IB - Topic 2.2 - Water

Terms in this set (28)

polar
unequal sharing of electrons in covalently bonded molecules that causes a slight opposite charge
hydrogen bond
attractive force that forms when a hydrogen atom in one polar molecule is attracted to a slightly negative atom of another polar covalent molecule
dipolarity
polar molecules have a slight positive and slight negative charge
cohesion
binding together of 2 molecules of the same type
adhesion
hydrogen bonds can form between water and other polar molecules
thermal properties of water
high specific heat capacity
high latent heat of vaporization
high boiling point
high specific heat capacity
the amount of energy needed to raise the temperature of water is large / to cool down, water must lose relatively large amounts of energy because hydrogen bonds have to be broken / formed (good for aquatic organisms)
high latent heat of vaporization
considerable amounts of heat are needed to evaporate water because hydrogen bonds have to be broken
high boiling point
the highest temperature water can reach in a liquid state is relatively high because hydrogen bonds have to be broken
solvent properties of water
the polar nature of water means that it forms shells around other polar and charged molecules, preventing them from clumping together and keeping them in solution
hydrophilic
substances that are chemically attracted to water, that dissolve in water including polar molecules such as glucose and cations/anions
hydrophobic
non polar substances that do not have a charge tend to be insoluble in water.
All lipids are hydrophobic, including fats and oils
methane
non-polar covalent molecule
water
polar covalent molecule
Why are some insects able to walk on water?
Surface tension, due to hydrogen bonding, creates a thin film on the surface of water that gives enough resistance for light insects to walk on
Why do lakes freeze from top down?
Hydrogen bonds keep water molecules further apart in frozen molecule than in liquid water. The further apart those molecules are, the less dense that solid is.
water molecules
bent, 104.5 degree angles, oxygen is partially negative due to the polar covalent bond.
cohesive properties example
This is useful for plants as water can be sucked through the xylem at low pressure because the molecules 'pull' each other
adhesive properties example
This also aids in the transport of water in plants as the water adheres to the cellulose found in the cell wall of the plant cells.
Solvent properties
Water forms 'shells' around charged and polar molecules, which dissolves them and prevents them from clumping together.
Thermal properties ex: Sweating
When sweat is released by the sweat glands, it spreads across the skin and absorbs heat from the surrounding tissues When the water evaporates, it carries this heat away from the body, cooling it overall.

Sweat secretion is controlled by the hypothalamus in the brain, which has thermoreceptors that monitor blood temperature.
Water vs. Methane
Methane does not form hydrogen bonds and is nonpolar
Methane has a lower specific heat, which means it takes less energy to heat. This results from the lack of H-bonds which prevent vibration.
Methane has lower heat of vaporization
Methane has lower melting and boiling points
Mode of transport of glucose
polar molecule, soluble in water, dissolves in the blood plasma
Mode of transport of amino acids
all soluble enough to dissolve and be transported.

AA's have both negative and positive charges and so are soluble in water. However, the degree of their solubility depends on the R group, some of which are hydrophilic while others are hydrophobic.
Mode of transport of fats
Fats are large, nonpolar and are insoluble in water.
They are carried through the in lipoprotein complexes which are groups of molecules with a single layer of phospholipids on the outside. The hydrophilic heads of the phospholipids face outwards while the hydrophobic tails face inwards towards the contents of the lipoprotein.
Mode of transport of cholesterol
Mostly hydrophobic except for a small region at one end. This however, is not enough to make the molecule dissolve in water.

Instead it is transported with the fats inside the lipoprotein complexes.

They are embedded in the single layer of phospholipids with the small hydrophilic region facing outwards.
Mode of transport of sodium chloride
ionic compound, soluble in water. Forms Na+ and Cl- and this is carried through the blood plasma
Mode of transport of oxygen
O2 is a nonpolar molecule but is able to slightly dissolve due to being small but the saturation level is too low to meet the needs of aerobic cell respiration. To circumvent this, hemoglobin is used which has binding sites for oxygen. This greatly increases the capacity of blood for oxygen transport.
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