Properties of water Flashcards
What are the unusual features of water?
Ice has a lower density than water
There is a high surface tension (allows high density structures to lay on top)
There is a high specific heat capacity (can absorb and lose heat without changing the overall temperature much)
High heat of vaporisation
Why is water described as a universal solvent?
Due to the polarity of water molecules. Water molecules are polar as the higher electronegativity of hydrogen means they pull the shared electrons closer to their nucleus. Oxygen is left with a partially positive charge. The opposing charges are attracted to each other and thus hydrogen bonds are formed
What are ions?
Ions - atoms which have lost electrons
(usually metals forming +ve cations)
or gained electrons (usually nonmetals forming -ve anions)
Define ionic compounds
Ionic compounds - oppositely charge
ions are attracted to each other by
electrostatic forces forming a molecule
held together by ionic bonds
What are hydrophilic molecules?
Hydrophilic molecules are attracted to water. Ionic compounds and polar compounds are in this category.
In ionic compounds the polar water is attracted to the oppositely charged ions. As they dissolve, this prevents them binding again. In polar molecules the charged regions on water are attracted to the oppositely charged regions in polar molecules
What are hydrophobic molecules?
These are non-polar compounds that do not readily dissolve in water. These are covalently bonded with no charge
What are dissolved substances and how can they be removed?
– atoms/molecules dispersed in water molecules – only 1 phase present – liquid - phase change has to occur to separate out dissolved substance. This can be achieved by distillation (liquid to gas phase) or precipitation (dissolved form together to create solid phase and are precipitated out of the water).
What are suspended substances? how can we separate?
There are 2 phases present (the solid and the liquid) . If they are large enough they will be settle and can be removed by sedimentation.
Can be centrifuged or use a filter too
What is the impact of a temperature increase?
Reduced dissolvability of gases such as oxygen
Increased rate of biological and chemical reactions
alter sensitivity to pollutants
Amplify tastes and odours in water
Give a brief overview of thermal stratification. Mention each season
Due to the impact of temperature ( and other seasonal changes) the layering of water occurs. In the summer there is stratification, with the top layer being the warmest and most oxygenated. In autumn there is no stratification as lower temps cool the top layer(Epilimnion) and winds cause mixing of temp and oxygen throughout. In the winter the stratification occurs again, this time the warmest and most oxygenated water is in the middle(hypolimnion). Then in spring again there is mixing.
What are the layers in thermal stratification?
Epilimnion is the top layer
Hypolimnion is the bottom layer
Thermocline (metalimnion) is transition zone between layers where rapid temperature & density change occurs
What are the standard for water?
It is never going to be pure water. Needs to be palatable. Acceptable levels for taste and odour are decided using DN and TN.
What do we use to measure standard of water
Dilution number and the threshold number. Chemical testing not used as it may be too small to be detected by this method.
What can impact taste and odour?
moulds, algae, chlorination, industrial wastes
What can impact colour?
Algae or dissolved organic substances
