Acids & Bases (Stillwagon Unit 10)

Arrhenius acids & bases

Arrhenius acids & bases

acids: give off hydrogen in water

bases: give off hydroxide in water

bronsted lowry acids and bases

acids: give off hydrogen ions

bases: can gain hydrogen ions

water is not involved in relationship

amphoteric susbtance

substance with the ability to lose or gain a hydrogen

conjugate acids

product that is formed when base gains a hydrogen (weak bases produce strong conjugate acids and vise versa)

conjugate bases

product that is formed when acid loses a hydrogen (weak acids produce strong conjugate bases and vise versa)

ion product constant (K or Kw)

K = [H][OH]

At 25ºC, Kw = 1.0 × 10^-14

calculating pH & H

pH = -log [H]

H = 10^-pH

manipulating equations if given [OH]

pOH = -log [OH]

[H] = Kw/[OH]

ionization

substance splits into ions when dissolved in water

strong acids

• complete ionization (only forward reaction)

• contains weak conjugate base

what are the strong acids & bases

12 (or 13) strong acids/bases

weak acid

• does not fully dissociate when dissolved in H2O (reversible reaction)

• [H2O] considered constant, not included in equation

acid dissociation constant (K_a)

extent of proton transfer determines strength of acid

• smaller K_a → less ionizable acid

• can solve for acid/base using same process for equillibriums

• pK_a = -log(K_a) or K_a = 10^-pKa

K_a equation

Keq * [H2O] = [H3O][A]/[HA] (products/reactants)

if [HA]/Ka > 500…

change in initial concentration of x is negligible (can remove x from E row)

if [HA]/Ka < 500…

change in initial concentration of x is not negligible (must keep x in the E row)

solving Ka/Kb steps:

given: (M and pH)

solving for: Ka/Kb

1. is it a strong acid? if not, make ICE table

2. create ICE table & Ka equation

3. use pH to find [H]

4. plug in [H] for x in Ka equation

solving for [OH] & pH steps:

given: Ka/Kb, M

solving for: ([OH] and pH)

1. check to see if [B]/Kb > 500

2. create ICE table & Kb equation

3. use Kb equation to find Kb using algebra

4. use [OH] to find pH

pH scale

shows relationship between pH and hydrogen ions concentration

acid/base indicators

most have ~ 1.5 ph range and are useful only for specific measurements

universal indicator

goes from ph ranges 1-12 in rainbow order, not very specific

neutralization

when an acid and a base react in a solution and the acidity of the acid and the alkalinity of the base neutralize each other. produces water (HOH) and a salt (ionic compund)

neutralization formula steps

combine cation from base and anion from acid + HOH to make formulas for products

neutralization problem

given: V & M of one substance

V of another

Solve for M using train tracks

titration

the process of adding one solution of a known concentration to another to determine the concentration of the other solution

solution of known concentration

standard solution

end point

point at which indicator changes color in titration

buret

a graduated glass tube with a tap at one end, for delivering known volumes of a liquid, especially in titrations.

titrant

a substance added in titration

analyte

a substance whose chemical constituents are being identified and measured through the addition of another substance to it (titration)