Topic 1.7 - Water Flashcards
What is electronegativity?
The tendency of an atom to attract a bonding pair of electrons for covalent bonding
What are polar molecules?
Where a neutral molecule has a positive area at one end and a negative area at the other end
Explain why water is a polar molecule
Oxygen is more electronegative in the covalent bond between oxygen and hydrogen, creating a partial positive and negative charge
What are dipoles?
The two ends of a polar molecule
What is a hydrogen bond?
Electrostatic attraction between the partial positive charge near the hydrogen atoms and the partial negative charge near the oxygen
How strong are hydrogen bonds in comparison to covalent bonds?
Hydrogens are about 5% as strong as covalent bonds
Why does water stay liquid over a wide range of temperatures?
Many hydrogen bonds mean that water is very strong so hella energy needed to break these bonds and get water to change state
What is cohesion?
The force by which hydrogen bonds hold polar molecules together
Why do water molecules have strong cohesive forces?
Because hydrogen bonds allow them to ‘stick together’
What is surface tension?
The tendency of a liquid to resist rupture when placed under tension or stress
Why does water have surface tension?
Water molecules at the top are exposed to air on one side so they have fewer neighbouring molecules so they’ll form stronger hydrogen bonds with the few neighbouring molecules they have
What is adhesion?
The attraction of molecules of one kind for molecules of a different kind
What is capillary action?
The upward motion of water against gravity
What two properties of water allow for capillary action?
Cohesion and adhesion
How does capillary action take place?
Water molecules are more strongly attracted to the glass than they are to other water molecules (because glass molecules are even more polar than water molecules).
What is a solvent?
A substance which is able to dissolve other substances
Why is water a good solvent?
Water is polar
Surrounds charged particles and pulls them apart
Why is water as a liquid being incompressible useful?
Can be used in hydraulic systems and in hydrostatic skeletons of animals like jellyfish
Why can ice float on water?
Because it’s less dense than water
Why is ice less dense than water?
When water freezes molecules form a crystalline structure maintained by hydrogen bonding and the orientation of these bonds causes molecules to push further apart
At what temperature does water reach its maximum density?
4 degrees Celcius
Why do mammals cool when sweat evaporates?
Because hella energy is required to break the hydrogen bonds to turn the water into a vapour so the temperature drops as energy is taken away
Why is the temperature slow to change in large bodies of water?
Because water has a high specific heat capacity so lots of energy is required to raise the temperature by a little bit due to hydrogen bonds
What is the specific heat capacity of water?
4.2J/g/C
Why does hydrophilic mean?
Substances that will mix with water
What does hydrophobic mean?
Substances that will not mix with water
Describe the structure of a water molecule and its bonding
Two hydrogen atoms covalently bonded to an oxygen atom
Name properties of water
Good solvent High specific heat capacity Surface tension Incompressible Max density at 4 degrees
What is specific heat capacity?
The energy needed to raise the temperature of 1kg of a substance by 1 degree
What is the advantage of water having a high specific heat capacity?
The temp of aquatic environments stays stable over a wide range of temperatures because lots of energy is needed to raise the temp
Water is incompressible - how can this be used in industry?
Used in hydraulic systems
How can water be used in plants?
Photosynthesis
Transport
Structural support
Thermoregulation
Give two properties of water which are needed in the cytoplasm of cells
Water is polar so it’s a good solvent and reactions happen better in solution
Reactive so it takes place in hydrolysis
What is the cause of many of water’s properties?
Hydrogen bonding bc water is polar
