…

Answer 19

Cream precipitate.

Question 20

Iodide forms…

Answer 20

Yellow precipitate.

Question 21

What do sulfate ions in solution with barium chloride solution in the presence of dilute hydrochloric acid?

Answer 21

White precipitate.

Question 22

What is a pure substance?

Answer 22

A single element or compound,
not mixed with any other substance.

Question 23

What do pure elements and compounds melt and boil at?

Answer 23

Specific temperatures.

Question 24

What do impure elements and compounds melt and boil at?

Answer 24

lower melting point, higher boiling point at a range of temperatures

Question 25

What does a pure substance mean in everyday language?

Answer 25

A substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk.

Question 26

What is a formulation?

Answer 26

A mixture that has been designed as a useful product.

Question 27

Many formulation (products) are what?

Answer 27

Complex mixtures in which each
chemical has a particular purpose.

Question 28

How are formulations made?

Answer 28

By mixing the components in carefully measured quantities to ensure that the product has the required properties

Question 29

Examples of formulations…

Answer 29

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

Question 30

Why do we use chromatography?

Answer 30

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

Question 31

What are the two stages of chromatography?

Answer 31

A stationary phase and a mobile phase.

Question 32

What is an Rf value?

Answer 32

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.

Question 33

Rf Value equation

Answer 33

Dissolved substance / solvent

Question 34

How can chromatographic methods be used for distinguishing pure substances from impure substances?

Answer 34

Run a pure sample of that mixture next to the unknown substance. If the Rf values of the reference and one of the spots in the mixture match, the substance may be present.

Question 35

Test for hydrogen

Answer 35

If you hold a lit splint at the open end of a test tube containing hydrogen, you’ll get a “squeaky pop”.

Question 36

Test for oxygen

Answer 36

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

Question 37

Test for chlorine

Answer 37

When damp litmus paper is
put into chlorine gas the litmus paper is bleached and turns white.

Question 38

Why do we use instrumental methods?

Answer 38

To detect and identify elements and compounds.

Question 39

Advantages of instrumental methods.

Answer 39

Very accurate, very sensitive, very rapid and determines concentration of ions.

Question 40

What is flame emission spectroscopy?

Answer 40

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

Question 41

How does flame emission spectroscopy?

Answer 41

The sample is put into a flame and the light given out is passed
through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.

Question 42

Why is flame emission spectroscopy accurate?

Answer 42

The combination of wavelengths emitted by an ion depends on its charge. Sincet line spectrum. no two ions have the same charge and the same electron arrangement, different ions emit different wavelengths of light. So each ion produces a different pattern of wavelengths, and has a differen