1. SOLUTIONS and pH

2. Most reactions in living things occur in solutions, which are mixtures where one substance is even distributed in another. Since living things are mostly made of water, our reactions usually occur in aqueous solutions.

3. Solutions!!! SOLUTES + SOLVENTS:
The solute which is the substance being dissolved.
ie. NaCl (salt), C6H12O6 (sugar)
The solvent which is the substance that the solute is dissolved into.
ie. water, alcohol
The concentration is the amount of solute dissolved in a fixed amount of solvent.
ie. 3% saltwater, 0.9% sugarwater
A saturated solution has as much solute dissolved into it as possible

4. In this solution, salt is the solute and water is the solvent.

5. Acids and Bases
These are solutions made by the dissociation (break-up) of a water molecule.
Water naturally breaks down into ions of opposite charges, this is called dissociation.
Dissociation has 2 steps:
H H+ + OH- + H H30+ + OH-
excessive number of these ions results in an acidic solution
excessive number of these ions results in a basic or alkaline solution

6. What does it mean to be acidic, basic, and neutral?
All biological solutions are categorized based on the amounts of: OH- = hydroxide ion
H30+ = hydronium ion
If H30+ = OH-, solution is neutral.
If H30+ > OH-, solution is acidic.
Characteristics of acids: pH < 7, sour, corrosive
If H30+ < OH-, solution is basic.
Characteristics of bases: pH > 7, bitter, slippery

7. How do we measure acidity or alkalinity (basic)?
The pH scale is a scale used to compare the relative amounts of hydronium and hydroxide ions in a solution. It ranges from 0 – 14.
0 is very acidic; 7 is neutral; 14 is very basic.
The pH scale is based on a logarithmic scale, which means the change from 4 to 5 pH means it has 10x more OH- ions.

9. What is a buffer? Why do we need them?
A buffer is a substance that can neutralize small amounts of acids or bases (ie. Tums, Pepto Bismol, Alka Seltzer).
Buffers are necessary to protect living things since enzymes can only work in narrow pH ranges.
For example: Your stomach and intestines
have different pH’s because of
their enzymes.