Chapter 11 Science Workbook

Question 1

What will happen if sodium hydroxide solution is added to dilute hydrochloric acid

Answer 1

A colourless solution is formed

Question 2

What will happen if the mixture in the beaker is heated strongly?

Answer 2

The mixture will boil to dryness, leaving behind a white solid

Question 3

Explain why antacids can be used to relieve the discomfort caused by excess acid in the stomach

Answer 3

Antacids contain alkaline compounds which can neutralise the excess acids in the stomach

Question 4

A piece of magnesium was added to dilute hydrochloric acid observe what happened

Answer 4

Effervescence was formed and the magnesium ribbon becomes smaller and finally disappears

Question 5

Light a wooden split and place it at the mouth of the test tube with hydrochloric acid and magnesium ribbon observe what happened

Answer 5

A ‘pop’ sound was heard

Question 6

Calcium carbonate was put into a test tube of hydrochloric acid observe what happened

Answer 6

White precipitate was observed in limewater

Question 7

What gas was given off when hydrochloric acid was added to magnesium

Answer 7

Hydrogen

Question 8

What happened (observations) to sugar after it was heated for 2 min and what happened after 5 min

Answer 8

2 min: the sugar melted to form a colourless solution
5 min: the colourless liquid turned into a brown substance and a sweet smell was detected

Question 9

What can chemical changes result from (4)and what does it usually involve (1)

Answer 9

Mixing of substances
Exposure to heat
Light
Electricity

Involves transfer of energy

Question 10

How does neutralisation of acid on teeth by toothpaste benefit us

Answer 10

It prevents tooth decay

Question 11

What is the benefit of release of energy from food?

Answer 11

Energy released from food via respiration allows us to carry out daily activities

Question 12

Harmful effect of decay of apple

Answer 12

Food poisoning OR cause of wastage of food

Question 13

Harmful effect of rusting of iron components

Answer 13

It causes metal structures to weaken

Question 14

Harmful effect of combustion

Answer 14

Combustion of fuels releases carbon dioxide into the atmosphere and pollutes the environment and causes health problems

Question 15

What does galvanising with zinc prevent?

Answer 15

Rusting of iron components

Question 16

What does vacuum packaging prevent

Answer 16

Decay of an apple

Question 17

Explain why the reaction (neutralisation) is a chemical change

Answer 17

The formation of new substances (potassium chloride and water) indicates that the reaction is a chemical change

Question 18

Explain whether evaporation is a physical or chemical change

Answer 18

Physical change, the conversion of water to water vapour only involves a change in state and no new substances are formed.

Question 19

Describe how the pH value changed when dilute sulfuric acid was added to the alkali in the beaker until the universal indicator turned green

Answer 19

The pH value in the beaker was above 7 when the universal indicator was first added to potassium hydroxide. The pH decreases as more dilute sulfuric acid was added until it reached pH 7 when potassium hydroxide was neutralise by sulfuric acid.