2.2 Water

Question 1

What are water molecules made of and what’s the bonding?

Answer 1

-Formed by covalent bonds between oxygen and 2 H atoms

Question 2

Why are water molecules polar (refer to electrons and bonding)

Answer 2

Covalent bond is polar because nucleus of oxygen attracts shared electrons more than nuclei of H atoms. Therefore oxygen has a partial negative charge and hydrogen, a partial positive

Question 3

What is cohesion?

Answer 3

Attraction between two of the same type of polar molecules

Question 4

Why does cohesion happen? (Hint. H bonding)

Answer 4

Happens because water is polar and can form H bonds. H bonds are weak but multiple present so cohesive forces are strong

Question 5

Adhesion

Answer 5

Attraction between two different types of polar molecules

Question 6

How do organisms use cohesion?

Answer 6

• Plants use it as transport medium for water at low pressures (water can be pulled up)
• Surface tension=increased density so small organisms can float on water

Question 7

Examples of adhesion

Answer 7

-Used as a transport medium for water in plants (Capillary action allows it to act against gravity)

Question 8

3 thermal properties

Answer 8

1. High specific heat capacity
2. High latent heat of vaporization
3. High boiling point

Question 9

What is specific heat capacity?

Answer 9

Amount of heat required to raise 1g of substance by 1 degree C

Question 10

Why does water have high specific heat capacity?

Answer 10

H bonds restrict motion of water molecules. Large amounts of energy are required to break H bonds

Question 11

What is high latent heat of vaporization?

Answer 11

Heat required to change a liquid molecule to a vapor molecule

Question 12

Why is water a solvent?

Answer 12

Dissolves anything with charged particles or polarity. Large qty. of water weakens intramolecular forces

Question 13

How does dipolarity play a role in water’s solvent property?

Answer 13

Both charged regions of water surround atoms of opposing charge so both dissolve.

Question 14

How do organisms use solvency of water?

Answer 14

• Cytoplasm is a complex mixture of dissolved substances and so can act as a medium for metabolic reactions
• Helps transport essentials molecules in bloodstream

Question 15

Hydrophilic + examples

Answer 15

Anything that freely associates or dissolves in water. Eg. Polar, charged: glucose, Na/Cl ions

Question 16

Hydrophobic + examples

Answer 16

Substances that dont freely associate or dissolve in water. Eg. Fats, oils, acetone

Question 17

Solubility in blood: Glucose

Answer 17

Freely soluble. As it dissolves easily, it is carried in blood plasma

Question 18

Solubility in blood: Amino acids

Answer 18

Soluble because they have positive/negative charges however solubility depends on R group. Can be carried in plasma

Question 19

Solubility in blood: Cholesterol

Answer 19

Largely hydrophobic. OH group is not enough for it to dissolve

Question 20

Solubility in blood: Fats

Answer 20

Non-polar and completely insoluble.

Question 21

Solubility in blood: Oxygen

Answer 21

Non-polar but dissolves because of small size

Question 22

Solubility in blood: NaCl

Answer 22

Ionic so completely soluble. Dissociates into Na and Cl ions and carried in blood plasma

Question 23

What are cholesterols and fats carried in?

Answer 23

Lipoproteins as they are insoluble

Question 24

What is oxygen carried in?

Answer 24

Carried in haemoglobin as oxygen becomes insoluble at increasing temp. so very little in plasma

Question 25

What are lipoproteins?

Answer 25

• Phospholipid layer on the outside
• Tails of phospholipid are in contacts with fat
• Phospholipid heads face outside as they are hydrophilic

Question 26

What happens if our body doesn’t cool?

Answer 26

Cells start to overheat which leads to denaturation of enzymes and destruction of cell. It could potentially/fatally harm our bodies

Question 27

What property of water means its useful as coolant?

Answer 27

Thermal properties

Question 28

How does body use thermal properties to cool body using sweat?

Answer 28

Water needs to absorb large amounts of energy before it evaporates. Absorption of energy at skin surface allows tissue to cool and hence the blood flow to cool as water and heat escape

Question 29

Compare thermal properties of water with methane

Answer 29

Methane is non-polar so it has lower specific heat capacity, lower latent heat of vaporization and lower melting/boiling point

Question 30

Why is water able to remain a liquid at most temperatures as compared to methane as a gas?

Answer 30

Water can form large number of H bonds with other H2O molecules and so it has higher boiling points. As temps. on Earth are often between 0C to 100C, it’s mostly found in liquid form.