1. Acids and Bases
Let’s start with a review of some things you may already know about Acids and Bases!

2. Characteristics of Acids
Tastes Sour
Conduct Electricity
Some acids react strongly with metals
Turns blue litmus paper red
Corrosive, which means they break down certain substances.

3. Examples of Acids Acetic Acid = Vinegar
Citric Acid = lemons, limes, & oranges. It is in many sour candies.
Ascorbic acid = Vitamin C which your body needs to function.
Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics, car batteries

4. Back to Basics! Bases have a bitter taste. Conduct Electricity
Turns Red litmus paper Blue
Bases are usually slippery and give give soaps, ammonia, other cleaning products some of their properties.
Your blood is a basic solution.

5. Examples of Bases
Magnesium Hydroxide = Milk of Magnesia – Help for upset stomach
Drain Cleaner = Unclogs pipes
Sodium Bicarbonate – Baking Soda = Useful for cooking and cleaning

6. pH Scale and all it’s glory!

7. pH Scale pH is a measure of how acidic or basic a solution is.
The pH scale ranges from 0 to 14.
Acidic solutions have pH values below 7, Basic solutions have pH values above 7.
A solution with a pH of 7 is neutral, such as pure water.

8. What is it really measuring…
pH is a measurement of the H+ ion concentration. The greater the H+ ions in a solution, the more acidic, and lower the number on the pH scale.
The actual concentrations are very small so a logarithmic scale is used, based on a power of ten!
If a 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.

9. Calculating the pH of Strong Acids
To determine the pH of a strong acid, you first need the Hydrogen ion concentration. Remember that in a strong acid, all the molecules dissociate into the hydrogen ions.
This is expressed in Molarity and abbreviated in brackets. Ex [H+] = 2.05 M
To determine the pH:
pH = - log [H+]

10. Significant Digits * One Sig Fig so One Decimal pH = −log [1 x 10−4 ]
Significant digits in pH calculations are tricky because of the logarithmic scale.
The number of decimal places in the pH is determined by the significant figures in the coefficient.
Example: For a solution with [H+] = 1 x 10−4
pH = −log [1 x 10−4 ]
pH = - [-4.0]
pH = 4.0
* One Sig Fig
so One Decimal

11. Significant Digits Examples:
[H3O+] = 1 x 10-4 pH = 4.0 [H3O+] = 8.0 x 10-6 pH = 5.10 [H3O+] = 2.45 x 10-8 pH = 7.611

12. Practice: Calculate the pH
Find the pH of these strong acids: pH = - log [H+]
1) A 0.15 M solution of Hydrochloric acid
Ans: pH = 0.82 – 2 sig figs = 2 decimal places.
2) A 3.00 X 10-7 M solution of Nitric Acid
Ans: pH = – 3 sig figs = 3 decimal places

13. Calculating the [H+] pH = - log [H+] How do you get [H+] by itself?
Suppose you know the pH, but want to solve for the [H+] concentration?
A strong acid has a pH of Determine the [H+] concentration.
pH = - log [H+]
How do you get [H+] by itself?
First need to divide by -1….

14. [H+] = 10-3.12 = 7.6 x 10-4 M Calculating the [H+] -pH = log [H+]
Take antilog (10x) of both sides and get rid of the log. 10-pH = [H+] So….
[H+] = = 7.6 x 10-4 M
* Remember: pH has 2 decimal places, so coefficient can only have 2 significant digits:

15. You Try! Practice Problem
A solution has a pH of What is the concentration of hydrogen ions in the solution?
pH=-log [H+]
1.25=-log [H+]
-1.25=log [H+]
= [H+]
0.056= [H+]

16. Practice Problems:
1) Determine the pH of a solution that has a hydrogen ion concentration of 5.0 x 10-2.
pH = - log [5.0 x 10-2] = pH = 1.30
* 2 SF in base = 2 decimal places
2) Human blood must maintain a pH range of to Determine the range of [H+] for blood.
7.35 = - log [H+] = 4.5 x 10-8 M
7.45 = - log [H+] = 3.5 x 10-8 M

17. Determining the pOH of Strong Bases:
Determining the pH is a useful calculation, but is limited to acids because acids give of the H+ ion.
If we want to consider bases, we need to consider the concentration of [OH-] ions instead of [H+] ions.
This can be done by solving for the pOH:
pOH = - log [OH-]
It’s the same exact thing, except this time it’s the hydroxide ion concentration!

18. pH + pOH = ???
There is a relationship between the pH and pOH that is important to know, and water can help us.
What do we know about the pH of water?
Water is right in the middle of the pH scale because it has the exact same [H+] and [OH-] concentrations. They are…
[H+] = 1.0 x 10-7
[OH-] = 1.0 x 10-7

19. pH + pOH = ???
Converting both of these to their respecteive pH and pOH by taking their negative log:
- pH = 7 & pOH = 7
Again, right in the middle of the scale. So what is the sum of pH and pOH going to be?
14!!! – This will always be true of ANY substance and can be helpful in determining calculations. *See auto-ionization of water

20. Using pOH to get [H+]
What is the hydrogen ion concentration of a M NaOH solution?
* Note we cannot simply take the –log because it’s not an acid. We must use the pOH.
pOH = -log[OH-]  pOH = -log[0.0010] = 3
But we want the [H+] so pH + pOH = ????

21. Using pOH to get [H+] pH + pOH = 14 pH = 14 – pOH  pH = 14 – 3 = 11
Note: This makes sense because 11 is a base on the pH scale and NaOH is a base b/c of the hydroxide ion.
Almost there: pH = -log[H+]
11 = -log[H+]
[H+] = 1.00 X 10-11

22. Problem
The pH of a sample of human blood was measured to be 7.41 at 25 °C. Calculate pOH, [H+], and [OH-] for the sample.

23. Practice Problems:
A chemist dilutes concentrated hydrochloric acid to a 3.0 M. Calculate the [H3O+], pH, [OH-], and pOH of the solution at 25°C.

24. Practice Problems:
Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral?