2.2 Water Flashcards
What are water molecules made of and what’s the bonding?
-Formed by covalent bonds between oxygen and 2 H atoms
Why are water molecules polar (refer to electrons and bonding)
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
What is cohesion?
Attraction between two of the same type of polar molecules
Why does cohesion happen? (Hint. H bonding)
Happens because water is polar and can form H bonds. H bonds are weak but multiple present so cohesive forces are strong
Adhesion
Attraction between two different types of polar molecules
How do organisms use cohesion?
- 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
Examples of adhesion
-Used as a transport medium for water in plants (Capillary action allows it to act against gravity)
3 thermal properties
- High specific heat capacity
- High latent heat of vaporization
- High boiling point
What is specific heat capacity?
Amount of heat required to raise 1g of substance by 1 degree C
Why does water have high specific heat capacity?
H bonds restrict motion of water molecules. Large amounts of energy are required to break H bonds
What is high latent heat of vaporization?
Heat required to change a liquid molecule to a vapor molecule
Why is water a solvent?
Dissolves anything with charged particles or polarity. Large qty. of water weakens intramolecular forces
How does dipolarity play a role in water’s solvent property?
Both charged regions of water surround atoms of opposing charge so both dissolve.
How do organisms use solvency of water?
- Cytoplasm is a complex mixture of dissolved substances and so can act as a medium for metabolic reactions
- Helps transport essentials molecules in bloodstream
Hydrophilic + examples
Anything that freely associates or dissolves in water. Eg. Polar, charged: glucose, Na/Cl ions
Hydrophobic + examples
Substances that dont freely associate or dissolve in water. Eg. Fats, oils, acetone
Solubility in blood: Glucose
Freely soluble. As it dissolves easily, it is carried in blood plasma
Solubility in blood: Amino acids
Soluble because they have positive/negative charges however solubility depends on R group. Can be carried in plasma
Solubility in blood: Cholesterol
Largely hydrophobic. OH group is not enough for it to dissolve
Solubility in blood: Fats
Non-polar and completely insoluble.
Solubility in blood: Oxygen
Non-polar but dissolves because of small size
Solubility in blood: NaCl
Ionic so completely soluble. Dissociates into Na and Cl ions and carried in blood plasma
What are cholesterols and fats carried in?
Lipoproteins as they are insoluble
What is oxygen carried in?
Carried in haemoglobin as oxygen becomes insoluble at increasing temp. so very little in plasma
What are lipoproteins?
- Phospholipid layer on the outside
- Tails of phospholipid are in contacts with fat
- Phospholipid heads face outside as they are hydrophilic
What happens if our body doesn’t cool?
Cells start to overheat which leads to denaturation of enzymes and destruction of cell. It could potentially/fatally harm our bodies
What property of water means its useful as coolant?
Thermal properties
How does body use thermal properties to cool body using sweat?
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
Compare thermal properties of water with methane
Methane is non-polar so it has lower specific heat capacity, lower latent heat of vaporization and lower melting/boiling point
Why is water able to remain a liquid at most temperatures as compared to methane as a gas?
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.
