Lecture 1 Water, Acids, Bases and Buffers

What is the property of water? what kind of compounds does it dissolve? How does it interact? pH? Shape of water molecule?

-It is a Polar molecule

-dissolves hydrophilic compounds

-interacts through hydrogen bonds

-pH of 7

-asymmetrical shape 

-highest heat capacity

-only substance naturally in all 3 states

What is polarity caused by?

-the difference in electronegativity

what is eletronegativity?

-An atom’s attraction to electrons

Hydrophilic molecules in water are?

-soluble in water

-usually polar molecules

Hydrophobic molecules in water are?

-not soluble in water

-usually non-polar molecules

what is amphipathic/amphiphilic?

-both hydrophilic and hydrophobic regions

what two major forces stabilize hydrophilicity?

-electrostatic attraction (ion-dipole, dipole-dipole)

-hydrogen bonding 

What are the 4 different weak noncovalent bonds?

1. Hydrogen bonds

2. ionic interactions 

3. hydrophobic interactions 

4. van der waals interaction 

What is a Hydrogen bond?

-a weak bond involving a hydrogen donor and an acceptor

Why are hydrogen bonds disrupted by water?

-there is a competition for donor and acceptor

What is a hydrophobic interaction?

-a passive interaction that doesn’t need energy input. 

-It minimizes the loss of hydrogen bonds between water molecules

What powers protein folding?

-the hydrophobic effect

-hydrophobic residue hidden inside while hydrophilic residue is exposed 

what is the van der waals interaction?

-nonspecific interaction of any 2 atoms within 3-4 A of each other 

-via electrostatic interaction by transient asymmetric distribution of electronic charge around an atom 

What are the functions of weak bonds?

-a large number of weak bonds may contribute to stability

-allow for transient and specific interactions

What are the 4 hydrogen concentrations of pH?

1. Hydrogen ion (H+)

2. Hydride (H-)

3. Hydrogen (H)

4. Hydroxide (OH-)

Acid/Base which is the donor and the acceptor?

-Acid is the proton donor 

-Base is the proton acceptor 

What is the difference between a strong acid and a weak acid and base?

-Strong acids and bases are completely ionized in an aqueous solution 

-Weak acids and bases are incompletely ionized in aqueous solutions

Is water ionized?

-to a small extent water is ionized

-the ion product of water is constant at a specific temperature 

What is pH and pOH?

-pH = -log₁₀[H+]

-pOH = -log₁₀[OH-]

what is a constant for a water based solution and at what temperature?

-Kw(10¹⁴M²) is a constant at 25*C

What is the definition of pKa for weak acids and bases?

-HA is a weak acid with A- as the conjugate base 

-A- is a base and HA is the conjugate acid 

pH = pKa when?

[A-] = [HA]

what is the equilibrium constant and what defines pKa?

-Ka

-log(1/Ka)

The formula for a base/acid conjugate acid varying on pH

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

If pH>pKa & log[A-]/[HA]>0 means?

if pH<pKa & log[A-]/[HA]<0 means?

-base form dominates 

-acid form dominates 

What is titration?

-an acid neutralized by an increasing amount of base or vice versa

what generates buffering (smaller pH change)?

-the same amount of OH- being added

What is a buffer?

-a solution (weak) whose pH resists change when small amount of acid or base is added

What is used as buffer system? what is not used?

-usually weak acids and bases

-no buffering using water 

What is an equivalence point?

-ideal point where all the (titrant) starting acid or base is neutralized 

What effects buffer capacity?

-concentrations of the buffer (higher conc.=higher buffer copacity) 

what is the best buffering capacity at?

-when pH is close to pKa

which reaction buffers pH in the blood?

what happens if too much acid is added to the blood?

-reaction 2

-reaction 2 moves left releasing CO2 via reaction 1 using respiration