C8 - Chemical Analysis

Question 1

Define a pure substance

Answer 1

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

Question 2

How can we use melting and boiling point data to determine if a substance is pure?

Answer 2

Pure elements and compounds melt and boil at specific temperatures.

Question 3

Describe what is meant by a formulation

Answer 3

A complex mixture that has been designed as a useful product.

(The quantity of each component is carefully measured so the product has the properties we need.)

Question 4

Describe how paper chromatography can be used to identify substances in a mixture.

Answer 4

The compounds in a mixture may separate into different spots depending on the solvent.

Question 5

Suggest how chromatographic methods can be used for distinguishing pure substances from impure substances.

Answer 5

A pure substance produces one spot on the chromatogram.

An impure substance produces two or more spots.

Question 6

What is the equation for calculating Rf Value?

Answer 6

Rf = distance moved by substance
________________________________
distance moved by solvent

Question 7

Test for Hydrogen

Answer 7

Hold a burning splint at the open end of a test tube of gas.
Hydrogen burns rapidly with a pop sound.

Question 8

Test for Oxygen

Answer 8

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

Question 9

Test for carbon dioxide

Answer 9

Uses an aqueous solution of calcium hydroxide (lime water).
When carbon dioxide is shaken/bubbled through limewater it turns cloudy.

Question 10

Test for chlorine

Answer 10

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

Question 11

Flame tests: Lithium compound

Answer 11

Results in a crimson flame

Question 12

Flame tests: Sodium compounds

Answer 12

Result in a yellow flame

Question 13

Flame tests: Potassium compounds

Answer 13

Result in a lilac flame

Question 14

Flame tests: Calcium compounds

Answer 14

Result in an orange-red flame

Question 15

Flame tests: Copper compounds

Answer 15

Result in a green flame

Question 16

Describe flame emission spectroscopy

Answer 16

An instrumental method used to analyse metal ions in solutions.

Question 17

3 advantages to instrumental methods

Answer 17

Accurate - More likely to identify a metal ion correctly than a flame test

Sensitive - Works even on a tiny sample of metal compound

Rapid - Faster than flame tests