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76 Cards in this Set
- Front
- Back
T or F: Water is abundant in living organisms |
True |
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Why does water have tetrahedral geometry? |
Because of its electronic structure |
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What are the two primary characteristics of the electronic structure of water? |
1. Oxygen has two lone pair 2. An electron from hydrogen is shared with one from oxygen |
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Is water polar or nonpolar? |
Polar |
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T or F: Same charges attract |
False |
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What is the charge of oxygen? |
Partial negative charge |
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What is the charge of hydrogen? |
Partial positive charge |
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How are the oxygens affected in the way water molecules orient? |
Oxygens are positioned near hydrogen(s) in a neighboring molecule |
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What is a hydrogen bond? |
A noncovalent interaction between a molecule containing an electronegative atom and another molecule containing an electropositive hydrogen |
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What are two examples of electronegative atoms that can occur in hydrogen bonding? |
Oxygen and nitrogen |
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Can water form hydrogen bonds? |
Yes |
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What are the two components of a hydrogen bond? |
1. Hydrogen bond donor = H-A 2. Hydrogen bond acceptor = B |
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What are two key players in hydrogen bonding in biomolecules? |
1. Hydroxyl functional group 2. Amine groups |
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What happens to the orbitals in a covalent bond? |
The atoms are too close, their orbitals overlap |
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What happens to the orbitals in a hydrogen bond? |
When the orbitals are as close as possible without overlapping |
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What are Van-der Waals interactions? |
Electrostatic forces, involving dipoles, between molecules |
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What is the hydrophobic effect? |
The phenomenon by which nonpolar molecules aggregate to avoid contact with hydrophilic molecules, particularly water |
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What do nonpolar molecules tend to do in polar solvents? |
Aggregate |
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Is the hydrophobic effect favorable or unfavorable? |
Favorable |
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What is high entropy?
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Higher disorder of water |
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What is lower entropy? |
Lower disorder of water |
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Concerning nonpolar molecules in water, describe what is unfavorable? |
Many H2O molecules are ordered around the nonpolar molecules |
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Concerning nonpolar molecules in water, describe what is favorable? |
Fewer H2O molecules are ordered around the nonpolar molecules |
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T or F: Most lipids are not amphiphilic |
False |
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What are fatty acids? |
A type of lipid composed of a hydrophilic head group and a hydrophobic (nonpolar) hydrocarbon tail |
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What is an amphiphile? |
Molecule composed of a hydrophilic head group and a hydrophobic (nonpolar) hydrocarbon tail |
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What do amphiphilic molecules do in aqueous solutions? |
Form miscelles and lipid bilayers |
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How is a hydrophobic molecule classified? |
Nonpolar |
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How is a hydrophilic molecule classified? |
Polar |
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What is the symbol for the ionization constant for water? |
Kw |
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What is the known value of the ionization constant for water? |
Kw = [H+] x [OH-] = 10^-14 |
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What are the characteristics of pure water? |
[H+] = [OH-] = 10^-7 M = neutral |
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How is a solution in which [H+] > 10^-7 M classified? |
Acidic |
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How is a solution in which [H+] < 10^-7 M classified? |
Basic |
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What is the formula for calculating pH? |
pH = -log [H+] |
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What is the pH for a neutral reaction? |
7 |
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What is the pH for an acidic reaction? |
pH < 7 |
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What is the pH for a basic reaction? |
pH >7 |
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What type of relationship does [H+] and [OH-} have? |
An inverse relationship; as [H+] increases, [OH-] decreases |
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How is pH related to [H+]? |
Logarithmically proportional |
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When are pK and pH the same? |
At which the acid is half dissociated |
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What are the characteristics when the protonated form predominates? |
pH < pK |
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What are the characteristics when the deprotonated form predominates? |
pH > pK |
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How do pH and pK related to protonated and deprotonated forms? |
pH < pK = protonated pH > pK = deprotonated |
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When a pK is larger, what does this mean for an acid? |
It is a weak acid (less likely it will donate a proton) |
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What is the pH formula involving pK? |
pH = pK + log {[A-] / [HA]} |
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What is the structure of an amino acid when the pH < 3.5? |
COOH -- C -- NH3+ |
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What is the structure of an amino acid with 3.5 < pH < 9? |
COO- -- C -- NH3+ |
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What is the structure of an amino acid when the pH > 9? |
COO- -- C -- NH2 |
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What happens to an amino acid when the pH < 3.5? |
Amino acids have both protons and a net positive charge COOH and NH3+ |
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What happens to an amino acid when 3.5 < pH < 9? |
Amino acids lose the proton on the carboxyl carbon and zwitterions; charge is neutral COO- and NH3+ |
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What happens to an amino acid when pH > 9? |
Amino acids have lost bother protons and have a net negative charge COO- and NH2 |
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Is an acid a proton donor or acceptor? |
Proton donor |
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Is a base a proton donor or acceptor? |
Proton acceptor |
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How can the pH of a solution be altered? |
By adding a strong base/acid |
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What happens to the association of a strong acid/base? |
Completely dissociates |
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What happens to the association of a weak acid/base? |
Partially dissociates |
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What is a buffer?
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A solution containing a weak acid and its conjugate base |
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What are some weak acids commonly found in biological systems? |
Acetic acid Propionic acid Sorbic acid Benzoic acid Succinic acid |
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What is the Henderson-Hasselbalch equation? |
pH = pK + log { [A-] / [HA] } |
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When is the Henderson-Hasselbalch equation used? |
It can be used to figure out the ratio of acid to base forms of a buffer that are required to make the buffer at a given pH |
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When can the Henderson-Hasselbalch equation be used to determine the pH of a solution? |
When given the concentrations of HA and A- |
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What is a generic buffer equation? |
HA <----> H + A- |
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T or F: Buffer solutions can resist change in pH |
True |
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What is the rule of thumb for a buffer zone for when [A-] = 10 [HA]? |
pH = pK +log(10) = pK + 1 |
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What is the rule of thumb for a buffer zone for when [HA] = 10 [A-]? |
pH = pK + log(0.1) = pK - 1 |
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When do buffers tend to resist changes in pH? |
When [A-] and [HA] differ by no more than a factor of ten |
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What is a dipole? |
An interaction between two strongly polar groups |
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What is the strength of a dipole? |
About 9 kJ . mol-1 |
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What is the definition of electronegativity? |
A measure of an atom's affinity for electrons |
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Where on the periodic table is an element more electronegative? |
The top right |
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What is another word for "water loving"? |
Hydrophilic |
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What are examples of hydrophilic molecules? |
Glucose and other readily hydrated substances |
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What is another word for "water fearing"? |
Hydrophobic |
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T or F: Hydrophobic molecules are relatively soluble in water |
False |
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What is the difference in how micelles and lipid bilayers are formed by amphiphiles in aqueous solutions? |
Micelles are typically formed by lipids with ONE nonpolar tail Lipid bilayers are typically formed by lipids with TWO nonpolar tails |