Lecture 4: Properties of Water Flashcards Preview

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Flashcards in Lecture 4: Properties of Water Deck (31)
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1
Q

What is an example of how H bonds have a partial ionic character?

A

H-bonding between water molecules with partial negative and positive charged

2
Q

How many H bonds can a water molecule form? What is important to note about these? Why?

A

4 H bonds with 4 different water molecules. No double dipping!
Because of tetrahedral orientation of the H atoms and lone pair about the central O

3
Q

What can be said about the lifetime of each individual H bond? What can affect it?

A

VERY short

Increasing temperatures = decreasing lifetime of H bonds

4
Q

What confers cohesion of liquid water?

A

H-bonding network

5
Q

What is often the effect of dissolution on enthalpy?

A

Breaking of enthalpically favorable interactions

6
Q

What happens to the H+ atoms after water ionizes?

A

Instantaneously hydrated to form hydronium ions (H30+) and are never really found in aqueous solution. So the real reaction looks more like this:
2H2O H3O+ + OH–

7
Q

What is water’s concentration under standard conditions?

A

55.5 M

8
Q

What is the ion products of water?

A

Kw = [H+].[OH-] = 10^-14 M^2

9
Q

What is the equation to calculate pH?

A

pH = log 1/[H+] = – log [H+]

10
Q

What does alkaline mean?

A

Basic

11
Q

What does a change of pH of 1 unit correspond to in terms of concentration?

A

10 fold concentration change

12
Q

What is the pH of arterial blood?

A

7.41

13
Q

What is the pH of venous blood?

A

7.38

14
Q

What can be said of aqueous solutions at equilibrium?

A

They maintain electrical neutrality: # of anions = # of cations

15
Q

What is the difference between strong and weak acids?

A

Strong acids completely dissociate into their component ions in solution

16
Q

What is Ka? How to calculate it?

A

The characteristic equilibrium constant of weak acids

Ka = [H+].[A-]/[HA]

17
Q

What is the pKa equation?

A

pKa = - log Ka

18
Q

How many pKas do polyprotic acids have?

A

1 for each H released

19
Q

What does a lower pKa mean?

A

Stronger tendency to release the H

20
Q

Why are weak acids good buffers? When are they optimal and why?

A

Because they only dissociate partially there is both HA and A- in solution.

  • When you add a strong acid, the A- reacts with it to produce water: very small pH change
  • When you add a strong base the HA reacts with it to produce water: very small pH change

They are optimal at a pH equal to their pKa (within a 1 pH unit range) because the acid has released 50% of its protons at the pKa: [HA] = [A-]

21
Q

What is the Henderson-Hasselbach equation? What does it mean?

A

pH = pKa + log [A-]/[HA]

Means that when you have more dissociation than not, pH>pKa

22
Q

What molecule is the buffer in our blood?

A

H2CO3

23
Q

What is the reaction to produce H2CO3 in the blood?

A

H2O + CO2 H2CO3 H+ + HCO3-

24
Q

What is carbonic acid’s pKa?

A

3.77 at 37°C

25
Q

How can we adjust blood pH quickly?

A

Breathing!

26
Q

What will happen to the equilibrium between carbonic acid and
bicarbonate if I add a strong acid to this system?

A

Reaction will be driven to form more carbonic acid because more H+ will be available

27
Q

What do we use in clinical medicine as the acid in the HH equation?

A

CO2

28
Q

What is bicarbonate?

A

HCO3-

29
Q

What is the buffer system of mammalian cells?

A

Phosphate System: H2PO4– H+ + HPO42–

30
Q

What do humans do to regulate their blood pH when it drops?

A

Breathe more heavily to get rid of the CO2 faster

31
Q

How can [HCO3-] be adjusted by the human body?

A

Exhalation and renal action