3.2 - Water Flashcards
Describe the polarity of water.
The 3 elements in water are covalently bonded
- Oxygen is electronegative, the electrons in the bond are attracted towards the oxygen giving it a partially negative charge
- Subsequently the hydrogen acquires a slightly positive charge
What is a hydrogen bond?
A bond between water molecules which exists between the partially negative oxygen of one molecule and the partially positive hydrogen of another.
Weaker than covalent bonds
What is the boiling point of water like and why?
Unusually high due to the strong hydrogen bonds which require lots of energy to break them apart.
This gives it a high specific heat capacity and high latent heat of vapourisation.
Why is ice less dense than water?
Below 4 degrees Celsius the hydrogen bonds fix positions further apart than in water, making the molecules to unit volume ratio less, making it more dense.
They arrange in a tetrahedral structure, which is rigid and open.
It is a good habitat for seals as it floats and gives them somewhere to linger.
- Also acts as insulator for organisms living below the ice.
What are the cohesive properties of water?
- Water moves as one mass due to the attraction between the molecules (called cohesion)
- This helps plants to draw up water through the root as the water moves as one body.
What is surface tension?
Since there are fewer water molecules to come into contact with at surface (due to air being just above it), the water molecules form stronger bonds at surface.
- This keeps boats afloat, allows some insects to ‘skate’ or walk on water.
- Referred to as skin of surface tension.
What are the adhesive properties of water?
Water is attracted to different surfaces, for example when you wash your hands the water doesn’t run straight off.
How does water act as a solvent?
The polarity of water allows it to form hydrogen bonds with other charged or polar molecules.
Molecules that link to water in this way are water soluble.
- Solutes in an organisms cytosol can be dissolved into and out of cells (the cytosol in eukaryotes are mainly water).
- Acts as a medium for chemical reactions.
How is a water an effective transport medium?
Adhesion and cohesion allows for capillary action.
CAPILLARY ACTION
- Water can rise up through narrow tubes against the force of gravity (like in plants)
- Also taking polar and/or charged molecules with them to TRANSPORT them.
How does water act as a coolant?
Water is stable and does not change temperature easily due to the amount of energy required to manipulate the hydrogen bonds.
- It buffers temperature changes during chemical reactions.
Why is water maintaining temperature during chemical reactions important?
Enzymes have a narrow temperature operating window.
