Modern Chemistry Chapter 15Acid-Base Titration & pH

Section 1

• self-ionization of water occurs when two water molecules produce a hydronium (H3O+) and a hydroxide (OH-) ion

2 H2O H3O+ + OH-

• The ionization constant (Kw) of water is: Kw = [H3O+] [OH-] = 1.0 x 10-14 M

Acidic, Basic, & Neutral

• IF [H3O+] > [OH-] then solution is acidic.

• IF [H3O+] < [OH-] then solution is basic.

• IF [H3O+] = [OH-] then solution is neutral.

Calculating [H3O+] & [OH-]

• Since the product of the hydronium and hydroxide ion concentrations is a constant, we can use the following formula to determine these concentrations.

[H3O+] [OH-] = 1.0 x 10-14 M

Use this formula to answer problems #1-4 on page 502 of the textbook.

The pH Scale

• The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration, [H3O+].

pH = -log [H3O+]

• The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration, [OH-].

pOH = -log [OH-]

pH & pOH

pH + pOH = 14 so14 – pH = pOH and 14 – pOH = pH

See figure 3 on page on page 503.See table 3 on page 504.See table 4 on page 504.

Do problem #1 on page 505.Do problems #1-4 on page 506.Do problems #1-4 on page 508.

Cross-Disciplinary Connection

• Read the Cross-Disciplinary Connection titled “Liming Streams” on page 510.

• Answer both questions at the end of the article.

Section 2Determining pH and Titrations

• acid-base indicators are compounds whose colors are sensitive to pH

• transition interval is the pH range over which an indicator changes color

• a pH meter determines the pH of a solution by measuring the voltage between two electrodes placed in a solution.

Titration

• titration is the controlled addition and measurement of the amount of a solution of a known concentration required to react completely with a measured amount of solution of an unknown concentration

• equivalence point is the point at which the two solutions used in a titration are present in chemically equivalent amounts

• endpoint is the point in a titration at which the indicator changes color

• standard solution is the solution that contains a precisely known concentration of solute

Titration

• see figure 10 on pages 518-519 for the steps of a titration

• A general equation for the solution of titration problems would be

VaMaeqa = VbMbeqb

Va = volume of acid Vb = volume of baseMa = molarity of acid Mb = molarity of baseeqa = #H in formula of acid eqb = #OH in formula of base

Titration

• Do practice problems #1-2 on page 521.

• Do section review problems #1-2 on page 521.

• Do chapter review problems #6, 8, 9, 12, 13, 24, 25, & 26 on pages 523-524.

Modern Chemistry Chapter 15Test Review

• 25 multiple choice– definition of self-ionization– [H3O+] [OH-] = 1 x 10-14

– definition and formula for calculating pH = -log[H3O+]– pH >7 is a base; pH <7 is an acid; pH = 7 is neutral– pH range is normally 0 to 14– calculate pH from [H3O+] – calculate [H3O+] from pH– definitions of indicators, transition interval, titration,

neutralization, endpoint, standard solution– acid-base titration monitors pH– titration problems using VaMaeqa = VbMbeqb