Biochemistry (water)
Which angle between the two electronegative O atoms will form the strongest hydrogen bond?
180 degree angle
Water is densest at __ degrees Celcius
4 degrees Celcius
How many hydrogen bonds does water form as ice?
4 hydrogen bonds per water molecule
At less than __ degrees, a hydrogen bond will NOT be able to form
90 degrees
Which is more electronegative, oxygen or hydrogen?
Oxygen
The lower the pKa, the ____(larger or smaller) the Ka, and the ____ (more or less) acidic the compound is
larger; more So: the lower the pKa, the larger the Ka, and the more acidic the compound is
What is the shape of a water molecule?
A water molecule is SP3 hybridized.
The magnitude of the pH reveals the ___
Acidity of the solution
Compare different properties of acids and bases
Acids have a sour taste and have a pH below 7. Bases have a bitter taste, feel slippery, and have a pH above 7
Why does Ka = Kw?
Because Ka=[H+][OH-]/[H2O] and [H2O]=1. And Kw = [H+][OH-]
What makes water a polar molecule?
Difference in electronegativity between H and O and the bent geometry.
True or False: pH is temperature dependent while pKa is not.
FALSE. Both pH and pKa are temperature dependent
As pH goes up, more ___ will dissociate into ___.
HA; A-
What are some benefits of water having high specific heat capacity?
High specific heat means that it takes a lot of energy to change the temperature of water. This makes water a good insulator and coolant.
What are three resultant properties of water due to cohesion?
High surface tension Strong Capillary action High specific heat capacity
What property of water allows for it to have high cohesion?
Hydrogen bonding (water molecules stick together)
What happens to the hydrogen bond as the angle decreases between the two O atoms?
Hydrogen bonds become weaker
How is the ratio of the concentration of [A-]/[HA] affected by pH and pKa?
In the henderson-hasselbach equation you take the difference between the two and that gives you what the ration is to the power of 10 because you take 10 to the power of pH-pKA.
What is water cohesion?
Individual water molecules sticking to each other
Intermolecular force as opposed to intramolecular force
Intermolecular forces like hydrogen bonding are between to molecules while intramolecular forces are between the atoms in one molecule.
Water is an excellent solvent for which compounds?
Ionic and polar covalent
What is the definition of a hydrogen bond?
It is a weak electrostatic interaction between an electronegative atom (N,O, or F) and a hydrogen atom bount to another electronegative atom (N,O, or F).
What is Kw?
Kw is [H+][OH-] in water. It = 1x10^-14 M^2
Explain why the pH of pure water is 7 at 25 C?
Pure water ionizes itself at a small degree. Using the H-H equation, you find that the [H+] = 10^-7 and [OH-]= 10^-7; they are both equal.
Henderson-Hasselbalch equation
Shows the relationship between pH, pKa, and concentrations of weak acid and conj base
Is pH a property of the solution or solvent?
Solution
What is the Bronsted-Lowry definition of an acid?
Species that donates a proton (H) in a reaction
What is the Bronsted-Lowry definition of a base?
Species that receives a proton (H) in a reaction
What is the angle between the hydrogen-oxygen bonds in a water molecule?
The angle is 104.5 degrees, giving water its bent shape.
What is the reason for water's bent position?
The lone pairs on the oxygen give water its bent position. Their electron clouds take up extra space (more than the bonds) and push them towards each other.
Water is able to form hydrogen bonds as a result of what?
The polarity of the water molecule, because a hydrogen bond is the weak electrostatic interaction between an electronegative atom and a H bound to another electronegative atom
What is Keq?
The ratio of products over reactants. Keq= [H+][OH-]/[H2O]
What is unique about weak acids and weak bases in a solution?
They only partially ionize
Why can some insects walk on the surface of water?
This is due to high surface tension. The water molecules at the surface cohere more strongly to each other because they are not completely surrounded on all sides by other water molecules, therefore the H bonds are stronger and shorter.
Describe why water has strong capillary action?
This results from cohesion and adhesion. Cohesion is the ability of water molecules to stick to one another. Adhesion is the ability of water molecules to stick to another surface. Therefore, water can adhere to a surface, such as a straw, due to adhesion and pull other water molecules with it due to cohesion.
Water is amphoteric- explain.
Water can act as either an acid or a base. Either donating a hydrogen atom or accepting one.
What is a hydrogen bond in water?
When the positive charge of one water molecule attracts the negative charge of an oxygen on another water molecule.
Why does the bottom layer of water in a lake or pond stay liquid, while the top freezes?
When water freezes to ice it creates 4 hydrogen bonds that are longer than regular H bonds. Therefore, ice is less dense than liquid water, which allows it to float to the surface while the rest of the water underneath remains liquid.
As the concentration of H+ increases, pH _____ (increases or decreases)
decreases
The magnitude of pKa reveals ___
how strong of an acid a compound is (how much it dissociates)
What is pKa a property of?
pKa is a property of the solute (acid), and it is not affected by pH, [A-], or [HA]
