water Flashcards
What is the structure of water?
water is made up of two hydrogen atoms covalently bonded to an oxygen atom. oxygen has a higher electronegativity than hydrogen, and attracts the shared electrons more strongly, resulting in poliarity. ( O= s^- H=s^+)
cohesive properties
water can form intermolecular associations with other molecules that share common properties. E.G. poliarity.
- water can form hydrogen bonds with other water molecules ( cohesion: like molecules stick together).
- water can form polar associations with charged molecules ( adhesion: unlike molecules stick together).
the cohesive properties of water result in a relatively high surface tension ( can resist low external forces).
the adhesive properties of water allow for potential capillary action ( transpiration stream in plants).
solvent properties
water is commonly referred to as the universal solvent due to its capacity to dissolve a large number of substances.
-large quantities of water molecules can sufficiently weaken forces (ionic bonds) and form dispersive hydration shells.
Substances that can dissolve in water, are called hydrophilic.
-includes glucose, amino acids, sodium chloride, oxygen (low).
Substances that cannot dissolve in water, are called hydrophobic.
-includes lipids (fats and cholesterol).
these solvent properties make water an important medium for metabolic reactions, as well as necessary transport medium.
thermal properties
water has the capacity to absorb large amounts of heat energy before undergoing a resultant change in state.
water therefore then has a very high specific heat capacity, which is the energy required to increase the temperature of 1g by 1 degree celsius.
these properties then make water a very effective coolant.
-evaporation of sweat requires absorption of heat.
other properties of water
water is transparent, allowing light to pass through it.
-important for photosynthesis and vision
water expands when frozen, becoming less dense.
-important for life on earth as it means ice floats and the oceans underneath don’t automatically freeze
Water Vs Methane
water and methane differ in thermal properties, despite having similar structure (comparable weight, size, valance structure).
the differences are due to the polarity of water and its capacity to form intermolecular hydrogen bonds.
Mehane:
formula- CH4
polarity- non-polar
heat capacity- 2.20
boiling point- -161
Water:
formula- H2O
polarity- polar
heat capacity- 4.186
boiling point- 100
What is a condensation reaction?
a condensation reaction occurs when two molecules combine to form a more complex molecule, with the removal of water.
What is a hydrolysis reaction?
a hydrolysis reaction is when larger molecules are broken down into smaller ones, with the addition of water.
