Water and Aqueous Solutions

What are some emergent properties of water?

○ Cohesion (sticking together) vs. adhesion (to surface)

○ High specific heat (1 cal/g*C)

○ High heat of vaporization (540 cal/g)

○ Freezing and expansion

○ Versatile solvent

○ Medium and ingredient for biochem rxns

○ Water is tetrahedral

How does water support life?

Biological - a source of electrons and protons
Chemical - neutral pH; polar solvent and medium to transport nutrients; H-bonding causing cohesion and adhesion

Physical - high specific heat; high heat of vaporization; expansion upon heating

Water based solutions look like:

solvent + solute → solution

What are the two major properties of aqueous solutions?

1. Solute concentration

2. pH (measure of H+ concentration)

one mole

6.022×10²³

From solid to liquid solution:

MW(g/mol) x Molarity(mole/l) x V(L) = g required

From a stock/concentrated solution to a diluted solution:

C1V1 = C2V2

Dissociation in pure water

H2O → [OH-] + [H+]

pH meaning

power of Hydrogen; negative log of [H+]

What makes a solution acidic?

Acid donates protons and increases the [H+] concentration → decreases pH

What makes a solution basic?

Bases accept protons and decrease the [H+] concentration → increases pH

Buffer

Resists a pH change in a solution within a range by accepting or donating protons

What do buffers do in biology

buffers donate protons when the pH increases and accept protons when the pH decreases

pK

the pH at which the acid to base ratio of a buffer is 1:1

different biological buffers

phosphate; carbonate-bi-carbonate

Trizma Buffer

used for DNA, RNA: pK 8.1

characteristics of an amino acid buffer:

amine group - weak base

carboxyl group - weak acid