Topic 8 - Chemical analysis:

Question 1

A pure substance:

Answer 1

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

• They melt and boil at specific temperatures
• The mp and bp of the pure substances can be used to distinguish them from mixtures

Question 2

Test for hydrogen:

Answer 2

• Use a burning splint
• A squeaky pop can be heard

Question 3

Test for oxygen:

Answer 3

• Use a glowing splint
• The splint should relight

Question 4

Test for carbon dioxide:

Answer 4

• Bubble the gas through limewater
• Turns milky 🥛

Question 5

Test for chlorine:

Answer 5

• Use damp litmus paper
• Litmus paper becomes bleached and turns white

Question 6

Flame test colours (used to identify metal ions):

Answer 6

🟥 Lithium-crimson
🟨 Sodium- yellow
🟪 Potassium- lilac
🟧 Calcium- orange
🟩 Copper- green

Leave crimson soap yellow potatoes lilac curd orange AND copper green.

Question 7

Formulation:

Answer 7

A mixture that has been designed as a useful product

Question 8

Rf value:

Answer 8

Rf value= Distance moved by substance/Distance moved by solvent

Question 9

Chromatography:

Answer 9

Purpose- to separate mixtures

• The more soluble a substance is, the further up the paper it travels

Question 10

Sample containing a mixture of ions:

Answer 10

Flame colours are masked (you cannot see them)

Question 11

Metal hydroxides (reaction with NaOH):

Answer 11

• Aluminium, calcium and magnesium all form a white precipitate with NaOH
• Only aluminium’s precipitate dissolves with excess NaOH
• Copper (II) produces a blue precipitate 🟦
• Iron (II) produces a green precipitate 🟩
• Iron (III) produces a brown percipitate 🟫

Question 12

Carbonates:

Answer 12

• Carbonates react with dilute acids to create carbon dioxide
• The gas is bubbled through limewater, if carbon dioxide is present, the limewater turns cloudy ☁

Question 13

Test for halides:

Answer 13

• First add nitric acid, followed by silver nitrate solution
  Chloride- white precipitate
  Bromide- cream precipitate
  Iodine- yellow precipitate
• Cats with brains can ideally yodel

Question 14

Test for sulfates:

Answer 14

• First add dilute hydrochloric acid, followed by barium chloride soloution
• A white precipitate will form when sullfate ions are present

Question 15

Instrumental methods:

Answer 15

• Elements and compounds can be detected using instrumental methods
• Thety are accurate, sensetive and rapid- making them advantageous compared to chemical tests

Question 16

Flame emission spectroscopy:

Answer 16

• An example of an instrumental method- used to analyse metal ions in a solution
• A sample is put into a flame- the light given out is passed through spectroscope
• The output is a line spectrum- can be analysed to identify the metal ions in the solution and measure their concentrations

Question 17

Method for chromatoography:

Answer 17

Method
* Draw (pencil) start line on chromatography paper
* Place spot of food colouring on start line
* Place solvent in beaker
* Place chromatography paper in beaker / container
* So (chromatography) paper is in solvent, but solvent is below start line
* Use a lid
* Wait for solvent to travel up the chromatography paper (until
near top)
* Mark solvent front
* Dry the (chromatography) paper

Measurements
* Measure distance between start line and centre of spot
* Use of measurements to determine Rf value