2.1.2a- Water Flashcards
What are the elements in water?
Hydrogen and Oxygen
How are the elements bonded together?
Covalent bonding
How does chemical bonding in water give it two of its important properties? Name the properties.
Due to hydrogen bonding between its molecules; the density of ice is less than water (hydrogen forms an open type lattice). High surface tension and relatively high viscosity. Water can act as a solvent for many substances.
What is the structure of water?
1) negative shared electrons are pulled towards the oxygen
2) the other side of the hydrogen atom is left slightly (+)
3) unshared negative electrons gives it a slightly (-) charge
4) this makes water a polar molecule
What are the properties of water?
1) There is a wide temperature range over water which is a liquid
2) Water below 4 °C is less dense than water above 4 °C
3) High SHC
4) High LHOV
5) Water is a polar molecule
6) Water is a reactant
7) Many hydrogen bonds
8) Water is transparent
Property explained: Liquid
- Water molecules always moving around, unlike other liquids: hydrogen bonds always breaking and reforming
- hydrogen bonds make it hard for water to become a gas and escape => more energy required
- water has low viscosity meaning it can flow easier
Property explained: Density
- Water becomes more dense as it becomes colder until around 4°C
- 4°C to freezing point- water is a polar molecule, so water molecules arrange themselves into a structure less dense than liquid water
- The hydrogen bonds fix polar molecules slightly further apart than average distance in liquid state, produces giant, rigid, open structure, with all oxygen at centre of tetrahedral arrangement of hydrogen atoms.
Property explained: Solvent
- good solvent for many substances
- water is polar, means its attracted to any other polar substance
- positive and negative regions of water molecules are attracted to negative and positive parts of solute molecules or ions.
- water molecules cluster around charged parts of the solute molecules or ions and help them to separate and stay apart. They have now dissolved and a solution has formed.
Property explained: Cohesion and surface tension
- hydrogen bonds between water molecules pull them toward each other- cohesion
- at an air-water surface, cohesion between water molecules produces surface tension as hydrogen bonds also pull molecules inwards at surface.
- water molecules attracted to narrow surfaces- adhesion
Property explained: High SHC
- hydrogen bonds between water molecules absorb lots of energy
- these hydrogen bonds give water a high specific heat capacity.
- this means water doesn’t experience rapid temperature changes.
- water absorbs/loses relatively large amount of heat before its temperature changes.
Property explained: High LHOV
- takes lots of energy to break hydrogen bonds between water molecules
- water evaporates, heat energy (LHOV) helps bonds break apart to become a gas
- due to hydrogen bonds, water has high LHOV
- water absorbs large amounts of energyy before evaporating
Property explained: Reactant
- water is reactant for many reactions: hydrolosis, photosynthesis
- properties as a reactant do not directly draw on its polarity
Water properties and significance to life
Ice is less dense than water- ice forms an insulating layer over water
High surface tension- the high surface tension of water means that it can form a habitat on the surface of the water
Strong cohesive properties & high tensile strength- water can be pulled through plants in column as water molecules are held together by H-bonds
Colourless with a high transmission- light can pass through cells for photosynthesis
Liquid at room temperature- can be used for transport and as medium for reactions
High LHOV- can be used for cooling organisms by evaporation of e.g sweat
High SHC- conditions are stable in cells and aquatic environments
