BCH 261 Lecture Notes - Lecture 2: Weak Base, Buffer Solution, Osmotic Pressure

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violetfish575

4 Mar 2017

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Document Summary

The bulk movement of water across a semi-permeable membrane into another aqueous compartment containing solute at a higher concentration. Isotonic solution: equal osmolarity inside and outside the cell. Hypersonic solution: cell is bathed in a solution with higher osmolarity than cytoplasm. Hypotonic solution: cell is bathed in a solution with lower osmolarity than cytoplasm. Cells are full of (cid:862)solutes(cid:863): high os(cid:373)olarity: therefore, mammalian cells pump na+ and cl- to the extracellular fluid to balance osmolarity. Plant and bacterial cells: use cell wall to prevent swelling. Weak base: partially ionized to accept h+ Weak acid or weak base solution will form a conjugate acid/base system. Weak acids and weak bases reach a chemical equilibrium defined by the acid constant, ka. The stronger the acid, the larger the ka value. Possible to rate weak acids (or conjugate acids of weak bases) using the ka. Ka values can be converted to a -log scale just like ph and poh.

Related Questions

1) This is a thermodynamics questions

In your body, normal osmolarity of blood serum is just under 0.3 molar. Because cell membranes are permeable to water, the osmolarity of intracellular fluid is approximately equal to that of extracellular fluid (though the intracellular and extracellular composition in terms of specific ions and proteins is quite different). As an aside, measurement of osmolarity of serum is an important clinical test used to check for dehydration or other imbalances of water and electrolytes.

a) In the supplemental information, the osmosis example presented involves sucrose as a solute, but the van't Hoff equation also applies for other solutes. Using this formula (â = cRT, where â is the excess pressure), calculate the osmotic pressure associated with 0.3 molar concentration of osmolytic particles (e.g., ions, proteins, or other dissolved particles) in contact with pure water through a semi-permeable membrane at physiological temperature of 310 K. Express your results in atmospheres of pressure (1 atmosphere of pressure is 1.0x10⁵ Pascal, where 1 Pascal is a Newton/m²).

b) A biological cell membrane is a bilayer of phospholipid molecules, only a few nanometers thick, and can basically be thought of much like a soap bubble, except immersed in aqueous solution. If cells are placed in pure water, they often swell and burst in just a few minutes. Explain why this would happen.

grayporcupine495

Unlike strong acids and bases that ionize completely in solution, weak acids or bases partially ionize. The tendency to ionize (i.e., the ionic strength) of a weak acid or base can be quantified in several ways including

Ka or Kb,

pKa or pKb,

and percent ionization.

Part A

Pyridine is a weak base that is used in the manufacture of pesticides and plastic resins. It is also a component of cigarette smoke. Pyridine ionizes in water as follows:

C5H5N+H2OâC5H5NH++OHâ

The pKb of pyridine is 8.75. What is the pH of a 0.455 M solution of pyridine?

Express the pH numerically to two decimal places.

pH=____________

Part B

Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodium benzoate, is a preservative found in foods, medications, and personal hygiene products. Benzoic acid dissociates in water:

C6H5COOHâC6H5COOâ+H+

The pKa of this reaction is 4.2. In a 0.58 M solution of benzoic acid, what percentage of the molecules are ionized?

Express the percentage numerically using two significant figures.

percent ionized = _______________ %

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Question 5

At a constant temperature, if you increase the number of unsaturated fatty acid chains in the phospholipid, the membrane will become......

less fluid

more fluid

fluidity will be unchanged

Question 6

Bacteria in a hot spring at 80 degrees celsius would be expected to have ______________ in their cell membrane

high proportions of saturated phospholipids

high proportions of unsaturated phospholipids

an equal ratio of saturated to unsaturated phospholipid

Question 7

Membrane proteins have an important role in membrane fluidity

True

False

Question 8

The HIV virus can't attach to cells that have a mutation in the CCR5 gene and so such individuals are resistant to HIV. What population of people have a higher incidence of the mutant CCR5 gene and why?

europeans because their ancestors survived the bubonic plague

North Americans because their ancestors survived small pox

europeans because they have a longer evolutionary past with HIV

Africans because they have a longer evolutionary past with HIV

Question 9

Nematode trapping fungi have ______________ molecules called ______________ that recognize specific carbohydrates on the surface of the nematode worms. This is how a fungus can recognize that its prey, the nematode worm, has wriggled into the loop. Write two words on lowercase separated by a space with no other syntax

Question 10

Diffusion requires energy

True

False

Question 11

The net direction of molecule movement when molecules diffuse is

down their concentration gradient

random directions

Question 12

In osmosis, water molecules from a solution of higher solute concentration cross a semi-permeable membrane into a solution of lower solute concentration?

True

False

Question 13

Which best defines osmosis?

In osmosis, water from a solution of lower solute concentration move across a semi-permeable membrane into a solution of higher solute concentration?

In osmosis, water from a solution of higher solute concentration move across a semi-permeable membrane into a solution of lower solute concentration?

Question 14

Animal cells placed into a hypotonic solution would most likely?

lyse (burst)

shrink

remain unchanged in size

Question 15