Definitions

Examples and types of acids and bases

Properties

pH and pOH

Neutralization

AcidAcidAnything that produces hydrogen ions in a water solution.

HCl (aq) H+ + Cl-

BaseBaseAnything that produces hydroxide ions in a water solution.

NaOH (aq) Na+ +

OH-

Arrhenius Definition

Arrhenius definition islimited to aqueous solutions.

There are many definitions, but the most convenient for

this course is this one.

AcidAcidA proton donor

NaOH + HCl (aq) NaCl + H2O

BaseBaseA proton acceptor

HCL + NaOH (aq) NaCl + H2O

BrØnsted-Lowry Definition

Examples and types of acids

ACID FORMULA COMMON NAME

(Inorganic or mineral)Nitric HNO3aqua fortisHydrochloric HCl muriatic acidSulfuric H2SO4 oil of vitriolcarbonic H2CO3 carbonated water

(Organic)Formic HCOOH ------Acetic HC2H3O2 vinegar

Examples and types of bases

BASE FORMULA

Sodium hydroxide NaOHPotassium hydroxide KOHAmmonium hydroxide NH4OHCalcium hydroxide Ca(OH)2

Magnesium hydroxide Mg(OH)2

Magnesium and calcium hydroxideare used as antiacids.

Magnesium hydroxide is known as Milk of Magnesia.

General properties of acids

1. Acids react with active metals to produce hydrogen gas.

Zn(s) + 2HCl(aq) ZnCl2 + H2

Question: How can you test for hydrogen?

2. Acids affect the colors of acid-base indicators.

3. Acids and bases are electrolytes.

4. Acids neutralize bases.

5. Dilute acids have sour taste. (Citrus fruits, vinegar and sour milk taste sour because of the presence of dilute acids). Some acids are poisonous.

The pH and/or pOH is a measure of the acidity or alkalinity of an aqueous solution.

0

7

14

Increasing acidity

Neutral

Increasing basicity

pH

0

7

14Increasing basicity Increasing acidity

pOH

The pH-meter is a device used to find the pH of a

solution.

pH indicators: Organic substance that changes color according to the pH.

Dissociation constant, Ka/Kb

HAc H+ + Ac Ka = ####

The pH depends on the hydrogen ions concentration [H+] and this concentration

depends on the dissociation constant Ka or Kb.

Strong acids/bases are highly or completely dissociated.

Weak acids are just partially dissociated.The higher Ka the higher the [H+].

IONIZATION OF ACIDS

ACID Ionization equation Ionization constant, Ka

hydrochloric HCl ---> H+ + Cl- Very large

nitric HNO3 ---> H+ + NO3- Very large

sulfuric H2SO4 ---> H+ + HSO4- Large

acetic HC2H3O2 <=> H+ + C2H3O2- 1.8x10-5

hydrosulfuric H2S <===> H+ + HS- 9.5x10-8

hydrofluoric HF <===> H+ + F- 3.5x10-4

pH calculations

Pure water is neutral (pH = 7) because the hydrogen ions concentration equals the hydroxide ions

concentration.

[H+] = [OH-] = 1.0 x 10-7 M

From this equation we can say that

[H+]x[OH-] = 1.0 x 10-14 (1)

By using logarithms, we obtain the followingequations:

pH + pOH = 14 (2)

pH = -log [H+] (3)

pOH = -log [OH-] (4)

Given the pH/pOH how do you solve for[H+] and/or [OH-]????? (5) and (6)

Both the hydrogen ions concentration, [H+], and the hydroxide ions concentration, [OH-], are expressed in Molarity (moles per liter of solution).

For a strong acid, the molar concentration (M) is the same [H+] , for a base, the molar concentration is the same [OH-].

Thus, 0.01 M, HCl has [H+] = 0.01 M

0.0001 M, NaOH has [OH-] = 0.0001 M

pH scale works only for concentrations below 1 M.

Exercise:

What is the pH of 1.3 x10-3 M, HCl solution?

Answer:

pH = -log [H+], then

pH = -log [1.3x10-3]

pH = 2.88

A neutralization is a chemical reaction in which an acid is neutralized by a base or viceversa to produce salt and water. In this reaction the hydrogen ions from the acid react with the hydroxide ions from the base to produce water. The point at which the neutralization finishes is called the EQUIVALENCE POINT.

NEUTRALIZATION