bab 5.1 water Flashcards
Characteristics of pure water? (5)
Boiling point = 100C
Melting / Freezing point = 0C
No colour, odour, taste
Density = 1gcm^-3 at 4C
Poor heat & electric conductor
What is surface tension?
Result of cohesive force between molecules of water at the surface
Why can daddy longlegs stay afloat on water?
Surface tension
What is capillary action?
Cohesive force between water molecules & adhesive force between water molecules and cell wall of xylem, water draw up from roots to leaves of plant
What is cohesive force?
Attrative force between same molecules
What is adhesive force?
Attractive force between different molecules
What is the composition of water?
Made of 2 hydrogen atoms and 1 oxygen atom
How to determine the composition of water?
Electrolysis
What is electrolysis?
Process of decomposition of water into hydrogen and oxygen using electrical energy
What gas is produces at the electrodes during electrolysis?
Pos. electrode (Anode): Oxygen
Neg. electrode (Cathode): Hydrogen
What is the ratio of oxygen to hydrogen after performing electrolysis?
1:2
Why is dilute hydrochloric acid added into distilled water during electrolysis?
Because distilled water is a poor conductor of electricity
What test is used to determine the gasses produced at the electrodes after electrolysis?
Confirmatory gas test
What are the results of the confirmatory gas test at both electrodes?
Pos. electrode/Anode (Oxygen): Glowing wooden splinter lights up
Neg. electrode/Cathode (Hydrogen): Burning wooden splinter is extinguished and produce a ‘pop’ sound
What are the effects of impurities into water? (4)
Changes taste, smell and colour
Reduces freezing point
Increases boiling point
Increases density
What is evaporation?
Process that happens at the surface of water that changes water to water vapour at any temperature
How does evaporation happen?
The molecules of water at the surface have higher kinetic energy, thus they can move faster and escape into the air
What substance is used to absorb water vapour in the air when studying the effect of humidity to water evaporation?
Anhydrous calcium chloride
(Anhydrous means containing no water)
What is used to test if water is present?
Cobalt chloride paper
What are the relation of humidity with water evaporation?
Dry air contains less water vapour, thus it can hold more water molecules that escape from the water’s surface
Evaporation rate increases
What happens when cobalt chloride paper touches water?
The paper turns from a blue colour to a pink colour
What is the use of a filament lamp when studying the effect of surrounding temperature to water evaporation?
To increase the surrounding temperature because filament lam produces heat energy
What is the relation of surrounding temperature with water evaporation?
When surrounding temperature increases, water molecules at the surface gain more energy, move faster and escape into the air easily
Evaporation rate increases
Why is filter paper folded into halves and quarters when studying the effect of exposed surface area to water evaporation?
To decrease the exposed surface area
