1. Water
The Solvent
of Life

2. How much of our planet is water?
How much of you is water?

3. 75% of the earth’s surface, 70% of all living things Why?
70% of earth’s surface is covered with water
96.5% of water is in the ocean
Water cycle 0 water is constantly moving from one form to another….

4. Where did the water come from?

5. What makes water so special?

6. Water is small, polar, and forms hydrogen bonds with other polar substances
Canadian Version Bonding in differentphases of water

7. The polarity of water molecules results in hydrogen bonding
The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond
Each water molecule can form hydrogen bonds with up to 4 neighbours

8. Special properties you shpuld understand
Water’s thermal properties:
high specific heat capacity
high heat of vaporisation
High latent heat of freezing
High latent heat of condensation
2. Cohesion, adhesion, surface tension
3. (solid) ice is less dense than (liquid) water

9. Water has a high specific heat capacity since its polar molecules are connected by hydrogen bonds

10. Specific heat capacity
If matter absorbs thermal energy, then unless it is melting or boiling, its temperature rises
Some materials have a greater capacity for absorbing thermal energy than others
We measure the ability of matter to absorb thermal energy using the term specific heat capacity (c, Jkg°C-1)
C = the energy required to raise the temperature of 1 kg of substance by 1 °C

11. Definition of specific heat capacity
The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C.

12. Calculating specific heat capacity (NOT required for your test!)
E = m × c × θ
E is the energy transferred in joules, J
m is the mass of the substances in kg
c is the specific heat capacity in J / kg °C
θ (‘theta’) is the temperature change in degrees Celsius, °C

13. Specific heat capacity
Some materials have a greater capacity for absorbing thermal energy than others

15. Water’s high specific heat impacts our climate
Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
Water can absorb or release huge amounts of heat energy with only a slight change in its own temperature
Large bodies of water (oceans, lakes) absorb heat during the day, release heat at night
Coastal temperatures remain relatively constant
Animation

16. A lot of energy must be put in (or given out) when water changes phase

17. Water has a high latent heat of vaporisation

18. Latent heat (of phase change)
The specific latent heat of a substance is a measure of how much heat energy is needed to change its phase.
For any substance, there is a specific heat of melting, vaporisation, condensation and freezing
Different substances have different specific latent heats.
The specific latent heat of a given substance is different for boiling than it is for melting.

19. Latent heat of vaporisation

20. Evaporation in real life: Sweating

21. Evaporative Cooling
The high heat of vapourisation provides animals with an efficent cooling mechanism
As we sweat, body heat vapourises water and cools the body surface.
Evaporation of water from the leaves of plants cools their surfaces

22. Evaporation in real life: Transpiration

23. Evaporation in real life: The water cycle

24. Cohesion, adhesion,
surface tension
Cohesion, adhesion and surface tension are phenomena which reflect the polarity of the water molecules, and hydrogen bonds between water molecules adhesion

25. Let’s watch cohesion, adhesion and surface tension in action

26. 1. Filling up a penny!
You have a penny, a beaker of water and a dropper pipette.
How many drops of water can fit on to the top of the penny?

27. 2. The Magic pepper plate…

28. Cohesion
The attraction of like molecules to each other As a result of hydrogen bonding, water molecules form a dynamic structure with many breaking and forming bonds
Plays a key role in life processes, including transport of water and dissolved nutrients against gravity in plants Let’s watch!
Due to cohesion, water can act like a skin….the water molecules cling to each other rather than to the air molecules around them.
Drip water onto the penny. How does the water stick to the leaf and grow larger?

29. Adhesion
Attraction process between polar molecules of different substances (e.g. water/glass)
Again, due to the polarity of water and hydrogen bonding

31. Surface tension milk and water oh yeah, it's David.... Lotus Leaf
Surface tension is a property of the surface of a liquid that allows it to resist an external force
It is a measure of the force/unit length necessary to stretch or break the surface of a liquid
Related to cohesion
Water has a relatively high surface tension

32. Why does the water bead?
The water molecules beneath the surface are pulled in all directions. The molecules at the surface are pulled together and in. This creates a tighter arrangement of molecules at the surface and the round shape of a drop of water.

33. The Magic pepper plate
The charged end of a detergent molecule attracts water molecules at the surface in an outward direction. This disrupts the way the molecules normally attract at the surface and weakens the surface tension, causing the drop to collapse.

34. Special property 2: Ice is less dense than water
Water is less dense as a solid than a liquid
Usually substances shrink as they cool
Hydrogen bonding in ice causes water molecules to form a lattice, making it less dense than water
Canada Nature animation

35. What is density?
Density is the mass per unit volume. This means that the density of any solid, liquid or gas can be found by dividing its mass in kilograms by its volume in cubic metres.
Density (kg m-3) can be found using the equation:
The density of water is approximately 1000 kg m-3 and air is approximately 1.3 kg m-3

36. Phase change and density change
When most substances change from a solid state to a liquid state their volume does not change much. This is because the particles stay approximately the same distance apart. This means that the density of a substance, say iron, does not change by much when it melts.

37. When a liquid changes into a gas, the spacing between the particles increases by a factor of about ten. As such, because the volume of a substance is length × breadth × height, the volume will increase by a factor of 1000.
As a result, the density of a substance decreases by a factor of approximately 1000 when it changes from a liquid to a gas.

38. How do living things benefit from water expanding as it freezes?
If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid.
During the summer, only the upper few centimeters of the ocean would thaw.
Instead, the surface layer of ice insulates liquid water below, preventing it from freezing and allowing life to exist under the frozen surface.
Life under the ice