20751733
Description
Flashcards by Marissa Alvarez, updated more than 1 year ago
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Created by Marissa Alvarez
about 4 years ago
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| Question | Answer |
| Concepts 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 |
| Water has several unique properties that permit life: | Small size Chemical stability Low viscosity Biochemical reactant. H and O are major elements of life Polarity |
| WATER 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 |
| Electrostatic interactions 1. Charge - Charge | |
| Electrostatic 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 & acceptor |
Direction
colinear (straight)
sharing
Image:
H20 (binary/octet-stream)
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| Hydrogen 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 |
| 3. 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 |
| Water 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 |
| Ion 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 |
| [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 |
| pH 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 |
| Weak acids are only ___ dissociate. Ka is an acid dissociation constant: The same convenience logic as in pH, logarithmic values are used: pKa = -log Ka | partially |
| Henderson--Hasselbalch Equation -The relation between pH and pKa pH = pKa + log ( [proton acceptor] / proton donor]) pKa = pH when [proton acceptor] = [proton donor] |
Image:
Hh+Eqn (binary/octet-stream)
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| Addition 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 curve | buffering midpoint |
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