Chemical Changes

Question 1

What are the 5 types of physical changes?

Answer 1

• Forming a mixture
• Change of state
• Change of size
• Heating/lighting effect of electricity
• Magnetic effect of electricity

Question 2

State a difference between a physical and chemical change.

Answer 2

Physical change: No formation of new substances, properties of substance remains the same before and after change, none or little heat is taken in or given off.
Chemical change: Formation of new substances is present, properties of ending products are different from starting products, a lot of heat is taken in and given off.

Question 3

What are the 5 causes of chemical change?

Answer 3

• Mixing
• Heat
• Oxygen
• Light
• Electricity

Question 4

What are the two chemical changes by heat?

Answer 4

Combination and thermal decomposition.

Question 5

What is combination?

Answer 5

2 or more substances combined to form a new substance with heat.

Question 6

What is thermal decomposition?

Answer 6

Breaking down of a substance into 2 or more simpler substances by heat.

Question 7

What are the 3 chemical changes by oxygen?

Answer 7

• Rusting
• Combustion/oxidation
• Cellular respiration

Question 8

What is combustion/oxidation?

Answer 8

Combination of a substance with oxygen with the presence of heat.

Question 9

What is cellular respiration?

Answer 9

Living cells or plants and animals taking in oxygen to release the energy stored in glucose.

Question 10

What are the 2 chemical changes by light?

Answer 10

• Photosynthesis

- X-ray film

Question 11

What are the 2 chemical changes by electricity?

Answer 11

• Electrolysis

- Electroplating

Question 12

What is electrolysis?

Answer 12

Chemical decomposition of substances with the presence of an electric current.

Question 13

What is electroplating?

Answer 13

Coating a substance with metal with a passage of an electric current.

Question 14

What are some strong types of acids?

Answer 14

Hydrochloric acid, sulfuric acid and nitric acid.

Question 15

What are some types of weak acids?

Answer 15

Malic acid, citric acid and ethanoic acid.

Question 16

What are the properties of acids?

Answer 16

• Corrosive
• Turns blue litmus paper red, red litmus paper remains red.
• Reacts with metals, carbonates and alkalis.
• pH value <7
• Dissolve in water
• Conduct electricity
• Tastes sour

Question 17

What are some types of strong alkalis?

Answer 17

Sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia hydroxide, magnesium hydroxide.

Question 18

What is sodium hydroxide used for?

Answer 18

Make soaps and detergents.

Question 19

What is potassium hydroxide used for?

Answer 19

Remove paints.

Question 20

What are the properties of alkalis?

Answer 20

• Corrosive
• Turns red litmus paper blue, blue litmus paper remains blue
• Reacts with acids and ammonium salts
• pH value >7-14
• Dissolves in water
• conducts electricity
• Feels soapy and tastes bitter

Question 21

State one similarity and difference between alkalis and acids.

Answer 21

Similarity: Both are corrosive/conduct electricity/dissolves in water.
Difference: Acids turn blue litmus paper red but alkalis turns red litmus paper blue/alkalis feels soapy and tastes bitter but acids tastes sour.

Question 22

What is the chemical product of the reaction metal + acids?

Answer 22

Salt + hydrogen

Question 23

What is the chemical product of the reaction carbonate + acid?

Answer 23

Salt + carbon dioxide + water

Question 24

What is the chemical product of the reaction alkali + acid?

Answer 24

Salt + water

Question 25

What happens when carbon dioxide is present in lime water?

Answer 25

White precipitate is formed, metal becomes smaller, effervescence of colourless, odourless gas evolved, increase in temperature and lighted splint extinguishes with a ‘pop’ sound.

Question 26

What happens when hydrogen is present in lime water?

Answer 26

Metal becomes smaller, effervescence of colourless, odourless gas evolved, increase in temperature and lighted splint extinguishes.

Question 27

How does an indicator work?

Answer 27

An indicator is a substance which changes colour depending on whether the solution being tested is acidic or alkaline.

Question 28

What is the pH value and colour of detergent?

Answer 28

Violet, pH 14.

Question 29

What is the pH value and colour of distilled water?

Answer 29

Green, pH 7.

Question 30

What are the 5 beneficial uses of effects of chemical change?

Answer 30

- Decomposition - Fuel combustion - Cooking - Production of materials, medicine and fertilisers - Natural processes such as reproduction, digestion, growth and photosynthesis

Question 31

What are the 5 harmful effects of chemical change?

Answer 31

- Air pollution - Acid rain - Rusting - Decomposition

Question 32

What is the harmful and useful effect of fuel combustion?

Answer 32

Harmful: Releases air pollutants into the atmosphere - gases such as sulfur dioxide dissolves in rain, which corrodes buildings and other structures. Polluted air results in difficulty breathing and risk of respiratory illnesses. Useful: Releases energy to more vehicles.

Question 33

What does acid rain do?

Answer 33

It is resulted from fuel combustion destroys plants and kills fishes and other aquatic life.

Question 34

What is rusting?

Answer 34

When iron rusts, structures such as bridges become corroded can be unsafe. Rusting causes loss of finite natural resources.

Question 35

What is the harmful and useful effect of decomposition?

Answer 35

Harmful: Waste of food supply and resources. Useful: Breaks down unwanted matter and releases nutrients back to earth to prevent too many dead organisms from piling up on earth.