Lecture 2 Flashcards
Why is water polar?
The differences in the electro negativity between the atom of oxygen and the atom of hydrogen
Oxygen is more electronegative and therefore attracts the electrons from the hydrogen more strongly
This results in a molecule which has a side partially negative and a side partially positive.
The properties of water
Cohesive behavior
-Cohesion and Adhesion
-Surface Tension
Ability to moderate temperature
-High Specific Heat
-Stabilizing Temperature
Expansion upon freezing
-Floating of Ice on Liquid Water
Versatility as a solvent
What is cohesion and adhesion?
The attractions between adjacent polar molecules form a webwork of hydrogen bonds. These bonds are responsible for cohesion and adhesion
One result of cohesion is surface tension
Why is water carried up a tree trunk?
Adhesion- the bonding of the water molecules to the plants cell walls, which helps resist the pull of gravity
Cohesion - the bonding between water molecules, which holds together the column of water
Water’s temperature affect its density
Density decreases with an increase of temperature, but below 4° C, density decreases with a decrease in temperature
Why does ice float?
The density of ice is less than the density of liquid water
Why does ice have less density than water?
Water molecules in ice are farther apart compared to liquid water
Water has a high heat capacity, what does this mean?
This means it resists changing temperature when heat is added or removed
Why can marine animals live in a frozen lake during winter?
Expansion upon freezing
What effect is produced by the high surface tension of water?
A water strider can walk across the surface of a small pond
Which chemical bonds are responsible for the surface tension of water?
Hydrogen bonds
Why is water an excellent solvent?
Due to its polarity
What is a solvent?
The dissolving agent of a solution
What is the solute?
The substance that is dissolved
What is un aqueous solution?
A solution where water is the solvent
A water-soluable protein
Water can dissolve compounds made of non-ionic polar molecules
Hydrophilic and hydrophobic substances
A hydrophilic substance has an affinity for water whereas a hydrophobic substance does not have an affinity for water
(Not all hydrophilic substances are dissolved by water. Eg. Cotton)
What is an acid?
An acid is a substance that increases the hydrogen ion concentration of a solution
What is a base?
A substance that reduces the hydrogen ion concentration of a solution
What is the symbol for hydrogen ion?
H+
What is the symbol for hydroxide Lons?
OH-
What is the pH of a solution defined as?
The negative logarithm (base 10) of the H+ concentration
pH = - log [ H+]
pH decreases when
H+ concentration increases
What is the basis of the pH scale?
Hydrogen ion (H+1)
Lower H+ concentration = lower pH (acidic)
Greater H+ = higher pH (basic)
What is the pH value range of most biological fluids?
6 to 8
What are buffers?
Substances that minimize changes in concentrations of H+ and OH- in a solution
The internal pH of most living cells
Must remain close to pH 7 ( 7.4 - 7.7 )
What are the pairs of buffer solutions?
- A weak acid plus a salt derived from that weak acid
- At weak base plus a salt of that weak base.
