Karteikarten
Lecture Four - Properties of Water & Acids, Bases, Buffers
Karten in diesem Stapel (17)
- 1Concepts to understand-Water has unique properties that are essential for life
-Weak interactions: H-bond, Van der Waals
Ion product of water
-pH
-pKa
-Henderson - Hasselbalch equation
-Titration and buffers - 2Water has several unique properties that permit life:Small size
Chemical stability
Low viscosity
Biochemical reactant.
H and O are major elements of life
Polarity - 3WATER Polarity makes water a perfect ___ for polar substances. Ionic solids dissolve in H2O to form ___ ions. Polarity is also essential for the formation of micelles (soap) and bilayers (__ ___). Non-polar substances are ___ in water.solvent
hydrated
cell membranes
insoluble - 4Electrostatic interactions 1. Charge - Charge
- 5Electrostatic interactions 2. Hydrogen Bonds H bonds & properties of water: -high boiling point -high melting point -heat of vaporization -heat capacity -surface tension -viscosity ___ of H bond is important for STRENGTH --> Strongest when ___ Partial electron pair ___ occurs b/w donor & acceptorDirection
colinear (straight)
sharing
- 6Hydrogen bonds ___ double helix structure in DNA H bonds stabilize protein ___ structure (i.e. beta sheets). Important concept: The ___ effect of many weak interactions could be a strong force Water can form H bonds with??stabilize
secondary
cumulative
F, O, N ("Phone") and with itself - 73. Van der Waals interactions the interaction between permanent or transient __ of two molecules'. This technically includes the hydrogen bond interactions. However, H- bond is often separated as a special case. There are classes of interactions can be distinguished: 1. Between two dipoles (two H20 molecules) 2. Between a dipole and non-polar atoms (Debye force) 3. Between non-polar atoms (___ ___ force) In 2 and 3, non-polar atoms get polarized by the neighbor *Van der Waals interactions are forces that can be BOTH ___ and ___dipoles
London Dispersion
attractive and repulsive - 8—
- 9—
- 10—
- 11Water auto-ionization Because of electron-rich O atom, H20 is a ___ It attracts (rather attacks) a positively charged (electron-deficient atom). A water molecule may attack another __ molecule to cause ionization. --> The result is hydronium (H3O+) and hydroxide (OH-) ions.nucleophile
water - 12Ion product of water __ = ion product of water Kw = 1X10^-14 IMPORTANT: Kw does __ change when acid or base are added to the solution, assuming [H2O] does not change significantly.Kw
NOT - 13[H+] is an important biochemical parameter pH = -log [__] In pure water [H+] = 10^-7 and pH = 7 In blood = about __ IN tumors pH is often <7 *The "right" pH is required for enzymes to function.H+
7.4 - 14pH values depend on the degree of ____ dissolved in water molecules, such as acids and bases. HCI is an example of a strong acid, it dissociates almost ___ Example: If 1mM HCI is prepared, pH= -log(0.0001) =3 [H+][OH-] = 10^-14 (Kw) **If a low concentration of acid added in a lot of water, the diluted water dominates and the pH remains close to __ (cutoff around 1 micro Molar - 10^-6)dissociation
completely
7 - 15Weak acids are only ___ dissociate. Ka is an acid dissociation constant: The same convenience logic as in pH, logarithmic values are used: pKa = -log Kapartially
- 16Henderson--Hasselbalch Equation -The relation between pH and pKa pH = pKa + log ( [proton acceptor] / proton donor]) pKa = pH when [proton acceptor] = [proton donor]
![Henderson--Hasselbalch Equation -The relation between pH and pKa pH = pKa + log ( [proton acceptor] / proton donor]) pKa = pH when [proto...](https://examtimeassets.s3.amazonaws.com/uploads/media/image/23937881/desktop_5bd7ddb2-e0d6-4fd3-a885-d077e2e4cd4a.png)
- 17Addition of NaOH to a solution containing a weak acid and its conjugate base does not substantially change pH in the region pH=pKa ±1. This phenomenon is called ___. Equilibrium shifts to offset +/-[OH] pH = pKa at the ___ of the titration curvebuffering
midpoint