1. Mixing Acids and Bases
All your base... 1 1 1 1 1 1 1 1

2. Only One Question 1. What happens when you mix an acid and a base?
Actually, it's very visually unimpressive 2 2 2 2 2 2 2 2

3. Only One Question 1. What happens when you mix an acid and a base?
You have probably been told that they neutralize
You may also have heard the line “you get water and salt” 3 3 3 3 3 3 3 3

4. Only One Question 1. What happens when you mix an acid and a base?
You have probably been told that they neutralize
Partially correct. It depends on the amounts
You may also have heard the line “you get water and salt”
True if your base is hydroxide, and also you get a salt (aka ionic compound), not necessarily NaCl 4 4 4 4 4 4 4 4

5. The Actual Reaction
Definition of an acid-base reaction: an H+ transfers from an acid onto something else (the base):
Generically: HA + B- → HB + A-
Let's start with a specific example:
HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)
Of course, the net ionic equation is much simpler
H+ (aq) + OH- (aq) → H2O (l) 5 5 5 5 5 5 5 5

6. The Actual Reaction
So when we're done, the reaction has made water. Neutral, right...?
H+ (aq) + OH- (aq) → H2O (l)
...well, only if water is the only thing in there.
What if we didn't use equal amounts? Then there will be either some acid or base left, and it won't be neutral anymore. 6 6 6 6 6 6 6 6

7. Example Calculation 70 mL of 0.1 M HCl mixed with 30 mL of 0.2 M NaOH
H+ (aq) + OH- (aq) → H2O (l)
*Obviously there's all this other water there. This is just counting the reaction
So when we're done, there are moles of H+ left in a new volume of 100mL, which works out to be 0.04M.
pH = -log(0.04) = 1.4
Definitely not neutral—we would need to add more base
Moles before
0.007
0.003 0*
used/made
Moles after
0.004
0.003* 7 7 7 7 7 7 7 7

8. Titration
In fact, there's a method for finding the amount of acid or base in something that uses this fact: you put acid in a container, add add base until it's neutralized. This is a titration.
When it's neutralized, you know the moles are equal. 8 8 8 8 8 8 8 8

9. Titration
In fact, there's a method for finding the amount of acid or base in something that uses this fact: you put acid in a container, add add base until it's neutralized.
When it's neutralized, you know the moles are equal.
If you track the pH along the way,
you get a graph like this. 9 9 9 9 9 9 9 9

10. Titration
In fact, there's a method for finding the amount of acid or base in something that uses this fact: you put acid in a container, add add base until it's neutralized.
When it's neutralized, you know the moles are equal.
If you track the pH along the way,
you get a graph like this.
However, it's more typical to add
an indicator—something that changes
colors when you get to the right point 10 10 10 10 10 10 10 10

11. Titration Setup The setup for a titration looks something like this:
usually base in here, dripped in slowly
acid and indicator in here 11 11 11 11 11 11 11 11

12. Titration Setup
When you get to the equivalence point (neutralized), it changes color:
If I know how much of this I used, and how concentrated it was, then I know how many moles it took to neutralize.
If I know how much of this I started with, I can now find the molarity 12 12 12 12 12 12 12 12

13. Other Bases
Oxides (O2-) will also make water, but you'll need to use twice as much acid to neutralize:
O2- + 2H+ → H2O
Hydrides (H-) will make H2 when it reacts with acid or water...serious risk of explosion.
Amides (NH2-) will make ammonia (NH3) when it reacts with acid. Ammonia is a smelly gas. There's also some complications because ammonia itself is a weak base. We will not use amides. 13 13 13 13 13 13 13 13

14. Summary If not in perfect ratio, you will not get a neutral solution
Use chart and new molarity to get new pH
Remember to adjust for new volume
A titration is the process of measuring how much acid or base there is by adding a known concentration until it is neutral.
Most titrations use an indicator—something that changes color when you reach equal moles (neutral for strong acids/bases) 14 14 14 14 14 14 14 14