Unit 4 – Solutions and Solubility
Chapter 10 – Acids and Bases
10.1 – Arrhenius Acids and Bases
Properties of Acids and Bases
ACIDS
BASES
Sour taste (vinegar)
Bitter taste (baking soda)
React with some metal to form H2 gas Feels slippery (soap)
(Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Turns blue litmus red
Turns red litmus blue
Arrhenius Definition
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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
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Base: produces OH- when dissolved in water.
NaOH(s) → Na+(aq) + OH-(aq)
Bronsted-Lowry Definition
Acids: proton (H+) donor
Bases: proton acceptor
H2O: acts as an acid and a base = AMPHOTERIC
Strength of Acids
Strong 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 conduct
electricity better than weak acids.
Strength of Bases
Strong 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
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these differ by only one proton
Examples
Lose a proton
HCl
Cl-
SO4
2-
Gain a proton
HSO4-
Reactions with Water
Conjugate acid-base pair:
Conjugate acid-base pair:
Monoprotic, Diprotic and Triprotic
Monoprotic
∙
donates only one proton
∙
eg: HCl(aq)
∙
only one H+ to donate
Diprotic
∙
donates 2 protons
∙
eg: H2SO4(aq)
Triprotic
∙
donates three protons
∙
eg: H3PO4(aq)
∙
three H+ to donate
pH
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a measure of acid concentration
By 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 + + H 2O → H 3O +
If a lot of H3O+ is produced the solution is very
acidic.
pH is directly related to [H3O+].
Self-Ionization of Water
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/L
Because both concentrations are equal water is
said to be neutral.
NOTE: [H3O+][OH-] = 1.0 x 10-14
+
pH = -log[H3O ]
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Expressing hydronium concentrations in
scientific notation isn’t very convenient. The pH
scale was developed to make the expression of
H3O+ concentration more convenient.
Example 1: pH of Water
In pure water, the concentration of H3O+ is 1.0 x 10-7.
Calculate the pH.
Example 2
Determine the pH of a 1M solution of HCl.
Example 3
What is the pH of a 0.01M solution of H2SO4?
What is the pH of a 0.001M solution of H3PO4
Example 4
pH + pOH = 14
What is the pH of a 1M NaOH solution?
Example 5
Determine the pH of a 0.01M NaOH solution.
pH Scale
pH < 7
pH = 7
pH > 7
acidic
neutral
basic
Example 6
The pH reading of a solution is 10.33. What is its hydrogen ion
concentration.
Example 7
Calculate the pH of a 0.00242 M H2SO4 solution .
HOMEWORK
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Read 10.1, p.464-474
Complete worksheet “Acids, Alkali, and pH”