8. Chemical analysis

Question 1

In chemistry what is a “pure” substance?

Answer 1

A substance made of a single element or compound

Question 2

How can pure substances be distinguished from impure ones?

Answer 2

By their melting/boiling points

Question 3

Describe the melting and boiling points of pure substances

Answer 3

One very specific temperature

Question 4

Describe the melting and boiling points of impure substances

Answer 4

They change state at a range of temperatures

Question 5

What is a formulation?

Answer 5

A complex mixture designed as a useful product

Question 6

Give three examples of formulations

Answer 6

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

Question 7

In paper chromatography, what is the stationary phase and what is the mobile phase

Answer 7

Paper is stationary, solvent (usually water or ethanol) is mobile

Question 8

How can chromatography show the difference between pure and impure substances?

Answer 8

Pure ones will not separate into a number of spots

Question 9

How is the Rf value calculated?

Answer 9

distance moved by spot/distance moved by solvent

Question 10

In chromatography, why must the substances be placed on a pencil line?

Answer 10

Pencil will not dissolve in the solvent

Question 11

In chromatography why must the solvent height be lower than the pencil line?

Answer 11

So that the substances do not dissolve into the solvent off the paper

Question 12

How can hydrogen be tested for?

Answer 12

Makes a squeaky pop when a splint is placed in it

Question 13

How can oxygen be tested for?

Answer 13

Relights a glowing splint

Question 14

How can carbon dioxide be tested for?

Answer 14

Bubble through limewater, turns it milky (cloudy)

Question 15

How can chlorine be tested for?

Answer 15

Bleaches damp litmus paper white

Question 16

What is the colour of the flame produced from a lithium containing compound?

Answer 16

Crimson

Question 17

What is the colour of the flame produced from a copper containing compound?

Answer 17

Green

Question 18

What is the colour of the flame produced from a sodium containing compound?

Answer 18

Yellow

Question 19

What is the colour of the flame produced from a potassium containing compound?

Answer 19

lilac

Question 20

What is the colour of the flame produced from a calcium containing compound?

Answer 20

Orange-red

Question 21

Which solutions produce white precipitates on addition of sodium hydroxide?

Answer 21

Solutions containing aluminium, magnesium, calcium ions

Question 22

What is the test for carbonates?

Answer 22

Add an acid to generate carbon dioxide gas

Question 23

What is the test for halides?

Answer 23

Add silver nitrate and nitric acid to generate a solid silver halide precipitate

Question 24

What is the test for sulfate ions?

Answer 24

Add barium chloride and hydrochloric acid, forms white precipitate

Question 25

How is flame emissions spectroscopy carried out?

Answer 25

Sample placed in a flame, light emitted is passed through a spectroscope to give a spectrum which can be compared to a reference