2.2 Water Flashcards
Describe the cause and effect of the polar nature of water
- Water consists of two hydrogen atoms covalently bonded to an oxygen atom.
- Oxygen is more electronegative than hydrogen, so it attracts the electrons more strongly, causing an unequal distribution of electrons in the molecule. A permanent dipole is formed (water molecules are dipolar).
- The is a slight charge difference in the molecule: oxygen slightly negative, hydrogen slightly positive
Describe where and how water is able to form hydrogen bonds
- The partially positive hydrogen of one water molecule forms a hydrogen bond with the partially negative oxygen of another molecule, and vice versa - allows water molecules to stick together.
- hydrogen bond are also formed with N and F
Define cohesion and explain it as a property of water,
Cohesion - binding between molecules of the same type
Water molecules are cohesive - they are held together by hydrogen bonds.
Define adhesion and explain it as a property of water
Adhesion - attraction between molecules of different substances.
Water molecules are adhesive - they attach to other substances by hydrogen bonding (other polar molecules) or attraction to ionic charge (ions)
Outline an example of the cohesive property of water being of benefit to life
- Creates surface tension - provides a habitat for insects as they are able to stay on surface of water.
- Transport of water in plants - water molecules stick together, forming chains. This allows them to move through the xylem despite the low pressure.
Outline an example of the adhesive property of water being of benefit to life
Capillary action in plants: water sticks to sides of xylem (cellulose in cell walls) through adhesion. Adhesive forces then draw water from the xylem to the leaves (attraction to charged/polar surfaces allows water to flow in opposition of gravitational forces)
Explain three thermal properties of water that are useful to living organisms
(Outline a benefit to life of water’s high specific heat capacity)
(Outline a benefit to life of water’s high latent heat of vaporization)
(Outline a benefit to life of water’s high boiling point)
- High specific heat capacity - large amount of energy needed to raise temperature in water (and change its state). This is because hydrogen bonds restrict the motion of water, and need to be broken, which requires large amount of energy. The stability of water temperature stabilizes climate and provides thermally table habitats.
- High latent heat of vaporization - large amounts of energy are needed for water to become a vapour. Hydrogen bond need to be broken before it can evaporate. Creates evaporative cooling: prevent overheating, regulates temperature of water in bodies, decreases environmental temperatures.
- High boiling point - helps keep internal and external condition constant.
Overall creates a stable environment for living organisms.
Use of water as a coolant is sweat
Water requires a lot of energy to evaporate. When warm, this energy comes from surface of the skin. Due to high latent of vaporization, a lot of thermal is required before the sweat can evaporate from the skin’s surface (after being carried there by narrow ducts). Thus the heat of the tissues in the skin is used, reducing body temperature
Explain why water is such a good solvent.
Water is the universal solvent - can dissolve large variety of matter. It dissolves any substances containing ions (charged particles) or polar molecules, this is because water readily form hydrogen bonds them. The charged regions of water surround atoms of opposite charge, forming “shells” around them (keeping them from clumping together)
Water soluble substances (transported freely in blood plasma)
- Sodium chloride: ionic compound, dissolved in water to from positive and negative ions.
- Oxygen: non-polar, but can dissolve in low amount due to small size. Carried by hemoglobin in red blood cells. (increase in water temperature = decrease in solubility of oxygen
