2.2 (Water)

Question 1

What is the essential idea?

Answer 1

Water is the medium of life

Question 2

Discuss the structure of a water molecule.

Answer 2

• Two hydrogen atoms, covalently bound to an oxygen atom
• Electrons are shared but not equally
• Oxygen atoms have 8 protons and hydrogen atoms have 1
• This means oxygen atoms attract electrons more strongly
• Oxygen end of the molecule becomes slightly negative and the hydrogen end becomes slightly positive

Question 3

Discuss covalent bonds.

Answer 3

• Covalently bonded molecules that have a slight potential charge are polar
• The slightly charged regions of the water molecule can attract other polar compounds
• Water molecules can associate via weak hydrogen bonds
• Hydrogen bonds are transitory in nature – they constantly form, break and re-form

Question 4

Discuss cohesion.

Answer 4

• Results due to polarity and ability to form hydrogen bonds
• Hydrogen bond are weak but the large number gives cohesive forces strength
• Tend to stick to one another
• Water droplets form because the cohesive forces are trying to pull the water into the smallest possible volume, a sphere

Question 5

Discuss adhesion.

Answer 5

• Water molecules stick to non-water polar surfaces
• Capillary action is caused by the combination of adhesive forces causing water to bond to a surface
• The sides of a xylem vessel and the cohesive forces bonding water molecules together. Capillary action is helpful in the movement of water during transpiration and also when you drink using a straw.

Question 6

Discuss solvent properties.

Answer 6

• Water can dissolve many organic and inorganic substances that have charged or polar regions.
• The polar attraction of large quantities of water molecules can interrupt intramolecular forces (such as ionic bonds) and resulting in the dissociation of the atoms
• Positive atoms, end up being surrounded by the negative oxygen regions of water molecules and the Cl- being surrounded by the positive hydrogen region of water molecules

Question 7

Discuss thermal properties.

Answer 7

• High specific heat capacity
• High heat of vaporisation and fusion
• Temperature of water remains relatively stable

Question 8

Discuss water as a coolant.

Answer 8

• Water removes a lot of energy when it evaporates

- Felt as a cooling sensation; excess heat is removed from the body, skin and blood vessels are cooled

Question 9

Define hydrophilic.

Answer 9

Substances chemically attracted to water (all substances which dissolve in water are hydrophilic)

Question 10

Define hydrophobic.

Answer 10

Substances repelled by or insoluble in water (nonpolar)

Question 11

Discuss glucose in relation to water.

Answer 11

Freely soluble and carried by the blood plasma

Question 12

Discuss amino acids in relation to water.

Answer 12

Soluble in water, but R group varies, from polar, non-polar or charged. R group determines degree of solubility. Carried by blood plasma

Question 13

Discuss oxygen in relation to water.

Answer 13

Non-polar, only just soluble in water. As temperature increases, solubility decreases. Carried in red blood cells by hemoglobin

Question 14

Discuss fats in relation to water.

Answer 14

Large, non-polar molecules, insoluble in water. Carried in blood inside lipoprotein complexes

Question 15

Discuss cholesterol in relation to water.

Answer 15

Molecules are hydrophobic, apart
from a small hydrophilic region at one end. Not enough to make cholesterol dissolve in water. Carried in blood in lipoprotein complexes

Question 16

Discuss lipoprotein complexes in relation to water.

Answer 16

• Outer layer consists of single layer of phospholipid molecules
  hydrophilic phosphate heads of the phospholipids face outwards and are in contact with water
• Hydrophobic hydrocarbon tails face inwards and are in contact with the fats
  cholesterol molecules are positioned in the phospholipid monolayer - hydrophilic region facing outwards
• Proteins are also embedded in the phospholipid layer

Question 17

Discuss sodium chloride in relation to water.

Answer 17

Ionic compound, freely soluble in water, dissolving to form sodium ions and chloride ions. Carried in blood plasma