Acids, Bases, & pH

I. Macroscopic Properties

Easily Observable

A. Acids taste sour, bases taste bitter

B. Bases feel slippery (soap)

C. Acids & Bases react with each

other

Acid-Base Indicators

D. Acids & Bases cause certain dyes to change color. These dyes are called acid-base indicators.

E. . Example: Litmus changes red in acid & blue when exposed to bases

F. Red cabbage, radishes & rose petals

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 AcidsStrong 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 - NaOHPotassium Hydroxide – KOHCalcium Hydroxide - Ca(OH)2

� Weak BasesHousehold 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+]