• Why do Acids and bases change ACIDS BASES
Sour taste (vinegar) Bitter taste (baking soda)
React with some metal to form H2 gas (Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
Feels slippery (soap)
Turns blue litmus red Turns red litmus blue
Arrhenius Definition
• Acid: produces H+ (or H3O+) when dissolved in water
HCl(aq) H+(aq) + Cl-(aq)H+(aq) + H2O(l) H3O+(aq)
NOTE: H3O+ = hydronium ion
• Base: produces OH- when dissolved in water.
NaOH(s) Na+(aq) + OH-(aq)
Bronsted-Lowry Definition Acids: proton (H+) donors
HF(aq) H+(aq) + F-(aq)H+(aq) + H2O(l) H3O+(aq)
Bases: proton acceptorsNH3(aq) + H2O(l) NH4
+(aq) + OH-(aq)
H2O: acts as an acid and a base = AMPHOTERIC
H
NH
H
H+ N+
H
H H
H
Strength of AcidsStrong Acids: ionize (splits up into ions) almost 100% in
water mostly ions in solution amount of HCl present is negligeable
HCl(aq) H+(aq) + Cl-(aq)
Weak acids: ionize poorly in water not many of these ions present in solution mostly acetic acid (HC2H3O2)
HC2H3O2(aq) C2H3O2-(aq) + H+(aq)
NOTE: strong acids are strong electrolytes and will conductelectricity better than weak acids.
Strength of BasesStrong Bases: ionize almost 100% in water
NaOH(s) Na+(aq) + OH-(aq)
Weak Bases: ionize poorly in water
NH3(l) + H2O(l) NH4+(aq) + OH-(aq)
NOTE: strong bases are strong electrolytes
Conjugate Acids and Conjugate Bases
• these differ by only one proton• Examples
HCl Cl-
SO42- HSO4
-
Lose a proton
Gain a proton
Acid Conjugate base of HCl
Base Conjugate acid of SO4
2-
Reactions with Water
Conjugate acid-base pair: CH3CO2H/CH3CO2-
Conjugate acid-base pair: H2O/H3O+
H C
H
H
C
O
O H
+ O
H H
H C
H
H
C
O
O - O
+ H H
H
acetic acid water acetate ion hydronium ion
Monoprotic, Diprotic and TriproticMonoprotic
· donates one acidic proton· eg: HCl + H2O H3O+ + Cl-
· only one H+ to donate
Diprotic
· donates two acidic protons· eg: H2SO4 + H2O H3O+ + HSO4
-
· HSO4- + H2O H3O+ + SO4
2-
Triprotic
· donates three acidic protons· eg: H3PO4 + H2O H3O+ + H2PO4
-
· three H+ to donate
a measure of acid strengthBy definition all acids contain at least one acidic proton
= H+
HA is a symbol used to represent any general acid HA H+(aq) + A-(aq)
H+ + H2O H3O+
[H+] = [H3O+]
If a lot of H3O+ is produced the solution is very acidic.
pH is directly related to [H3O+].
pH
H2O(l) + H2O(l) H3O+(aq) + OH-(aq)
This reaction does not occur to any great extent.[H3O+] = 1 x 10-7 mol/L[OH-] = 1 x 10-7 mol/LBecause both concentrations are equal water is said to be neutral.Therefore, if [H3O+] = [OH-] neutral [H3O+] > [OH-] acidic
[H3O+] < [OH-] basic
NOTE: [H3O+][OH-] = 1.0 x 10-14
Self-Ionization of Water
• Expressing hydronium concentrations in scientific notation isn’t very convenient. The pH scale was developed to make the expression of H3O+ concentration more convenient.
• [H3O+] is the concentration in mol/L
pH = -log[H3O+]
The concentration of H3O+ is 1.0 x 10-7. Calculate the pH.
Example 1: pH of Water
pH = -log[H3O+]
= -log(1.0 x 10-7)
= -(-7)
= 7
The pH of water is 7. Therefore pH 7 is neutral.
Determine the pH of a 1M solution of HCl.
Example 2
HCl (aq) H+ + Cl-
1M x
Therefore [H3O+] = 1
Therefore, pH = -log[H3O+]
= -log(1)
= 0
Therefore a 1M solution of HCl has pH 0.
What is the pH of a 0.01M solution of HCl?
Example 3
HCl (aq) H+ + Cl-
[H3O+] = 0.01 M
Therefore, pH = -log[H3O+]
= -log(0.01)
= 2
What is the pH of a 1M NaOH solution?
Example 4
pOH = -log[OH-] = -log(1) = 0
pH + pOH = 14
pH = 14 – pOH
pH = 14
Therefore a 1M solution of NaOH has pH 14. The pH
of a very basic solution.
Determine the pH of a 0.01M NaOH solution.
Example 5
pOH = -log[OH-] = -log(0.01) = 2
pH + pOH = 14 pH = 14 – pOH pH = 12
Therefore a 1M solution of NaOH has pH 12. The pH
of a basic solution.
The pH reading of a solution is 10.33. What is its hydrogen ion concentration?
Example 6
10-pH = [H+]
10-10.33 = [H+]
4.7 10-11 mol/L = [H+]
Base ten logarithm represents
an exponent log10(100) =2
102
Calculate the pH of a 0.00242 M H2SO4 solution .
Example 7
H2SO4 2H+ + SO42-
0.00242 M 0.00484M
pH = - log[H+]
= -log(0.00484)
= -(-2.315)
= 2.32
Acid-Base Indicators
• Can determine if the solution is acidic, basic or natural using various indicators
• Litmus paper, bromothyomol blue, phenolphthalein are some examples.
• Depending on the indicator they change colour at varying pH levels.
• Need to use various indicators to solve the pH level