2.1.2 Biological molecules - Water Flashcards
State the elements in a molecule of water
hydrogen and oxygen (H2O)
How is water bonded together?
covalent bonding
Describe how chemical bonding in water gives it two of its important properties. Name the properties.
Due to hydrogen bonding between its molecules; the density of ice is less than water due to hydrogen forming an open type lattice. High surface tension and relatively high viscosity, can act as a solvent for many substances.
Name the four groups of biological molecules.
Carbohydrates, proteins, lipids and nucleic acids.
Describe the structure of water
Oxygen has a partially negative charge (𝛿-) and hydrogen atoms have a partially positive charge (𝛿+).
The shared hydrogen electrons are pulled towards the oxygen atom.
The other side of each hydrogen atom is left with a slightly positive charge (𝛿+).
The unshared negative electrons give it a slight negative charge (𝛿-).
This makes water a polar molecule.
State the properties of water
- Wide temperature range over which water is a liquid
- Water below 4 °C is less dense than water above 4 °C
- High specific heat capacity
- High latent heat of evaporation
- Polar molecule
- Reactant
- Many hydrogen bonds
- Transparent
Describe why water is a good solvent
This is because water is polar, it is attracted to any other substance that is also polar.
The positive and negative regions of the water molecules are attracted to the negative and positive parts of the solute molecules or ions.
The water molecules cluster around these charged parts of the solute molecules or ions and will help them to separate and stay apart. They have now dissolved and a solution has formed.
Ions and polar molecules will dissolve in water but non-polar molecules will not.
water is a universal solvent as it can easily dissolve a lot of substances (alkali and acid). This means that humans and plants can ingest and consume those elements in a passive way.
Describe why it is important for water to have high specific heat capacity
The hydrogen bonds between water molecules absorb a lot of energy.
These hydrogen bonds give water a high specific heat capacity.
This means water doesn’t experience rapid temperature changes.
Water absorbs/loses a relatively large amount of heat before its temperature changes.
This means that it can withstand environmental factors which is beneficial for aquatic organisms. This is because a lot of energy would be required for the temperature of the ocean to change therefore a stable environment remains for aquatic organisms. (large bodies of water tend to stay relatively constant)
Benefits of ice being less dense than liquid water
Ice is less dense than water therefore it floats, this means that the temperature of large bodies of water tend to stay relatively constant as ice is used like insulation.
Describe the role of high latent heat of vaporisation as a property of water
It takes a lot of energy to break the hydrogen bonds between water molecules.
When water evaporates, heat energy, known as the latent heat of vaporisation, helps the molecules to break away from each other to become a gas.
Due to the hydrogen bonds, water has a high latent heat of vaporisation.
Water absorbs a large amount of heat before it turns into water vapour.
The high latent heat of vaporisation makes it a heat sink for living bodies providing cooling effect upon vaporization.
Define Cohesion
the hydrogen bonds between water molecules pull them towards each other, so they stick together.
Good and strong attraction to other water molecules e.g. allows for capillary action, it is a passive process and goes against the force of gravity (important in plants).
Define Adhesion
water molecules can be attracted to surfaces such as narrow tubes e.g. this allows for water to travel up the xylem in a plant
Define Surface tension
At an air-water surface, the cohesion between water molecules produces surface tension as the hydrogen bonds also pull the molecules inwards at the surface.
