bab 5.1 water

Question 1

Characteristics of pure water? (5)

Answer 1

Boiling point = 100C
Melting / Freezing point = 0C
No colour, odour, taste
Density = 1gcm^-3 at 4C
Poor heat & electric conductor

Question 2

What is surface tension?

Answer 2

Result of cohesive force between molecules of water at the surface

Question 3

Why can daddy longlegs stay afloat on water?

Answer 3

Surface tension

Question 4

What is capillary action?

Answer 4

Cohesive force between water molecules & adhesive force between water molecules and cell wall of xylem, water draw up from roots to leaves of plant

Question 5

What is cohesive force?

Answer 5

Attrative force between same molecules

Question 6

What is adhesive force?

Answer 6

Attractive force between different molecules

Question 7

What is the composition of water?

Answer 7

Made of 2 hydrogen atoms and 1 oxygen atom

Question 8

How to determine the composition of water?

Answer 8

Electrolysis

Question 9

What is electrolysis?

Answer 9

Process of decomposition of water into hydrogen and oxygen using electrical energy

Question 10

What gas is produces at the electrodes during electrolysis?

Answer 10

Pos. electrode (Anode): Oxygen
Neg. electrode (Cathode): Hydrogen

Question 11

What is the ratio of oxygen to hydrogen after performing electrolysis?

Answer 11

1:2

Question 12

Why is dilute hydrochloric acid added into distilled water during electrolysis?

Answer 12

Because distilled water is a poor conductor of electricity

Question 13

What test is used to determine the gasses produced at the electrodes after electrolysis?

Answer 13

Confirmatory gas test

Question 14

What are the results of the confirmatory gas test at both electrodes?

Answer 14

Pos. electrode/Anode (Oxygen): Glowing wooden splinter lights up
Neg. electrode/Cathode (Hydrogen): Burning wooden splinter is extinguished and produce a ‘pop’ sound

Question 15

What are the effects of impurities into water? (4)

Answer 15

Changes taste, smell and colour
Reduces freezing point
Increases boiling point
Increases density

Question 16

What is evaporation?

Answer 16

Process that happens at the surface of water that changes water to water vapour at any temperature

Question 17

How does evaporation happen?

Answer 17

The molecules of water at the surface have higher kinetic energy, thus they can move faster and escape into the air

Question 18

What substance is used to absorb water vapour in the air when studying the effect of humidity to water evaporation?

Answer 18

Anhydrous calcium chloride
(Anhydrous means containing no water)

Question 19

What is used to test if water is present?

Answer 19

Cobalt chloride paper

Question 20

What are the relation of humidity with water evaporation?

Answer 20

Dry air contains less water vapour, thus it can hold more water molecules that escape from the water’s surface
Evaporation rate increases

Question 21

What happens when cobalt chloride paper touches water?

Answer 21

The paper turns from a blue colour to a pink colour

Question 22

What is the use of a filament lamp when studying the effect of surrounding temperature to water evaporation?

Answer 22

To increase the surrounding temperature because filament lam produces heat energy

Question 23

What is the relation of surrounding temperature with water evaporation?

Answer 23

When surrounding temperature increases, water molecules at the surface gain more energy, move faster and escape into the air easily
Evaporation rate increases

Question 24

Why is filter paper folded into halves and quarters when studying the effect of exposed surface area to water evaporation?

Answer 24

To decrease the exposed surface area

Question 25

What is the relation of exposed surface area with water evaporation?

Answer 25

Larger exposed surface area allows more water molecules to escape
Evaporation rate increases

Question 26

What is the use of the fan when studying the effect of air movement to water evaporation?

Answer 26

The fan transports the water vapour released from the water surface to another place

Question 27

What is the relation of air movement with water evaporation?

Answer 27

Air sweeps away water vapour in the air. High speed of wind causes air at the water surface to dry
Evaporation rate increases

Question 28

Compare evaporation and boiling
(2)

Answer 28

• The change from liquid to gas
• Absorbs heat energy

Question 29

Contrast evaporation and boiling (4)

Answer 29

Evaporation: Boiling:
- Any temperature - At boiling point
- Slow - Fast
- On surface - Throughout liquid
- Effected by 4 factors - Not affected by 4 factors