LEARNING OBJECTIVE - water, pH, acid and bases

Difference between covalent bonds and noncovalent interactions

Covalent - are stronger and share electrons betweeen atoms of diffferent electronegativity, resulting in partial change seperation or polar bonds

Non covalent - dont share electrons and rely on weaker attractions or repulsion

3 types of non covalent interactions

1. Ion - ion: can be atoms that repulse (same) or attract (opposite charges)

2. Ion dipole: repulsive or attractive

3. Van der waal: involves dipoles, 3 types

Hydrogen bonds

Dipole dipole interactions in H2O

• A hydrogen atom bonded to a strong electroneg atom (donor) and another electronegative atom bearing a lone pair (acceptor)

3 types of van der waal

• dipole - dipole: 2 dipole that are attractive or repulsive

• Dipole - induced: dipole inducing dipole in a non polar molecule

• Dispersion forces: interaction between an instantaneous dipole and an induced dipole

Colligative properties of water

Are the physical properties of water that depend on the concentration of solutes

• solutes added to water elevates the boiling point and decreases the freezing point

How do water molecules form hydrogen bonds

They’re polar molecules with a bent shape that creates opposite electrical charges on each side. Partial charges on the hydrogen and oxygen cause hydrogen bonds to attract to surrounding molecules

• their polar bonds make permanent dipoles in the molecule

Mobility of protons in water

H+ is picked up by water to form a hydronium ion. Hydronium and hydroxide ion mobility is very fast.

• protons rapidly hop from one water molecule to the next

Hydrophilic vs hydrophobic

Hydrophilic - solvated by water (hydrated), polar

Hydrophobic - disrupts water H bond network, non polar

Hydrophobic effect

Tendency of water to minimize its contact with hydrophobic species, causing the species to aggregate in water (clump tgt)

Hydrophobic

Nonpolar molecules cluster together in water rather than mix individually

Solvated ions

Electrically charged atoms/molecuels surrounded and stabilized by a shell of oriented solvents

Hydrated ions

Individual positive or negative ions surrounded by a shell of. Oriented water molecules in an aq solution

• highly ordered

Water of hydration

Water molecuels chemically bound within a crystal structure to form a hydrate

Amphiphillic/amphiphatic

Has two distinct regions for a polar and non polar area

Micelles and bilayer

Clusters of amphiphillic molecules that form spontaneously in water

• hydrophobic tail inside and hydrophilic head outside

• both are specifically oriented in water

How do hydrophobic interactions contribute to formation of lipid bilayers

Amphiphatic phospholipids in water, non polar tails cluster together, increasing waters entropy thus bilayers assembles spontaneously

Bronsted Lowry acid and base definition

Acid - proton donor

Base - proton accepter

K vs Ka vs PKA

K - equilibrium constant, shows ratio of prod and react

Ka - specific K that measures how a weak acid dissociates in water

PKA - logarithmic acid dissociation constant

kw and Pkw

Kw - (H3O)(OH)

Pkw - log(Kw)

PH

Measures acidity and basicity

• 1-6 =acidic

• 8-14=basic

Monoprotic acid

1 acidic proton

Polyprotic acid

Has more than 1 acidic proton

Buffer

Weak acid and its conjugate base, neutralizes pH after addition of acid or base

• Weak acid neutralizes added base by converting it to a. Weak conjugate base

• Conjugate base absorbs excess protons when acid is added making it into a weak acid

Buffer capacity

How much a buffer can absorb before ph can no longer by resistant to change

Draw weak acid with strong base titration curve + weak base with strong acid titration curve

If given a table of buffers and their pKa, how do you identify the weak acid/base best to make a buffer for that pH

Find the one with the closest pKa to pH

How do scientists actually make a buffer irl

1M bottle of K2HPO4 and 1M KH2PO4. Mix fixed amounts of the two and dilute it to whatever concentration. Or use a pH meter