Ch. 2 Water (Exam 1) Flashcards
Covalent Bonds, Hydrogen Bonds (Non-Covalent), Hydrophobic Effect, Acids, Base, pH
How would the electronegativity of a nonpolar covalent bond be described?
Not a big difference in EN
How would the electronegativity of a polar covalent bond be described?
A significant difference in EN
How polar is an ionic bond, and how would its electronegativity be described?
Extremely polar w/ enormous difference in EN
What is electronegativity?
The measure of an atom’s attraction for electrons it shares w/ another atom
What is the periodic table trend for electronegativity?
Up and to the right (EN gets stronger)
Which type of bonds are most important for biomolecules?
Polar bonds
Why do some molecules have polar bonds but are considered nonpolar overall?
Their geometry makes it so that the net vector sum of their dipole moments equals zero
What shape is water’s molecular geometry?
Bent
What shape is water’s electron-pair geometry?
Tetrahedral
Why is liquid water denser than ice?
The molecules in liquid water move more closely together, so they are not optimally/maximally hydrogen-bonded (bonds not set in stone)
How do hydrogen bonds affect water’s boiling point?
The cohesiveness created by the H-bonds help water molecules resist the need to escape to the gas phase
How do the molecular weight, melting point, and boiling point of non-water hydrides relate to each other?
They are all directly proportional
Why does a greater frequency of hydrogen bonds allow for ice to float on water?
More frequent, optimal, set-in-stone H-bonds equals less free-floating molecules and less volume by creating hollow regions between the H-bonds that make ice less dense than water
Why is hydrogen bonding important for biomolecules?
Hydrogen bonding stabilizes the 3D structures of biomolecules
What are the 3 major types of hydrogen bonds found amongst biomolecules?
1) Water to water
2) Water to other polar molecules (w/ carbonyls)
3) Bonds in proteins and nucleic acids
What are 2 reasons that oil and water do not mix?
1) Nonpolar molecules separate themselves from polar water
2) Water forms H-bonds w/ itself and other polar molecules
What 2 regions do amphipathic compounds consist of?
Hydrophobic and hydrophilic regions
What is a micelle?
A spherical cluster of amphipathic molecules in water with hydrophobic parts inside the sphere and hydrophilic parts outside with water
How can solute molecules dissolve in water if H-bonds between water molecules are so extensive?
A stronger interaction than hydrogen bonding exists between solute and water
What are 2 compounds that can dissolve fairly easy in water?
Ionic and polar covalent compounds
How do ionic compounds dissolve in water?
Cations interact with oxygen, and anions interact with hydrogens in a process called hydration
How do uncharged polar molecules interact w/ water molecules?
Hydrogen bonding
What does pure water produce when it dissociates?
Equal amounts of protons and hydroxide ions
What does an acid increase in a solution?
Proton concentration
What does a base decrease in a solution?
Proton concentration
What is the dissociative difference between weak and strong acids?
Weak acids partially dissociate in water while strong acids completely dissociate
What is the dissociative difference between weak and strong bases?
The same thing as weak and strong acids (weak partially dissociates in water while strong fully dissociates)
Neutral solutions contain equal concentrations of what?
Acids and bases
What is the physiological pH range?
2-8
What is the formula for calculating pH based on proton concentration?
pH = -log[H+]
What does pKa express?
The strength of a weak acid
What does a lower pKa mean for an acid?
Lower pKa = stronger acid
What formula determines pKa?
pKa = -log Ka
What is the acid dissociation constant?
Ka
What does a titration curve measure?
pH and acid concentration
What is the buffering region, and what does it correspond to?
Area on a titration curve where little pH change occurs, and it corresponds to pKa value
What is a buffer?
A solution that resists change in pH when acids or bases are added
How are buffers made?
Combination of a weak acid and conjugate base
When does the best buffering occur?
1 pH unit above and below pKa
What relationship does the Henderson-Hasselback equation establish when selecting a buffer?
The relationship between pH and pKa
What is the formula for the Henderson-Hasselback equation?
pH = pKa + log([A-]/[HA])
What is special about each of the ionizable groups of weak acids?
Each ionizable group has its own pKa
How are the protons of a weak acid released on a titration curve?
Stepwise
