Ch 12: Acid Base

Strong Acids

Strong Acids

HCl, HNO3, H2SO4

Weak Acids

CH3COOH, any not listed in strong acids

Strong Bases

Group I hydroxides, Group II hydroxides (except Be and Mg)

(ex. NaOH)

Weak Base

NH3

True or False: acids react with active metals to produce hydrogen gas

true

True or false: acids react with bases to produce salts

true

definition of acids and bases in the Brønsted–Lowry

an acid is a proton (H⁺) donor, and a base is a proton acceptor

Conjugate pairs

an acid base pair that differs by one proton (the acid has one more than the base)

ex. HCl, conj. Cl-

Stong v Weak re disassociation

strong - disassociate 100%

weak - disassociate less than 1% (no real set number)

Can you titrate a weak acid with a weak base

no

Monoprotic

acid that can donate one proton (H+)

ex. HCl

Polyprotic

acid that can donate more than one proton

ex. H2SO4, H3PO4

Amphiprotic

can donate and accept protons, normally neutral ish pH

Ex. H2O

Does water dissociate

yes, sparingly, can write equilibrium equation

relationship between pH and pOH (equation)

pH + pOH = 14

Kw equation

[H+] * [OH-] = 1.0 x 10ˆ-14

if Kw is small it will dissociate a lot/very little

very little

Calculating pH equations

pH = -log[H+]

[H+] = 10ˆ(-pH)

Calculating pOH equations

pOH = -log[OH-]

[OH-] = 10ˆ(-pOH)

equilibrium weak acids

weak acids dissociate a very small amount. equilibrium equation is written since it happens so sparingly

Equi expression: Ka = ([A-][H3O+]) / [HA]

What is HA

generic acid formula (no A element)

Steps for calculating Ka of weak acids (can only do for weak acids because they are two way)

1. write the dissociation equation for weak acid

2. set up ICE box

3. plug in [weak acid] in the “I” row under the weak acid

4. plug in zeroes in the “I” row under the H3O+ and conjugate base (A-)

5. Calculate the [H3O+], if not given

   1. use the equation [H3O+] = 10ˆ(-pH)

6. Plug in the [H3O+] in the E row under H3O+

7. Solve ICE box

   1. the change under HA is negligible, don’t bother subtract it

8. Solve for Ka

Bromothymol Blue (BTB)

yellow 6-8 blue (SA/SB)

Methyl Orange

red 4-6 yellow (SA/WB)

Phenolphthalein

colorless 8-10 pink (WA/SB)

pH curve SA/SB

Starts at ~1, equi point at ~7, ends at ~13??

pH curve WA/SB

Moves up by the same amount, ±2

start ~3, equi ~9, ends at ~13??

pH curve WB/SA

Moves down by same amount, ±2

start ~11, equi ~5, end ~1

Buffers

buffers are solutions that resist changes to pH when an acid or base is added

how to make a buffer (2 ways)

1. mix a weak acid with is salt form conj. base

2. partial neutralization (AP chem): make a buffer by partially neutralizing a weak acid