the ph scale & ph calculations chemistry 10 mrs. page
TRANSCRIPT
The pH Scale & pH Calculations
Chemistry 10 Mrs. Page
Learning Objectives:• Explain and use the pH scale• Use a pH meter and universal
indicators to determine the acidity or alkalinity of a substance
• Solve problems involving pH and [H+]
The pH Scale• pH is a measure of how acidic or basic
a solution is, which means it is a measure of the concentration of hydrogen ions [H+] in a solution.
• The pH scale ranges from 0 to 14. • Acidic solutions have pH values below
7• A solution with a pH of 7 is neutral
(pure water)• Basic/alkali solutions have pH values
above 7.
Explain and use the pH scale
pH Scale• The pH scale is a way of
expressing the amount of dissociation of acids and bases in water.
• Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ions.
Explain and use the pH scale
pH Scale• The pH scale is a logarithmic scale (not linear).• A change of 1 pH unit represents a tenfold change in
the acidity of the solution. • For example, if one solution has a pH of 1 and a
second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.
Explain and use the pH scale
Measuring pH• Indicators are substances that turn different
colors in the presence of an acid or base
•Universal Indicator – color indicates pH
•Litmus paper – turns red acid, turns blue base
Use a pH meter and universal indicators to determine the acidity or alkalinity of a substance
Measuring pH• Indicators are substances that turn different
colors in the presence of an acid or base
•Phenolphthalein: commonly used in titrations, turns pink in basic solutions
•Methyl orange: commonly used in titrations, turns orange in acidic solutions
Use a pH meter and universal indicators to determine the acidity or alkalinity of a substance
Measuring pH• pH Sensor: digital tool
for measuring pH• Must be used with a
GoPro and Logger Pro software
• Gives reading as a pH number
Use a pH meter and universal indicators to determine the acidity or alkalinity of a substance
pH CalculationsSolve problems involving pH and [H+]
pH = - log [H+](Remember that the [ ] mean Molarity)
Calculate the pH of a solution if the [H+] is 1 X 10-10
pH = -log [H+] = -log (1 x 10-10)
pH = 10CAREFUL: on you calculator use (-) for negative & use () around numbers
pH CalculationsSolve problems involving pH and [H+]
pH = - log [H+](Remember that the [ ] mean Molarity)
Calculate the pH of a solution if the [H+] is 1.8 X 10-5
pH = -log [H+] = -log (1.8 x 10-5)
pH = 4.7
pH CalculationsSolve problems involving pH and [H+]
pH = - log [H+](Remember that the [ ] mean Molarity)
Find the pH of a 0.15 M solution of Hydrochloric acid
pH = -log [H+] = -log (0.15)
pH = 0.82
pH CalculationsSolve problems involving pH and [H+]
pH = - log [H+](Remember that the [ ] mean Molarity)
Find the pH of a 3.00 X 10-7 M solution of Nitric acid
pH = -log [H+] = -log (3.00 x 10-7)
pH = 6.52
pH CalculationsSolve problems involving pH and [H+]
pH = - log [H+]If you have pH you can also calculate the [H+]
-pH = log [H+]
Take antilog (10x) of both sides and get
10-pH = [H+]* to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button
pH CalculationsSolve problems involving pH and [H+]
If the pH of Coke is 3.12, what is the [H+] ?
10-pH = [H+]
10-3.12 = [H+]
[H+] = 7.59 x 10-4M
pH CalculationsSolve problems involving pH and [H+]
A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?
10-pH = [H+]10-13.4 = [H+]
[H+] = 3.2 x 10-9M
pH CalculationsSolve problems involving pH and [H+]
A solution has a pH of 1.5. What is the Molarity of hydrogen ions in the solution?
10-pH = [H+]10-8.5 = [H+]
[H+] = 0.032M