ACIDS & BASES
Important Aqueous Solutions
NC Essential Standards
• 3.2.1 Classify substances using the hydronium and
hydroxide concentrations
• Distinguish between acids and bases based on formula and
chemical properties
• Differentiate between concentration (molarity) and strength (degree
of dissociation)
• Use pH to identify acids and bases.
• Interpret pH scale in terms of the exponential nature of pH values in
terms of concentrations.
• Relate the color of indicator to pH using ranges provided in a table.
• Compute pH, pOH, [H⁺] and [OH⁻]
• 3.2.2 Distinguish properties of acids and bases related to taste, touch,
reaction with metals, electrical conductivity, and identification with
indicators such as litmus paper and phenolphthalein.
Overview of Key Concepts
• http://ed.ted.com/on/j4JlNr0Y#watch
• Introduction 5 minutes
Distinguish properties of acids and bases related to taste, touch,
reaction with metals, electrical conductivity, and identification with
indicators such as litmus paper and phenolphthalein.
• Properties of acids and bases
• http://ed.ted.com/lessons/the-strengths-and-weaknesses-
of-acids-and-bases-george-zaidan-and-charles-morton
Notes: Make 4 columns to easily jot down notes from the video
• Acid properties
Base properties Examples: Strong Weak
Note: Think H+ ions when protons are used.
Review: Names and Formulas
• Common acids that you must know
• All are dissolved in water (aqueous solutions)
• HCl
• HBr
• HF
• HNO₃
• H₂SO₄
• HC₂H₃O₂
• H₂CO₃
• H₃PO₄
Review: Names and Formulas
• Common bases that you must know:
• NaOH
• Mg(OH)₂
• NH₃
Acid & Base demonstrations
• http://www.youtube.com/watch?v=ti_E2ZKZpC4
• Introduction - properties (5 minutes)
• http://ed.ted.com/on/j4JlNr0Y
Arrenhius Definition of Acids and Bases
• Acids release H⁺ ion
• Also known as hydronium ions (H₃O⁺)
• Bases release OH⁻¹ (hydroxide) ions
• Other definitions:
• Bronsted Lowery
• Lewis
pH scale
pH scale
• pH values
• pH = - log [H⁺]
pH Scale
Strong
Acids
Neutral
⇓
Weak & Dilute
Acids
Weak & Dilute
Bases
Strong
Bases
Chemistry Reference Tables
What do these formulas mean?
Ions in Solutions
Neutral
[H⁺]
[OH⁻]
In water: [H⁺]= [ OH⁻]
pH = 7 pOH = 7
pOH Scale
Weak
Base
Weak & Dilute
Bases
Neutral
⇓
Weak & Dilute
Acids
Chemistry
Reference Tables
pH + pOH = 14
Strong
Acids
Answers
Examples
of Acids
and
Bases
pH Scale
• http://www.johnkyrk.com/pH.html
pH indicators
• What is the approximate pH of the solution tested in
the picture? Is the solution an acid or a base? Is it
strong or weak?
pH Indicators
• Litmus Paper
• Phenolphthalein
Blue - indicates base
Red - indicates acid
pH below
8
pH 8 - 12
pH above
12
Colorless
Fuchsia
Colorless
Litmus (pH indicator)
below pH
4.5
4.5
above pH
8.3
↔
8.3
pH Indicators -
different indicators for different purposes
Scientist choose indicators based on the solution and process to
be monitored.
Universal Indicator
Bromothymol Blue
Acid = yellow
Neutral = green
Base = blue
pH range
Description
Colour
<3
Strong acid
Red
3-6
Acid
Orange/Yellow
7
Neutral
Green
8-11
Alkali
Blue
> 11
Strong alkali
Violet/Purple
Strength of Acids and Bases
• http://ed.ted.com/lessons/the-strengths-and-weaknesses-
of-acids-and-bases-george-zaidan-and-charles-morton
• 4 minutes
• Write notes:
Concentration⇎ Strength
• Concentrated or dilute - Molarity
• 6M vs. 0.6 M
Strength or weak = degree to which acids or bases
separate into ions
Strength vs. Concentration
• Strength in acids
• Based on degree H⁺ ions separate from the anion
• Proportion of acid molecules in which H⁺ separate compared
to how many acid molecules do not separate
• Strong acids = most H⁺ separate
• Examples:
HCl, HNO₃ and H₂SO₄
• Weak acids = only some H⁺ separate
• Examples:
HF, HC₂H₃O₂
• Strength of Bases
• Strong = most OH⁻ separate from the metal
Reacting acids and bases
• HCl (aq) + Na(OH) (aq) → HOH + NaCl
• Write the word formula
• Identify the type of chemical reaction
• What is happening with the reactants and products?
• Ionic equation:
• Solubility rules:
Neutralization reactions
• Special double replacement reaction
• Always:
• Reactants: Acid + Base (any order)
• Products:
Salt (ionic compound) +
• Practice:
•
• sulfuric acid and calcium hydroxide
Water
Neutralization reactions
• Acid
+
Base → Salt + Water
• sulfuric acid and calcium hydroxide
• potassium hydroxide and nitric acid
• carbonic acid and magnesium hydroxide
• hydrobromic acid and lithium hydroxide
Salts formed in the previous problems
sulfuric acid and calcium hydroxide
salt name:
calcium sulfate
salt formula: CaSO4
potassium hydroxide and nitric acid
salt name:
potassium nitrate
salt formula: KNO3
carbonic acid and magnesium hydroxide
salt name:
magnesium carbonate salt formula: MgCO3
hydrobromic acid and lithium hydroxide
salt name:
lithium bromide
salt formula: LiBr