Topic 12 - Chemical Analysis

Question 1

How is a pure substance defined?

Answer 1

A pure substance is one that is made up of only one substance, this substance being either an element or a compound.

Question 2

What are fixed points of an element?

Answer 2

Melting and boiling points.

Question 3

Why are fixed points useful for chemical analysis?

Answer 3

Since you can heat a mixture to identify substances if you know their fixed points in relation to other substances.

Question 4

What are formulations?

Answer 4

A formulation is a mixture that has been designed to produce a useful product. Many consumer products are formulations.

Question 5

How are formulations used in medicine?

Answer 5

Medicinal drugs are formultions, often containing 5-10% of the active drug, which helps the body relieve sickness. If taken in tablet form, they can contain colourants, sweetners, smooth coatings amongst other things to aid swallowing.

Question 6

What two phases do chromatograms always contain?

Answer 6

A mobile phase and stationary phase.

Question 7

How does the mobile phase of a chromatogram work?

Answer 7

The mobile phase moves through the stationary phase, carrying the components of the mixture up with it. Each component will have a different attraction for the mobile and stationary phases. A substance with stronger forces of attraction between itself and the mobile phase than the stationary phase will be carrie a greater distance within a given time.

Question 8

What is the line drawn at the top of the chromatogram called?

Answer 8

The solvent front.

Question 9

What is an Rf value?

Answer 9

The retention factor value is a ratio calculated by dividing the distance a spot moves by the distance the solvent moves.

Question 10

How do you calculate Rf value?

Answer 10

Rf = distance moved by substance / distance moved by solvent

Question 11

What is the reaction for the test for hydrogen?

Answer 11

Zinc + Sulphate Acid –> Zinc Sulphate + Hydrogen

Question 12

What is the hydrogen test?

Answer 12

Hold a lighted splint where the hydrogen gas is meant to go and the splint will ‘pop’

Question 13

What is the reaction for the test for oxygen?

Answer 13

Hydrogen Peroxide ———-> Water + Oxygen
Manganese (IV) Oxide

Question 14

What is the oxygen test?

Answer 14

Take a glowing splint near to where the oxygen should come out of the apparatus, the glowing splint should relight.

Question 15

What is the reaction for the test for carbon dioxide?

Answer 15

Calcium Carbonate + Hydrochloric Acid –> Calcium Chloride + Water + Carbon Dioxide

Question 16

What is the carbon dioxide test?

Answer 16

Funnel the products of the reaction between marble chips and HCl into a limewater solution. If carbon dioxide is present the limewater will turn cloudy.

Question 17

What is the test for chlorine gas?

Answer 17

If you hold damp blue litmus paper where the chlorine gas will come out, it will turn white as it becomes bleached.

Question 18

In a flame test, what colour do Lithium ions (Li+) turn a bunsen flame?

Answer 18

Crimson/red

Question 19

In a flame test, what colour do Sodium ions (Na+) turn a bunsen flame?

Answer 19

Yellow

Question 20

In a flame test, what colour do Potassium ions (K+) turn a bunsen flame?

Answer 20

Lilac/purple

Question 21

In a flame test, what colour do Calcium ions (Ca2+) turn a bunsen flame?

Answer 21

Orange/red

Question 22

In a flame test, what colour do Copper ions (Cu2+) turn a bunsen flame?

Answer 22

Green

Question 23

How do you do a flame test?

Answer 23

A nichrome wire loop should be dipped in concentrated hydrochloric acid and then heated to clean it first.

Then it should be dipped in the acid again before dipping it into the metal compound.

Then hold the loop in the roaring blue flame of a Bunsen burner.

Use the colour of the flame to identify the metal ion in the compound.

Question 24

How does the precipitate reaction work?

Answer 24

Reacting unknown compounds with sodium hydroxide solution leads to a type of precipitate forming.

Question 25

What precipitate is formed in the precipitate reaction when Copper (II) ions are present?

Answer 25

A blue precipitate.

Question 26

What precipitate forms in the precipitate reaction when Iron (II) ions are present?

Answer 26

A green precipitate.

Question 27

What precipitate is formed in the precipitate reaction when Iron (III) ions are present?

Answer 27

A brown precipitate.

Question 28

What three ions form a white precipitate in the precipitate reaction when they are present?

Answer 28

Al3+ ions, Mg2+ ions, Ca2+ ions.

Question 29

How do you distinguish between Al3+ ions, Mg2+ ions and Ca2+ ions (since they all form a white precipitate)?

Answer 29

If the solution dissolves in the precipitation reaction they are Al3+ ions. If not then you test for them in the flame test. If there is no colour they are Mg2+ ions, if there is an orange/red colour they are Ca2+ ions.

Question 30

What is the general equation for carbonate reactions?

Answer 30

If you add a dilute acid to a carbonate, it fizzes and produces carbon dioxide gas.