Chem 161: Ch18

exam three

monoprotic acid

an acid that can donate a single proton

polyprotic acid

an acid that can donate more than one proton

nonmetal hydrides

smaller atoms have the valence electrons present in a smaller space. higher electron density results in stronger bonds = weaker acids

electronegativity

if the size is about the same then the acidity increases with increasing electronegativity of atom bonded to hydrogen

oxyacids - H atom is bonded to an O atom

• the acidity increases with increasing electronegativity of atom bonded to the oxygen-hydrogen

• for the same central, the higher the oxidation state (the more O’s attached) then the stronger the acid, greater shift of electrons away from the O attached to the H

salt solution: neutral

-salt consisting of the anion of the anion of a strong acid and the cation of a strong base yields a neutral solution

ex: NaNo3

salt solutions: acidic

-a sat consisting of the anion of a strong acid and the cation of a weak base yields an acidic solution because the cation acts as a weak acid

• NH4Cl

-a salt consisting of a cation of a strong base and an anion of a polyprotic acid that still has an H+ yields an acidic solution

• NaN2PO4

Salt Solutions: Basic

-a salt consisting of the anion of a weak acid and the cation of a strong base yiqlds a basic solution because the anion acts as a weak base

• NaC2H3O2

Buffer solutions

solutions that do not change pH when linited amounts of acids or bases are added

Buffer

-prepared by using a weak acid or base and a salt of the acid or base in approximately equal concentrations

-must have an acid that can react with any added base and a base that can react with any added acid

Common-Ion Effect

occurs when a reactant containing a given ion is added at an equilibrium mixture that already contains that ion and the position of equilibrium shifts away from forming more of it

pK_a =

-log (K_a)

Henderson-Hasselbalch Equation

• pH = pK_a + log [Base/acid]

• [H+] = K_a [acid/base]

Preparing a Buffer

1. choose a conjugate acid/base pair with a pK_a close to the desired pH

2. calculate the ratio of buffer components

3. determine the buffer concentration

4. adjust pH

Buffer capacity

a solution is the amount of acid or base that can be added to the buffer without a significant change in pH

• the more concentrated the buffer the greater buffer capacity

Herdersib-Hasselbalch Equation

pH= pK_a + log[base/acid]

[H+] = K_a [acid/base]

Titration

measures the volume of a standard solution of known concentration required to react with a measure amount of sample

Equivalence point

the point at which the reaction is complete- equivalent quantites of acid and base have reacted

acid-base indicator

-will change colorsat the equivalence point

-derived from weak organic acids

End point

-is where the color changes

-the end point and the equivalence point to be the same

Titration Curves for Polyprotic Acids

-have more than one K_a value

-each acidic H has a K_a and each needs to be tirated

Lewis base

is any species that donates an electron pair

Lewis acid

is any species that accepts an electron pair

adduct

-the product of any Lewis acid-base reaction

-is a single species that contains a new covalent bond