ch3 Flashcards
How to draw hydrogen bonds between water and how do they form?
- regions of neighbouring water molecules with opposite partial charges are attracted to each other causing a h bond to form.
- due to oxygens electron arrangement it is able to have two hydrogen bonds
- these bonds form break and reform rapidly
what are the 4 properties of water due to its H-bonds?
- Cohesive
- moderates temp changes
- versatile solvent
- ice is less dense
explain each property and its biological importance
-cohesive:
hydrogen bonding keeps water molecules together causing high surface tension
aids in water transport up a plant as it helps keep water together in a column in the cells(with the help of adhesion)
when the water evaporates from the leaves, the evaporation pulls water up from the roots.
-moderates temp changes
has high specific heat 1 cal/g
Water can absorb / release a large amount of heat with only a slight change in its own temp
Water resists temperature changes
Water acts like temperature buffer
high heat of evaporation
The high specific heat of water stabilizes ocean temperatures, creating a favorable environment for marine life.
organisms are made primarily of water, they are better able to resist changes in their own temperature
-ice less dense
H-bonds hold molecules ‘arms length’ apart causing large spaces between each molecules making them less dense
water gets the most dense at 4 C as as there are fewer h-bonds so molecules are able to slip close together but above 4 they start expanding again as molecules move faster.
if ice sank then lakes and oceans would freeze destroying the aquatic environment hence ice being able to float provides a stable environment underneath, the solid ice also provides a habitat for animals such as polar bears
-water is a versatile solvent
dissolving agent is a solvent and substance being dissolved is solute
even molecules as large as proteins can dissolve due to ionic and polar bonds
Substances that are non-ionic and non-polar repel water as they are hydrophilic
Working inward from the surface of each salt crystal, water eventually dissolves all the ions. The result is a solution of two solutes
polar compounds and ions are dissolved in biological fluid such as blood and sap of plants
• What is polarity?
having poles or being polar
• describe the polarity of water?
polarity of water creates a slightly positive charge on hydrogen and a slightly negative charge on oxygen due to oxygen being more electronegative then hydrogen
• what is dipoles ? explain why they occur
a pair of equal and opposite electric charges separated especially by a small distance.
occur when two atoms in a molecule have substantially different electronegativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive
• why is water polar ?
Water is polar because of the V shape of the molecule and unequal sharing of electrons due to oxygen being more electronegative.
what is surface tension?
measure of how hard it is to break the surface of a liquid
• Define kinetic energy
energy that it possesses due to its motion.
• define thermal or heat energy
energy that is generated and measured by heat.
is produced when a rise in temperature causes atoms and molecules to move faster and collide with each other.
• define temperature
it is the average kinetic energy of molecules
• define heat transfer
transfer of heat from hot region to cold region until temperature is the same
• define calorie
amount of heat it requires to raise 1 g of water by 1 C
• define kilocalorie
unit of energy of one thousand calories
joule to cal
1J = 0.239 cal
• define specific heat
amount of heat that need to be absorbed/lost for 1g of that substance to change its temp by 1 C
• what is the specific heat of water in cal and J
1 cal/g C
4.18J
• what is heat of evaporation
heat a liquid must absorb for 1 g to be converted to gas
• what is water’s heat of evaporation in Cal
580 cal
• Describe what is evaporative cooling and how it takes place
occurs because molecules with greatest kinetic energy are the ones to leave first as gas and that contributes to stability of temperature in lakes and such
Heat is transferred from the skin to the water molecules (sweat)
Water molecules evaporate, they take a lot of heat energy with them
The average temp of the molecules
left behind is lower.
• what is hydration shell ?
-sphere of water molecules around diissolved ions
Explain how polar and ionic substances dissolve in water
When you immerse an ionic compound in water, the ions are attracted to the opposite charges on the water molecules
If the attraction between the ions and the water molecules is great enough to break the bonds holding the ions together, the compound dissolves
The sphere of water molecules around each dissolved ion is called a hydration shell.
Working inward from the surface of each salt crystal, water eventually dissolves all the ions.
Distinguish between the following sets of terms: hydrophobic and hydrophilic substances
- hydrophobic= non-polar bonds that repel water
- hydrophillic= polar bonds that attract water
how do we calculate molarity
M= n/volume in L
Define acids and bases and pH.
- acids= donate a proton ,increase [h+]
- base=accepts a proton ,decrease [h+]
- pH is the measure of how acidic or basic a solution is
how to work out pH
-log[H+]
Explain how a buffer works and the significance of buffers in living systems. Give an example of such a buffer system.
- substance that minimizes changes in concentration of H+ and OH^-
- It does so by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted.
- in blood H2CO3 donates H+ when pH is rising and HCO3^- accepts H+ when pH is dropping.
describe ocean acidification
When CO2 dissolves in seawater, it reacts with water to form carbonic acid, which lowers ocean pH. This process, known as ocean acidification
why is calcium carbonate depleting and what is it used for
- carbonic acid is dissociating to form H+ ions and then causing the carbonate ions in water to react with them to form bicarbonate ions instead of the carbonate ions reacting with the calcium ions Ca^2+ to form calcium carbonate
- it is used for building coral reefs and shells
