Topic 8 - Chemical analysis

Question 1

What is formulation and some examples?

Answer 1

A mixture that has been designed as a useful product.
Fuels, Foods, Fertilisers

Question 2

How are formulations made?

Answer 2

Mix together components that have a particular purpose in carefully measured quantities - ensuring the product has the properties required.

Question 3

What is chromatography used for and where is it useful?

Answer 3

Separate mixtures.
Chromatography can be useful when trying to identify substances.

Question 4

What are the two different phases in chromatography?

Answer 4

The mobile phase - The solvent that carries the different substances.
The stationary phase - The non-moving phase for example the chromatography paper.

Question 5

How do we identify unknown substances using chromatography and what is the equation?

Answer 5

Question 6

Does the rf change by solvent?

Answer 6

Yes, different solvents change the Rf value.

Question 7

How do mixtures separate in chromatography?

Answer 7

They separate into different spots depending on the solvent.

Question 8

What do pure compounds produce in chromatography?

Answer 8

They produce a single spot in all the solvents.

Question 9

How do you test for hydrogen gas?

Answer 9

Hold a lit splint at the end of a test tube containing gas. If hydrogen is present you will hear a squeaky pop sound.

Question 10

How do you test for oxygen gas?

Answer 10

Hold a glowing splint inside a test tube containing gas you want to test. If oxygen is present the splint will relight.

Question 11

How do you test for carbon dioxide gas?

Answer 11

Bubble the gas through lime water. If lime water is present the lime water turns cloudy/milky.

Question 12

How do you test for chlorine gas?

Answer 12

Put the damp blue litmus paper into the gas. If chlorine is present litmus paper is bleached and turns white.

Question 13

What are flame tests used for?

Answer 13

They can be used to identify some metal ions.

Question 14

What is the general method for flame tests?

Answer 14

Dip a clean wire loop into a solid sample to be tested. Put the loop in a bunsen burners blue flame. Observe the flame colour.

Question 15

In the flame test if the flame is crimson what ion is present?

Answer 15

Lithium Li+

Question 16

In the flame test if the flame is yellow what ion is present?

Answer 16

Sodium Na+

Question 17

In the flame test if the flame is lilac what ion is present?

Answer 17

Potassium K+

Question 18

In the flame test if the flame is orange-red what ion is present?

Answer 18

Calcium Ca²⁺.

Question 19

In the flame test if the flame is green what ion is present?

Answer 19

Copper Cu²⁺

Question 20

What is the problem when identifying metal ions in samples that contain mixture of ions?

Answer 20

Flame colours can be masked.

Question 21

How do we test when metal ions are in solutions and how do you carry it out?

Answer 21

Use the sodium hydroxide test.
Add sodium hydroxide to the solution that is being tested. If metal ions is present a precipitate with a colour will form. You have to observe the colour.

Question 22

When aluminium is reacted with sodium hydroxide what is the product and what colour is the precipitate.

Answer 22

Product - Aluminium hydroxide
Colour - White

Question 23

When Calcium is reacted with sodium hydroxide what is the product and what colour is the precipitate.

Answer 23

Product - Calcium Hydroxide
Colour - White

Question 24

When magnesium is reacted with sodium hydroxide what is the product and what colour is the precipitate.

Answer 24

Product - Magnesium hydroxide
Colour - White

Question 25

When copper(II) is reacted with sodium hydroxide what is the product and what colour is the precipitate.

Answer 25

Product - Copper hydroxide Colour - Blue

Question 26

When iron(II) is reacted with sodium hydroxide what is the product and what colour is the precipitate.

Answer 26

Product - Iron(II) hydroxide Colour - Green

Question 27

When iron(III) is reacted with sodium hydroxide what is the product and the ionic equation and what colour is the precipitate.

Answer 27

Question 28

Since all aluminum, calcium and magnesium ions form white precipitate when added to sodium hydroxide how can you know if aluminum ions are present?

Answer 28

Only aluminum hydroxide precipitate will dissolve when an excess of sodium hydroxide is added.

Question 29

How do you test for carbonate ions?

Answer 29

React the carbonated with dilute acid this forms carbon dioxide gas. Bubble the gas through lime water. If carbonate was present and carbon dioxide was formed the lime water will turn cloudy/milky.

Question 30

How do you test for halide ions?

Answer 30

Add nitric acid and silver nitrate to the solution. If ions are present a different precipitate will form depending on the halide.

Question 31

When chlorine is reacted with silver nitrate what colour is the precipitate and what is the product formed?

Answer 31

Colour - White Product - Silver chloride

Question 32

When bromide is reacted with silver nitrate what colour is the precipitate and what is the product formed?

Answer 32

Colour - Cream Product - Silver Bromide

Question 33

When iodide is reacted with silver nitrate what colour is the precipitate and what is the product formed??

Answer 33

Colour - Yellow Product - Silver iodide

Question 34

How do you test for sulfate ions?

Answer 34

Add barium chloride solution and dilute hydrochloric acid. If sulfate ions are present white precipitate forms.

Question 35

What are other ways elements and compounds can be detected and the benefits?

Answer 35

Using instrumental methods. They are accurate. They are sensitive They are rapid

Question 36

What is flame emission spectroscopy and how does it work?

Answer 36

It is an instrumental method used to analyse metal ions in solutions. A sample is put into a flame. The light emitted is passed through a spectroscope. The spectroscope gives a line spectrum that can be analysed to identify the metal ions in solution. The concentrations of the metal ions in solution can be found.