A1.1 Water

Question 1

Water as the medium for life

Answer 1

Life on earth began in the ocean (+ vesicles)

Substances dissolved in water -> chem. reactions between solutes.

Question 2

Answer 2

Molecules bent rather than linear -> Hydrogen on the same side and form one pole. H2O is dipolar.

Question 3

Electronegativity

Answer 3

A chemical property that describes the tendency of an atom to attract electrons toward itself.

Question 4

Electronegativity of H2O

Answer 4

O pulls H electrons towards it. O = δ- (partial neg.) and H = δ+

Question 5

Hydrogen bonding

Answer 5

Electrostatic attraction between H atom in a polar molecule and a small electroneg. atom (O, N, or F) in another.

Question 6

Cohesion

Answer 6

Alike molecules sticking togehter due to intermolecular forces of attraction (e.g. hydrogen bonds).

Question 7

Conduction of water in the xylem

Answer 7

Cohesion allows transport of water w/ help of tension.

Roots = soil particles + water attract
Leaves = water evap. atm. and attraction water molecules + cell wall of leaf cells.

Question 8

Why does water move upwards in the xylem?

Answer 8

Pulling forces in the leaves > forces in the roots.

Question 9

Surface tension (water)

Answer 9

An elastic-like membrane that forms because water molecules are more attracted to each other in hydrogen bonding than to air particles.

Question 10

Why does surface tension make it possible for objects to float?

Answer 10

Cohesion between water molecules > attraction between water and floating object. (some animals use this to inhabit water surfaces)

Object break through -> many hydrogen bonds must be broken simultaneously.

Question 11

Adhesion

Answer 11

When hydrogen bonds form between water and the surface of a solid composed of polar molecules. -> Water sticks to the surface.

Question 12

Capillary action

Answer 12

When liquid flows through narrow spaces without external forces, rather, the liquid’s movement is aided by intermolecular forces between the liquid and solid surface(s).

Occurs: adhesion to the walls > cohesive forces liquid molecules.

Question 13

Capillary action glass tube

Answer 13

As air is replaced by water, many H bonds form between glass and water, releasing energy.

Question 14

Why can porous solides such as paper exert strong suction forces through adhesion?

Answer 14

They have a large amount of surface area to attract water.

Question 15

How water can rise up from an underground source, even though gravity tends to pull it down?

Answer 15

Water is attracted to many chemical substances in soil. If soil is porous, water is drawn by capillary action through dry soil, wetting it.

Question 16

Capillary action usefulness in leaves

Answer 16

Water evaporates from cell walls -> lost to atm. -> adhesive forces draw water out nearest xylem vessel.

This keeps the walls moist -> can absorb CO2 needed for photosynthesis. Also generates low pressures that draw water up xylem vessels.

Question 17

Capillary action usefulness refill xylem

Answer 17

Xylem vessel becomes air-filled -> adhesion between water + wall of vessel helps vessel to refill with water.

Question 18

Solvent

Answer 18

Substance capable of dissolving other substances.

Question 19

Solute

Answer 19

A dissolved substance (present in a smaller amount than the solvent in a solution).

Question 20

Solution

Answer 20

A mixture of one or more solutes dissolved in a solvent.

Question 21

Water important solvent properties

Answer 21

H2O polar -> forms shells around charged + polar molecules. Prevents clumping so they remain in solution.

Partial neg. attracted to cations + partial pos. attracted to anions -> both dissolve.

H2O forms H-bonds w/ polar molecules.

Question 22

Hydrophilic

Answer 22

Substances chemically attracted to water. All dissolve in water (polar or charged).

Substances that water adheres to but does not dissolve (e.g. cellulose) also hydrophilic.

Question 23

Hydrophobic

Answer 23

Not repelled by water but not attracted -> more attracted to other hydrophobic subst.

Non-polar + not charged. -> Insoluble in water but may dissolve in other solvents.

All lipids are hydrophobic.

Question 24

Water as a medium for metabolism

Answer 24

Cytoplasm = is an aqueous solution and solvent is water. Solutes move around + interact.

Question 25

Metabolism in the cytoplasm

Answer 25

Diff. chem. reactions catalysed in cytoplasm collectively known as metabolism.

Without water, the components of reactions can’t come together on enzymes active sites.

Question 26

Transport in plants

Answer 26

Substances transported as an aqueous solution.

Minerals ions transported in xylem sap. Sucrose + products of photosyn. in phloem sap.

Question 27

Transport in blood - ions

Answer 27

NaCl = soluble -> dissolved to Na+ and Cl-

Question 28

Transport in blood - amino acids

Answer 28

Soluble: have neg. + pos. charges -> solubility varies depending on variable molecule part, phillic or phobic.

Question 29

Transport in blood - glucose

Answer 29

Polar molecule -> soluble.

Question 30

Transport in blood - oxygen

Answer 30

Non-polar (dioxygen) -> small size = dissolve water sparingly -> saturates H2O at low conc.

Temp. rises -> solubility decreases.

Haemoglobin binding sites for O increases capacity of O transport around body for aerobic cell resp.

Question 31

Transport in blood - fat molecules

Answer 31

Non-polar -> insoluble -> coalesce = form large droplets in blood.

Small drops coated single layer phospholip. -> prevent water contact -> small drops suspended while transported.

Question 32

Buoyancy

Answer 32

Object immersed in fluid -> fluid exerts upward force on object (= weight fluid displaced).

Object density < fluid density THEN force acting on object > force due to gravity. So the object floats.

Question 33

How does buoyancy make water habitable?

Answer 33

Living organisms have overall denisty close to water -> easier to use as habitat than air as not much energy needed to float and more needed energy to stay airborne.

Question 34

Viscosity

Answer 34

A fluids resistance to flow due to its internal friction (H-bonds) when one part of fluid moves relative to another.

Question 35

Viscosity complications habitat

Answer 35

Solutes increase viscosity -> seawater higher viscosity due to dissolved salts -> more resistance is met for an animal trying to move through water.

Question 36

Thermal conductivity

Answer 36

Rate at which heat passes through a material.

Water has relatively high TC -> useful when there is a need to absorb and transfer heat.

Question 37

Specific heat capacity

Answer 37

The heat required to raise the temperature of 1g of a material by 1°C.

Water relatively high HC -> a lot of energy needed to break H-bonds -> stable temps.

Question 38

Extraplanetary origin of water on
Earth

Answer 38

Likely asteroids that collided w/ Earth early in its history contained more water.

Question 39

Water was retained on Earth after its delivery by asteroids, two factors are significant:

Answer 39

Distance to Sun = sunlight never raises temps for boil. Liquid water retained easier than vapour bc cohesion from H-bonding.

Earth size = relatively strong gravity -> holds oceans tightly to surface + gases in the atm.

Question 40

Goldilocks zone

Answer 40

Habitable zone around a star.
Planet is too close = water vaporize.
Too far = water freezes.

Depends: star size + amount energy emits. Planet size determine gravity strength + atm pressure.