Thursday, May 1st: “A” DayFriday, May 2nd: “B” Day

AgendaHomework questions/collectFinish section 15.2Section 15.2 workday:

Practice pg. 545: 1,2,4Sec. 15.2 review, pg. 547: #1-12

Next time:Quiz over section 15.2

Homework Questions?

Practice pg. 541: 1,2,4,5Practice pg. 544: 1-4

Measuring pHBecause of the negative sign, as the hydronium

ion concentration increases, the pH will decrease.

A solution of pH 0 is very acidic.

A solution of pH 14 is very basic (alkaline).

A solution of pH 7 is neutral.

pH values of some common materials

IndicatorsCertain dyes, known as indicators, turn

different colors in solutions of different pH.

An indicator is a compound that can reversibly change color depending on the pH of the solution or other chemical change.

pH MetersA pH meter is an electronic instrument equipped with

a probe that can be dipped into a solution.

The probe has two electrodes, one of which is sensitive to the hydronium ion.

An electrical voltage develops between the two electrodes, and the circuitry measures this voltage.

The instrument converts the measurement into a pH reading, which is displayed on the meter’s screen.

Indicators vs. pH MetersIndicators

Quick and convenientDo not give very precise results

pH MetersVery preciseMore complicated and expensive

or

Measuring pHWe know how to calculate the pH from the

[H3O+] or [OH-], but can we calculate the [H3O+] or [OH-], if we know the pH?

You bet your buttons we can!

Measuring pH

The pH equation may be rearranged to calculate the hydronium ion (H3O+) concentration from the pH.

[H3O+] = 10−pH

Sample Problem C, pg. 545Calculating [H3O+] and [OH-] from pH

What are the concentrations of the hydronium and hydroxide ions in a sample of rain water that has a pH of 5.05?

[H3O+] = 10−pH

[H3O+] = 10-5.05

[H3O+] = 8.91 X 10-6 MKw = [H3O+] [OH-] = 1.00 X 10-14

(8.91 X 10-6 M) [OH-] = 1.00 X 10-14

[OH-] = 1.12 X 10-9 M(3 sig figs)

Additional ExampleIf the pH of a solution is 8.1, what is [H3O+] in the

solution? What is the [OH-] in the solution?[H3O+] = 10−pH

[H3O+] = 10 –8.1

[H3O+] = 7.9 X 10-9 MKw = [H3O+] [OH-] = 1.00 X 10-14

(7.9 X 10 -9) [OH-] = 1.00 X 10-14

[OH-] = 1.3 X 10-6 M(2 sig figs)

Section 15.2 WorkdayPractice pg. 545: #1,2,4Section 15.2 review: Pg. 547: #1-12Section 15.2 concept review: “Acidity, Basicity,

and pH”

Next time…Quiz over section 15.2