Acids, Bases, & pH
I. Macroscopic Properties
Easily Observable
Acids taste sour, bases taste bitter
B. Bases feel slippery (soap)
C. Acids & Bases react with each
other
A.
Acid-Base Indicators
Acids & Bases cause certain dyes to
change color. These dyes are called acidbase indicators.
E. . Example: Litmus changes red in acid &
blue when exposed to bases
F. Red cabbage, radishes & rose petals
D.
Macroscopic cont.
G. Reactions with metals & carbonates
1. Acids react with metals to form H2
**acids cause metals to corrode
2. Acids react with carbonates to form CO2
& water.
** This causes pollution & the wearing away
of limestone & marble.
II. Submicroscopic Properties
A. Acids and Bases
Acids have formulas that begin with an “H”.
They have an acidic hydrogen- a H atom that can be
transfered to water and is written 1st in a formula.
1 acidic H = monoprotic, ex: HCl
2 acidic H = diprotic, ex: H2SO4
More than 2 acidic hydrogen = polyprotic, ex: H3PO4
Acids are proton donors
Produce hydronium ions [H3O+]
A. Acids and Bases
The general reaction for an acid dissolving in
water is
Bases
often have formulas
that end in OH
Bases are proton acceptors
Bases produce hydroxide
ions [OH-]
A. The pH Scale
•Neutral pH = 7
[H3O+]=[OH-]
•Acids pH<7
[H3O+]>[OH-]
•Bases pH>7
[OH-]>[H3O+]
A. The pH Scale
Because the pH scale is a log scale based on 10,
the pH changes by 1 for every power of 10
change in the [H+].
B. Acid Strength
• Weak acid – most of the acid molecules remain intact
(HC2H3O2)
Common Acids
Strong acids
– Sulfuric acid, H2SO4
– Hydrochloric acid, found in gastric juice, HCl
– Nitric acid, HNO3
Weak acids
–Acetic Acid, found in vinegar, HC2H3O2,
–Carbonic Acid, found in soft drinks, H2CO3
–Phosphoric Acid, H3PO4
Acid Strength Continued
Weak does not mean insignificant!!
Ex: DNA = deoxyribonucleic acid
amino acids= building blocks of protein
B. Acid Strength Cont.
Strength vs. Concentration
An acid can be weak, but concentrated.
Ex: Pure ammonia is weak, but is
concentrated.
Add 1 gal of water to ammonia, it is
weak AND dilute
Concentration- the amount of substance
present in a unit volume
Common Bases
Strong bases are Group 1 or 2 metals
bonded with hydroxide.
ex: Sodium Hydroxide - NaOH
Potassium Hydroxide – KOH
Calcium Hydroxide - Ca(OH)2
Weak Bases
Household ammonia = Ammonium Hydroxide = NH4OH
Ammonia= NH3
C. Water as an Acid and a Base
Water is amphoteric – it can behave as either
an acid or as a base
Ionization of water
– Concentration of hydronium and hydroxide are equal
C. Water as an Acid and a Base
Product of [H3O+] and [OH−] is always
constant.
A. The pH Scale
The “p scale” is used to express small
numbers.
pH = −log [H+]
A. The pH Scale
A. The pH Scale
pOH
scale
pOH = −log [OH−]
pH + pOH = 14.00
A. The pH Scale
B. Measuring pH
Indicators – substances that exhibit
different colors in acidic and basic
solutions
– In an acid solution the indicator will be in the HIn form.
– In a basic solution the indicator will be in the In− form.
C. Calculating the pH of
Strong Acid Solutions
Determine the [H+].
pH = −log[H+]