Water Flashcards
Describe the term polarity & explain why Water is polar and dipolar
A molecule having a positive and negative charge
Why is Water polar?
Water molecules are polar because the hydrogen molecule has a positive charge and the 2 oxygen molecules have a negative charge
Why is Water dipolar?
Water is a dipolar molecule (having dipolarity) because it has two poles and each atom has a dipole or partial charge.
Define a Coolant
A substance that removes or transfers heat.
(e.g sweat is a coolant. evaporation of water from sweat for example, breaks the hydrogen bonds between water molecules in the sweat, thus, removing heat from the body.)
Relative to methane water is higher in all these areas.
Thus, State the melting point of water, the specific heat capacity of water, the latent heat of evaporation of water and the boiling point of water
1) The melting point of water (0°C)
hydrogen bonds restrict the movement of water molecules and heat is needed to overcome this
2) The specific heat capacity of water (4.2j per °C)
illustrates how hydrogen bonds restrict movement so more energy is stored by moving molecules of water than methane
3) The latent heat of evaporation of water (2257 J/g)
illustrates how much heat energy is needed to break hydrogen bonds and allow a water molecule to evaporate.
4) the boiling point of water (100°C)
heat energy is needed to break hydrogen bonds and allow water to change
from a liquid to a gas.
What substances are hydrophilic? and What substances are hydrophobic?
Hydrophilic (attracted to water)
1) Ionic compounds as well as substances with polar molecules
Hydrophobic (afraid of water)
2) substances insoluble to water (e.g non polar molecules such as fats and oils)
What does the mode of blood transportation depend on?
Depends on a substance’s solubility in water. Water-soluble substances will usually be able to travel freely in the blood plasma, whereas water-insoluble substances cannot
Give examples of Water Soluble Substances with regards to blood transport
Water Soluble Substances
1) Sodium chloride (NaCl) is an ionic compound and its components (Na+ and Cl–) may be freely transported within the blood
2) Oxygen is soluble in water but in low amounts – most oxygen is transported by haemoglobin within red blood cells
3) Glucose contains many hydroxyl groups (–OH) which may associate with water and thus can freely travel within the blood
4) Amino acids will be transported in the blood in an ionized state (either the amine and/or carboxyl groups may be charged)
Give examples of Water insoluble Substances with regards to blood transport
Water Insoluble Substances
1) Lipids (fats and cholesterol) are non-polar and hydrophobic and hence will not dissolve in water
2) They form complexes with proteins (lipoproteins) in order to move through the bloodstream
3) Hydrophilic portions of proteins, cholesterol and phospholipids will face outwards and shield internal hydrophobic components
State the 3 properties of water
1) Thermal properties
Due to hydrogen bonding, water has high melting and boiling points, high
latent heat of vaporization and high specifc heat capacity.
Benefit
These thermal properties cause water to be liquid in most habitats on Earth, making it suitable for living organisms as well as makes it an efective coolant in leaves or in sweat.
2) Cohesive / adhesive properties
Cohesion – Water sticking to other molecules
Benefit
Strong pulling forces can be exerted to suck columns of water up to the tops of the tallest trees in tubes called xylem vessels. These columns of water rarely break despite the suction forces.
Adhesion – Water sticking to other water molecules
Benefit
Adhesive forces between water and cellulose in cell walls in the leaf cause water to be drawn out of xylem vessels, keeping the cell walls moist and able to act as a gas exchange surface.
Significance of Cohesive and Adhesive Properties:
The cohesive properties of water explain its surface tension
A) The hydrogen bonding between water molecules allows the liquid to resist low levels of external force (surface tension).The high surface tension of water makes it sufficiently dense for certain smaller organisms to move along its surface
The adhesive properties of water explain its capillary action
B) Attraction to charged or polar surfaces (e.g. glass) allows water to flow in opposition of gravitational forces (capillary action). This capillary action is necessary to allow water to be transported up plant stems via a transpiration stream
3) Solvent properties – Water dissolves polar and ionic substances (forms competing polar associations to draw materials apart)
Benefit
Most chemical reactions take place with all of the substances involved in the reaction dissolved in water, so water is the medium for metabolic reactions
