topic 2.2- water Flashcards
what type of molecule is water?
water is a polar molecule
what is a polar molecule?
a molecule with an uneven distribution of charge
what is a hydrogen bond?
a weak interaction, or intermolecular force, that forms when a hydrogen atom in one polar molecule is attracted to a slightly negative atom of another polar covalent molecule.
state the 4 main properties of water
- adhesive properties
- cohesive properties
- thermal properties (high specific heat capacity/high latent heat of vaporisation)
- solvent properties
define cohesion
binding together of two of the same type of molecules
why are water molecules cohesive?
- polarity
- hydrogen bonds form
- stick together
give two example of a real-life use of cohesion.
water transport in plants, transpiration:
- water sucked/pulled up through xylem vessels at a low pressure.
surface tension:
- allows insects to move on surface
why are water molecules adhesive?
- polarity
- hydrogen bonds form
- stick with other molecules
define adhesion
the binding of water molecules to other polar molecules
give a real-life example of adhesion
- in leaves, water adheres to cellulose molecules in cell walls.
- if water evaporates from the cell wall and is lost from the leaf, adhesive forces cause water to be drawn out of nearest xylem vessel
- this keeps walls moist to absorb CO2 for photosynthesis
define specific heat capacity
amount of energy needed to raise the temperature of water by 1’C
explain water’s high specific heat capacity
energy needed due to intermolecular H-bonds.
give a real-life example of the uses of water’s high specific heat capacity
water is a thermally table habitat for aquatic organisms as its temperature remains relatively stable in comparison to air/land.
define latent heat of vaporisation
the heat needed to cause a change of state from a liquid to a gas in water (ie for a water molecule to become a vapour molecule)
explain water’s high latent heat of vaporisation
hydrogen bonds need to be broken in order for water to evaporate
explain a real-life use of water’s high latent heat of vaporisation
sweat:
- sweat secreted by glands
- heat needed for the evaporation of water in swear is taken from tissues of the skin, reducing their temperature
- blood therefore cooled
why does water have such solvent properties?
- polarity of the water means allows other charged particles to dissolve
why does liquid water have a high density?
in liquid state, inter molecular hydrogen bonds hold water molecules closer together.
what uses does water’s high density have?
it has a support function and aids buoyancy
why is water less dense as a solid?
as water solidifies, the intermolecular hydrogen bonds help to create a regular formation
why is water being less dense as a solid significant?
floats on liquid water:
- provides a habitat for arctic/antarctic animals
- insulates water below during winter
define hydrophobic molecules
molecules that are insoluble in water but dissolve in other solvents (eg propanone)- this happens for non-polar molecules (no negative/positive charges).
give an example of hydrophobic molecules
all lipids, fats and oils
define hydrophilic substances
substances that are chemically attracted to water (any substance that dissolves in water)
