Theme A: A1 Molecules - A1.1 Water

Question 1

solvent

Answer 1

the medium in which a substance dissolves

Question 2

non-polar covalent bonds

Answer 2

a bond formed when a pair of electrons are shared equally between 2 atoms
e.g. covalent bond between 2 carbon atoms or 2 hydrogen atoms

Question 3

polar covalent bonds

Answer 3

a bond formed when a pair of electrons are shared unequally between 2 atoms
e.g. covalent bond between oxygen and hydrogen in water molecules (water is therefore a polar molecule as the ends of the covalent bond between its oxygen hydrogen atoms have opposite charges)

Question 4

ephemeral

Answer 4

lasts only a short amount of time
e.g. in liquid water, the bond between water molecules is ephemeral because the molecules move around

Question 5

hydrogen bonding with water molecules

Answer 5

when the positive end of a hydrogen atom in a water molecule attracts the negative end of an oxygen atom in another

Question 6

cohesion

Answer 6

occurs when the same type of molecules are attracted to each other

Question 7

adhesion

Answer 7

attraction between 2 unlike molecules due to hydrogen bonding

Question 8

the process of transpiration

Answer 8

• The evaporation of water from open stomata, a part of the leaf of a plant, is called transpiration.
• The water is provided to the leaf by many xylem tubes.
• The transpiration of the water creates a low pressure area called tension. As the water molecules move to the low pressure area, this tension pulls other water molecules in the tube towards the leaf as they are all cohesive to each other and, thus, move up collectively.
• The waters adhesion to the sides of the xylem tube prevent the water column from falling back down when the water is not being “pulled up”.
• The water moving up is replaced by ground water entering the system.

Question 9

aqueous solution

Answer 9

any solution with water as the solvent
e.g. cytoplasm, water in xylem vessels, plasma in blood

Question 10

hydrophilic

Answer 10

any substance that dissolves in water, characterised as ‘soluble.’ (polar molecules are hydrophilic)
e.g. glucose, amino acids, starch

Question 11

hydrophobic

Answer 11

any substance that doesn’t easily dissolve in water, characterised as ‘insoluble.’ (non-polar molecules are hydrophobic)
e.g. steroid hormones like oestradiol and testosterone, hydrophobic sections in proteins, wax cuticle excreted from epidermal cells in leaves

Question 12

physical properties of water vs air

Answer 12

1) Buoyancy
Water: the buoyant force is equal to the weight of water displaced by the object. The buoyant force is upwards as there is more pressure below the object (water) than above (air).
Air: the buoyant force is equal to the weight of air displaced by the object. Insignificant buoyant force when the object is placed in the air.
2) Viscosity
Water: water’s resistances to an object moving through.
Air: air’s resistance to an object moving through. Since air is less dense, it has relatively less viscosity.
3) Thermal conductivity
Water: refers to the substances ability to transfer heat, where water has high thermal conductivity.
Air: air has a very low thermal conductivity in comparison.
4) Specific heat capacity
Water: water absorbs or gives off heat without changing much in temperature.
Air: the temperature of air changes easily and rapidly due to weather conditions.

Question 13

examples that apply the properties of water.

Answer 13

Black throated loon:

Ringed seal:

Question 14

the 2 forms of water

Answer 14

1) Typical water: contains ordinary hydrogen atoms without any neutrons
2) Heavy water: contains hydrogen atoms with a neutron. This hydrogen is called a deuterium
All bodies of water contain a mix of these, though typical water is more common. The ratio of hydrogen to deuterium in oceans in very similar to the ratio in asteroids.

Question 15

Goldilocks zone

Answer 15

the position of the earth in relation to the sun is called the habitable zone or Goldilocks zone. (edit to apply to all planets)

Question 16

necessary conditions for a planet to be in a Goldilocks zone

Answer 16

1) in an orbit that allows water retention to occur
2) suitable temperature for liquid water to exist
3) sufficient gravity for retaining water
4) suitable size for gravitational pull to keep water on the planet and just under its surface
5) has an atmosphere and magnetic field to protect from ionising radiation from its sun

Question 17

capillary action

Answer 17

The ability of water to flow in narrow spaces without the assistance of external forces, such as gravity. This occurs due to the combination of cohesion (water molecules sticking to each other) and adhesion (water molecules sticking to surfaces like plant cell walls). examples: capillary action in soil and cell wall