Topic 8 - chemical analysis

Question 1

Define a pure substance

Answer 1

A substance that only contains one type of element or compound

Question 2

Define what a formulation is

Answer 2

Mixtures that have been prepared using a specific formula which is designed as a useful product

Question 3

What is a physical test to test the purity of a substance?

Answer 3

Testing for their boiling points, testing physical properties of that substance

Question 4

What are chemical tests for testing the purity of a substance?

Answer 4

Reacting the substance with another chemical

Question 5

What effect will impurities have on the boiling and melting points of a compound?

Answer 5

Impurities increase the boiling point of a substance, and may also result in it boiling over a range of temperatures, but it will lower the melting points

Question 6

Describe a test for chlorine

Answer 6

Chlorine bleaches damp litmus paper, turning it white if it is a positive test

Question 7

Describe a test for oxygen

Answer 7

• if you put a glowing splint inside a test tube containing oxygen
• the oxygen will relight the glowing splint if a positive test

Question 8

Describe a test for carbon dioxide

Answer 8

• bubbling carbon dioxide through ( or shaking carbon dioxide with) an aqueous solution of calcium hydroxide (known as limewater) causes the solution to turn cloudy if a positive test

Question 9

Describe a test for hydrogen

Answer 9

• if you hold a burning splint at the open end of a test tube containing hydrogen, you’ll get a “squeaky pop” if a positive test
  (The noise comes from the hydrogen burning quickly in the oxygen in the air to form water)

Question 10

Tests for metal ions in flames and their colours

Answer 10

Lithium - crimsen
Sodium - yellow
Potassium - lilac
Calcium - orange-red
Copper - green

Question 11

What happens when you add sodium hydroxide solution to aluminium, calcium and magnesium?

Answer 11

Aluminium hydroxide - forms a white precipitate but then dissolves back
Calcium hydroxide - white precipitate
Magnesium hydroxide - white precipitate

Question 12

What is a precipitate?

Answer 12

When you mix two liquids to get a solid

Question 13

What are the outcomes when testing sodium hydroxide with copper II, iron II and iron III?

Answer 13

Copper II - blue
Iron II - green
Iron III - brown

Question 14

How do we test for halides?

Answer 14

By using silver nitrate and dilute nitric acid

Question 15

Describe what happens when you use silver nitrate and dilute nitric acid with chlorine, bromine and iodine

Answer 15

Silver chloride - white
Silver bromide - cream
Silver iodide - yellow

Question 16

What’s the test for sulfate ions?

Answer 16

Sulfate ions in solution produce a white precipitate with barium chloride and hydrochloric acid

Question 17

Describe two differences between flame emission spectroscopy and flame tests

Answer 17

Flame emission spectroscopy can be done with mixtures that contain different metal ions, whilst in flame tests it can only be done with substances containing one metal ion
Flame emission spectroscopy is very accurate and not subjective to the human eye, whilst for flame tests, the result is dependant on the opinion of the person observing the colour