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Modern Chemistry Chapter 15 Acid-Base Titration & pH

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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 so

14 – 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 base

Ma = molarity of acid Mb = molarity of base

eqa = #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

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