Topic 5: Chemical Changes

Question 1

What are the two types of changes

Answer 1

Physical and Chemical

Question 2

What is the difference between Physical and Chemical change

Answer 2

Physical changes: are reversible and do not involve
the formation of new substances

Chemical changes are irreversible, and result from
chemical interactions. They when matter interacts with heat, light or electricity; two or more different kinds of matter interact

Question 3

List 3 chemical changes

Answer 3

• Interactions between matter when mixed
• Interactions between matter and heat
• Thermal decomposition
• Interactions between matter and oxygen (Rusting/Oxidation)
• Combustion

Question 4

What’s the difference between Oxidation and Combustion

Answer 4

Oxidation: substance reacts with oxygen
Combustion: refers to the combination of a substance with oxygen in the presence of heat.

Question 5

Define acids

Answer 5

An acid is a substance that produces hydrogen ions in aqueous solution

Question 6

What is the formula for:
- hydrochloric acid
- nitric acid
- sulfuric acid
- phosphoric acid

Answer 6

• HCl
• HNO3
• H2SO4
• H3PO4

Question 7

Define the basicity of an acid

Answer 7

The basicity of an acid is the number of hydrogen ions, which can be produced by one molecule of the acid.

Question 8

List the 5 properties of acids

Answer 8

Acids:
- have sour taste.
- have pH less than 7.
- turn blue litmus paper red (no effect on red litmus paper).
- turn universal indicator from green to yellow / orange / red (depending on its pH).
- are good conductors of electricity in aqueous solution as they contain mobile ions

Question 9

What is formed when Acids react with reactive metals

Answer 9

Salt and hydrogen gas

Question 10

What is formed when Acids react with metal carbonate

Answer 10

Form salt, water and carbon dioxide

Question 11

Define bases

Answer 11

Any metal oxide or hydroxide that reacts with an acid to produce a salt
and water only

Question 12

What is formed when Acids react with bases

Answer 12

Forms salt and water only

Question 13

Describe the test for hydrogen gas

Answer 13

Test tube with magnesium ribbon in dilute hydrochloric acid. Place a lighted splint at the mouth of the test tube.

Question 14

Describe the test for carbon dioxide gas

Answer 14

Bubble gas into limewater (aqueous calcium hydroxide). CO2 form white precipitate with limewater

Question 15

Describe the test for ammonia gas

Answer 15

Test gas with damp red litmus paper. Ammonia gas turns the paper blue

Question 16

Define Alkalis

Answer 16

A substance that produces hydroxide ions
in aqueous solution.

Question 17

List 5 properties of Alkalis

Answer 17

Alkalis:
- have bitter taste and soapy feel.
- have pH greater than 7.
- turn red litmus paper blue (no effect on blue litmus paper).
- turn universal indicator from green to blue / violet. (depending on its pH).
- are good conductors of electricity in aqueous solution as they contain mobile ions.

Question 18

What forms when alkalis react with acids

Answer 18

Salt and water only

Question 19

What forms when alkalis are heated with ammonia gas

Answer 19

Produce salt, water and ammonia gas