Amino Acids DLA. 2- Water, Bases And The Henderson-hassalbach Equation

Question 1

How does hydrogen bonds determine the “structure” water?

Answer 1

• As a liquid there are always 3-4 hydrogen bonds between water molecules, but water molecules are often tumbling
• when solid, there are always 4 hydrogen bonds between each water molecules(ice)

Question 2

How do hydrogen bonds affect the thermal properties of water?

Answer 2

-Water has a large temperature range for a liquid state

CO2 in comparison is a gas at room temperature because it has no overall dipole

Question 3

Why can water dissolve in polar substances?

Answer 3

Due to the permanent dipole

Question 4

Water may…

Answer 4

Self-dissociate

Question 5

Give equations for water self dissociating

Answer 5

H2O + H2O -> H30+ + OH-

Question 6

What is the equation for pH?

Answer 6

pH= -log[H+]

Question 7

Why may Mg(OH)2 be ingested?

Answer 7

Magnesium hydroxide (antacid, laxative) maybe ingested because it has very low solubility in water, (so some might argue about it being a strong base) but any that dissolves is dissociated

Question 8

Why is Sulfuric acid considered weak ?

Answer 8

Only the first dissociation considered strong, HSO4- is a weak acid , compared to other weak acids it’s quite strong. But since it doesn’t completely dissociate in water, we call it weak

Question 9

Titration: what is the equivalence point? Where is it found?

Answer 9

The equivalence point occurs when an amount of acid is mixed with an equal amount of base

The equivalence is found where 1/2 the region of sharp change in the curve

Question 10

What is the correlation between Ka and acidity?

Answer 10

The higher the Ka the stronger the acid

Question 11

What is the correlation between pka and acidity?

Answer 11

The lower the pKa the stronger the acid

Question 12

What is the equation for pKa?

Answer 12

pKa = -logKa

Question 13

Differentiate the Ka for a wHA and sHA

Answer 13

Ka for a wHA will not be as high as for a sHA

Question 14

Differentiate the pKa of a wHA and a a sHA

Answer 14

pKa of a wHA will be larger than the pKa of a sHA

Question 15

Assess the biological danger of a weak acid

Answer 15

Danger is not related to acid strength:

Ex. HF is a weak acid

• HF is toxic
• HF is toxic at any concentration

Vinegar is 5% acetic acid
Acetic acid is formed in metabolism
Or the same acid maybe toxic if concentrated
-Glacial(pure) acetic avid is toxic at high concentrations

Question 16

What is the buffering region in titration?

Answer 16

The region where the pH changes slowly as H+ or OH- is added during a titration

Question 17

How can the pKa be measured during titration?

Answer 17

Measured as the equidistant part of the curve which changes pH slowly.

When the pH= pKa of the weak acid, there is equal amounts of weak acid and its conjugate base (50% dissociated)

Question 18

How do you find the effective buffering range for a weak acid?

Answer 18

This is when pH is +/-1 of the pKa of the weak acid

Question 19

What are buffers?

Answer 19

Substances that resist a change in pH

Question 20

How are buffers formed?

Answer 20

When a weak acid and a similar amount of its conjugate base are mixed, a buffer is formed

Question 21

What are the major buffers in mammalian systems?

Answer 21

Carbon dioxide, phosphate and proteins

Question 22

Why does phosphoric acid have 3 areas where it can act as a buffer?

Answer 22

It is a triprotic acid

Question 23

What equilibrium constant of pure water?

Answer 23

Keq =[H2O]^2 = Kw= [ HC][OH-]= 10^-14

Question 24

Give the pka formula

Answer 24

pka -logka