Water, Acids and Buffers Flashcards
Chemical bonding of water
2 electron pairs covalently linked to 2 hydrogen atoms.
Hydrogen bonds
Strong dipole-dipole interactions between a covalently bound hydrogen and a lone pair of electrons. Weak compared to covalent bonds
How many H-bonds per water molecule?
- In liquid water, it is an average of 3.4.
Adhesion
Binding between unlike molecules.
Cohesion
Binding between like molecules. Results in high surface tension.
Ionic interactions
Electrostatic interactions between charged species, between the ion and dipole, or between uncharged but polar molecules.
van der Waal interactions
Weak interactions between all atoms regardless of polarity.
Hydrophobic effect
Ordering water molecules around non polar substances.
Why do hydrophobic solutes have low solubility?
Water surrounding nonpolar solutes has a low entropy, low entropy is thermodynamically unfavorable.
Miscelles
Clusters of nonpolar molecules with the hydrophobic tails facing inwards.
What allows for proton hopping?
Covalent and hydrogen bonds are interchangable, which allows for fast mobility of protons in water.
The stronger the acid…
The lower its pKa, the more it will dissociate.
A conjugate acid-base pair can…
Act as a buffer.
At the midpoint of a titration curve…
pH=pKa. The buffering capacity is at its greatest.
Buffering capacity is lost when…
The pH differs from pKa by more than 1 pH unit.
