1. Acids Sour taste Change the color of acid-base indicators
(ex. turn litmus to red)
Some react with metals and release hydrogen gas
React with bases to produce salts and water
(salt = cation from a base and anion from an acid)
Contain H+ when dissolved in aqueous solutions
pH less than 7
Binary acids, oxyacids and organic acids

2. Bases Taste bitter Change the color of acid-base indicators
(ex. turn litmus to blue)
Dilute solutions feel slippery
React with acids to produce salts and water
pH more than 7
Many soluble bases (alkali) contain hydroxide ions (OH-)

3. Definitions of Acids and Bases
1. Arrhenius
Acid : compound that creates H+ in a solution
Base : compound that creates OH- in a solution
The H+ ion attracts other molecules so strongly that it normally exists as the hydronium ion (H3O+) when in water

4. Definitions of Acids and Bases (con’t)
2. Brønsted-Lowry
Most commonly used definition for acids and bases
Created by two scientists around the same time (1923)
A Brønsted-Lowry acid is a molecule or ion that is a proton donor (hydrogen ion, H+).
Ex. Hydrogen chloride acts as a Brønsted-Lowry acid when it reacts with ammonia.
HCl + NH3 → NH Cl-
Water can act as a Brønsted-Lowry acid
NH3(aq) + H2O(l) → NH OH-

5. A Brønsted-Lowry base is a molecule or ion that is a proton acceptor (gains a H+).
Ammonia accepts a proton from hydrochloric acid.
NH3 + HCl → NH Cl-
base acid
In a Brønsted-Lowry acid-base reaction, protons are transferred from one reactant to another (the acid to the base).

6. Conjugate acids and bases
The substance that remains after a Brønsted-Lowry acid has given up a proton is the conjugate base.
The substance that is formed when a base accepts a proton is the conjugate acid.
HF(aq) H2O(l) → F-(aq) H3O+(aq)
acid base conjugate conjugate
base acid

7. Monoprotic acids
Only have one acidic proton (one hydrogen ion)
ex. HClO4, HCl, HNO3
Polyprotic acids (diprotic, triprotic)
Can donate more than one proton per molecule
ex. H2SO4, H3PO4

8. Water can act as an acid or a base!!!
Interesting fact…
Water can act as an acid or a base!!!
Amphoteric compound: Any compound that can react as either an acid or a base

9. Measuring acidity or basicity
pH is a measure of how acidic or basic a solution is.
(“p” stands for potential and “H” stands for hydrogen; therefore, the potential of a substance to attract hydrogen ions)
pH ranges from 0 to 14.
Acidic solutions have pH values < 7
A pH of 7 is neutral.
Basic solutions have pH values >7

10. pH scale

11. pH Concentration of pure water at 25°C: [H+] = 1.0 ×10−7 M
[OH−] = 1.0 × 10−7 M
Brackets, [ ], symbolize the molarity concentration

12. pH + pOH = 14.0 pH = −log [H+] Calculating pH
The pH of a solution is the negative logarithm of the hydrogen ion concentration, [H+].
pH = −log [H+]
example: for a neutral solution [H+] = 1×10−7
pH = −log [H+] = −log(1 × 10−7) = −(−7.0) = 7.0
The pOH of a solution is defined as the negative logarithm of the hydroxide ion concentration, [OH−].
pOH = −log [OH–]
pH + pOH = 14.0

13. Practice problems
1. What is the pH of coffee if the [H+] is 1 x 10−5 M?
STEP 1 Enter the [H+] value:
Enter 1 x 105 (press 1 EE 5, then change sign )
STEP 2 Press log key and change the sign:
log (1 x 10−5) = [5]
STEP 3 Make the number of digits after the decimal point equal
to the number of significant figures in the coefficient:
[H+]= 1 x 10−5
Answer: pH is 5.0

14. Stomach acid (HCl) has a concentration of approximately 2 x 10−4 M
Stomach acid (HCl) has a concentration of approximately 2 x 10−4 M. What is the pH of the solution?
STEP 1 Enter the [H+] value: 2 x 104
(press 2 EE 4, then change sign)
STEP 2 Press log key and change the sign:
log (2 x 10−4) = [3.7]
STEP 3 Make the number of digits after the decimal
point equal to the number of significant figures in the coefficient [H+] = 2 x 10−4
Answer: pH is = 3.7

15. Calculating [H+] from pH
What is the concentration of nitric acid (HNO3) that has a pH of 3.80?
STEP 1 Enter the pH value, change sign: –3.80
STEP 2 Convert pH to concentration:
Use 2nd function key and then10x key
or inverse key and then log key
answer = −06
STEP 3 Adjust the significant figures in the coefficient (2 digit following decimal point = 2 digit in the coefficient):
Answer: [HNO3] = x 10−6 M