Water Flashcards
What is a hydrogen bond?
The weak attractive force between a hydrogen atom with a partial positive charge and an atom with a partial negative charge, usually oxygen or nitrogen.
What is water a medium for?
Metabolic reactions
What are metabolic reactions?
Chemical reactions that occur inside all living cells.
Describe the structure of a water molecule describing the bonds in detail. [6]
- The water molecule is a dipole, which means that it has a positively charged end (hydrogen) and a negatively charged end (oxygen), but no over all charge.
- A molecule with separated charges is ‘polar’.
- The charges are very small and are written as δ+ and δ-, to distinguish them from full charges, written as + and -.
- Hydrogen bonds can form between the δ+ on a hydrogen atom of one molecule and the δ- on an oxygen atom of another.
- Hydrogen bonds are weak, but the very large number of them present in water makes the molecules difficult to separate.
- This therefore gives water a wide range of physical properties vital to life.
What are eight important properties of water?
- Solvent
- Metabolite
- High specific heat capacity
- High latent heat of vaporization
- Cohesion
- High surface tension
- High density
- Transparency
How does water act as a solvent and give example(s).
- Because water molecules are dipoles, they attract charged particles, such as ions, and other polar molecules, such as glucose.
- These then dissolve in water, so chemical reactions can take place in solution.
- Water acts as a transport medium
-E.g. In animals, plasma transports dissolved substances
In plants, water transports minerals in the xylem, and sucrose and amino acids in the phloem.
-Non-polar molecules, such as lipids, do not dissolve in water.
Water is a metabolite. Describe this in detail.
- Water is used in many biochemical reactions as a reactant
- E.g. With CO2 to produce glucose in photosynthesis.
-Hydrolysis: where water splits a molecule. E.g.
Maltose + water= glucose + glucose
-Condensation reactions: where water is a product. E.g.
Glucose + fructose= sucrose + water
Describe high specific heat capacity and give two examples.
- This means that a large amount of heat energy is required to raise water’s temperature.
- This prevents large fluctuations in water temperature.
- This is important in keeping aquatic habitats stable, so that organisms do not have to adapt to extremes of temperature.
- It also allows enzymes within cells to work efficiently.
Describe high latent heat of vaporization and give an example.
- This means that a lot of energy is needed to change it from a liquid to a vapor.
- This is important, for example, in temperature control, where hear is used to vaporize water from sweat on the skin or from a leaf’s surface.
- As the water evaporates, the body cools.
Describe cohesion and give an example.
- Water molecules attract each other forming hydrogen bonds.
- Individually these are weak but, collectively, the molecules stick together in a lattice.
- This sticking together is called cohesion.
- E.g. It allows columns of water to be drawn up xylem vessels in plants.
Describe high surface tension and give an example.
- At ordinary temperatures, water had the highest surface tension of any liquid except Mercury.
- E.g. In a pond, cohesion between water molecules at the surface produces surface tension so that the body of an insect, such as the pond skater, is supported.
Describe high density and give an example.
- Water is denser than air and, as a habitat for aquatic organisms, provides support and buoyancy.
- Water has a maximum density at 4°c.
- Ice is less dense than liquid water, because the hydrogen bonds hold the molecules further apart than they are in liquid.
- Therefore, ice floats in water.
- It is a good industries and prevents large bodies of water losing heat, so organisms below it can survive.
Describe transparency and the importance of it.
- It allows light to pass through.
- This allows aquatic plants to photosynthesise effectively.
What does the term dipole mean?
A polar molecule, with a positive and a negative charge, separated by a very small distance.
