3.2 : Water Flashcards
How does water bond? Why is it polar?
The oxygen and hydrogen atoms are covalently bonded. However the oxygen has a greater share of electrons in the O-H bond, and so it is slightly negative. This means that the oxygen has a smaller share of electrons, and so it is slightly positive.
Therefore , water is polar as it has negative regions and positive regions.
What are hydrogen bonds?
The positive regions and negative regions of a polar substance are attracted to each other and form hydrogen bonds. These jare relatively weak interactions, which break and reform between the constantly moving water molecules.
What are the characteristics of water?
High boiling point Ice less dense than water so it floats Cohesive Adhesive Stable temperature
Why does water have a high boiling point?
Water is liquid at room temperature. This is due to the hydrogen bonding. It takes a lot of energy to over come these bonds, change the temperature and make the water evaporate.
Why is ice less dense than water and able to float?
When water freezes to ice it becomes less dense. As water is cooled below 4°C the hydrogen bonds fix the position of the polar molecules slightly further apart than the average distance in the liquid state. This results in a giant, rigid but open structure, with every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms.
Why is water cohesive and adhesive?
Cohesive : It moves as one mass because the molecules are attracted to each other. This is why transpiration streams are able to form.
Adhesive : the water molecules are attracted to other molecules. This is why something’s can get wet, and water doesn’t run straight off.
What are the uses of water?
Solvent
Coolant
Transport medium
Habitat
How is water a solvent?
Many solutes in an organism can be dissolved in water because it is polar. The cytosol of prokaryotes and eukaryotes is mainly water. Water acts as a medium for chemical reactions and also helps transport dissolved compounds into and out of cells.
Why is water a good transport medium in living things?
Cohesion of water means that when it is transported through the body, molecules will stick together. Adhesion occurs between water molecules and other polar molecules and surfaces.
The result of this is water exhibiting capillary action. This is the process by which water can rise up a narrow tube against the force of gravity.
How is water a coolant?
It helps to buffer temperature changes during chemical reactions in prokaryotic and eukaryotic cells because of the large amounts of energy required to overcome the hydrogen bonding.
This is important as enzymes are often only active in a narrow temperature range.
Why is water a good habitat for aquatic organisms?
Water is stable - it does not change temperature of become a gas easily, so it provides a constant environment.
As ice floats, it forms on the surface of ponds and lakes, rather than from the bottom up. This forms an insulating layer above the water below. Aquatic organisms would not be able to survive freezing temperatures if their entire habitat froze solid.
Some organisms also inhabit the surface of water. Surface tension is strong enough to support small insects such as pond skaters.
Why does water have surface tension?
Water molecules are more strongly cohesive to each other than they are to air which results in water having a ‘skin’ of surface tension.
