Properties and Roles of water Flashcards
structure of a molecule of water
a molecule of water contains 2 atoms of hydrogen chemically bonded to an atom of oxygen.
what type of bonds are the bonds between the hydrogen and oxygen atoms
-covalent bonds
what charges do the atoms in water molecules have
-oxygen atoms have a slightly negative charge
-hydrogen atoms have a slightly positive charge
why do scientists say that water is a polar molecule
-because the oxygen atoms in water have a slightly negative charge whereas the hydrogen atoms in water have a slightly positive charge, because of these charges, its a polar molecule.
what do the opposite charges mean for the water molecules
-the opposite charges means that the water molecules are attracted to each other
these forces of attraction are called hydrogen bonds’
hydrogen bonds are quite weak bonds however…
even a small volume of water contains a large number of hydrogen bonds.
so they have a large effect on the properties of water
in liquid water, how are the water molecules arranged
-as moving randomly however hydrogen bonds are still presenr
1) property of water
very high specifc heat capacity
means we have to put in or take out a large amount of energy to change the temperature of water.
when we heat water, the heat energy goes towards breaking or weakening the hydrogen bonds rather than increasing the kinetic energy of water molecules. because of this water acts as a buffer against rapid temperature changes.
the temperature of water tends to not change rapidly, so it can act as a habitat for aquatic organisms. aquatic organisms would not be able to function if temperature of water changed too rapidly such as on hot or cold days.
2) freezing
if temperatures are extremely cold water freezes and turns into ice
one key feature of ice is that is much less dense than liquid water so it floats. as well as being a habitat for a number of organisms, ice insulates the water beneath it, preventing it from freezing. this allows organisms to continue living in the water underneath the ice.
3) very high latent of heat of vaporisation
meaning it takes a large amount of heat energy to evaporate water
this allows organisms to cool themselves without losing a great deal of water.
e.g sweating. during sweating, heat energy is used to evaporate water from the surface of the skin. this transfer of heat energy allows organism to cool down
4) water is an excellent solvent
lots of substances can dissolve in water.
both eukaryotic and prokaryotic cells contain a large amount if dissolved substances for example the chemicals involved in metabollic reactions such as respiration as well as the enzymes needed to carry out these reactions.
bodies of water such as ponds and rivers contain large amounts of dissolved oxygen that is used by organisms living in the water to carry out respiration.
this makes water an excellent habitat for these organisms. because water is such a good solvent, it can be used to transport substances. a good example is the blood plasma. water is also used to transport substances in the xylem vessels of plants.
water in the xylem contains dissolved mineral ions such as the magnesium ion. magnesium ions pass into the plant roots from the soil. they are transported in the xylem from the roots to the leaves. once in the leaves, the magnesium ions are used to make chlorophyll for photosynthesis. because water is such a good solvent, it makes an excellent transport medium.
5) cohesion
water molecules tend to stick together, this is due to hydrogen bonds.
cohesion allows large columns of water to travel in xylem tubes. this makes water ideal as a transport medium in plants.
6) surface tension
cohesion also causes surface tension where water meets air.
surface tension allows surface of water to act as a habitat for insects such as pondskaters.
surface tension is caused by the water molecules being more attracted to each other than particles in the air. this causes them to stick together.
7) metabollic importance of water
water is a reactant in many different reactions includong hydrolysis reactions and photosynthesis
water is also produced in certain reactions including condensation reactions and aerobic respiration.
roles of cations :
role of calcium ions 2+
-muscle contraction
-nerve impulse transmission
