Transcript Section 15.2 Day 2

Thursday, May 1st: “A” Day
Friday, May 2nd: “B” Day
Agenda
 Homework questions/collect
 Finish section 15.2
 Section 15.2 workday:
Practice pg. 545: 1,2,4
Sec. 15.2 review, pg. 547: #1-12
Next time:
Quiz over section 15.2
Homework Questions?
Practice pg. 541: 1,2,4,5
Practice pg. 544: 1-4
Measuring pH
Because 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
Indicators
Certain 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 Meters
A 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 Meters
Indicators
Quick and convenient
Do not give very precise results
pH Meters
Very precise
More complicated and expensive
or
Measuring pH
We 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. 545
Calculating [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 M
Kw = [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 Example
If 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 M
Kw = [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 Workday
Practice pg. 545: #1,2,4
Section 15.2 review: Pg. 547: #1-12
 Section 15.2 concept review: “Acidity, Basicity,
and pH”
Next time…
 Quiz over section 15.2