Acids, Bases, and Salts
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ACIDS, BASES, AND SALTS
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PRIOR LEARNING QUIZ
1. Water is made of hydrogen and oxygen atoms.
2. Acids always taste sweet.
3. A pH of 7 is neutral.
4. Alkalis are slippery to the touch.
5. Alkalis have a pH below 7.
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PRIOR LEARNING QUIZ ANSWERS
1. True
2. False
3. True
4. True
5. False
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OBJECTIVES
Define acids and bases.
Define strong acids and weak acids.
Compare hydrogen ion concentration, neutrality, relative acidity and alkalinity in terms of colour and pH using universal indicator paper.
Describe the neutralisation reaction between an acid and an alkali to produce water.
Describe acidic, basic, and amphoteric oxides.
Describe characteristic properties of acids in reactions with:
(a) metals
(b) bases
(c) carbonates
Describe effects of acids and alkalis on indicators:
(a) litmus
(b) thymolphthalein
(c) methyl orange
Describe characteristic properties of bases in reactions with:
(a) acids
(b) ammonium salts
Describe preparation, separation and purification of soluble salts.
Describe general solubility rules for salts.
Describe preparation of insoluble salts.
Define a hydrated substance.
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THE PH SCALE
The pH scale ranges from 0 to 14.
Acids: pH < 7
Neutral: pH = 7
Alkalis: pH > 7
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ACIDS
Acids in aqueous solutions contain hydrogen ions (H⁺).
pH is lower than 7.
Taste sour and are corrosive.
Example: HCl (aq) - hydrochloric acid.
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STRONG ACIDS
Strong acids dissociate completely in water releasing all H⁺ ions, making solutions very acidic.
Example: HCl → H⁺ + Cl⁻
Other examples: sulfuric acid (H₂SO₄), nitric acid (HNO₃).
Higher conductivity due to more mobile ions.
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WEAK ACIDS
Weak acids only partially dissociate in water.
Example: vinegar (ethanoic acid, CH₃COOH) dissociates: CH₃COOH ⇌ H + CH₃COO.
Other example: carbonic acid (H₂CO₃).
Lower conductivity due to fewer mobile ions.
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THE PH SCALE OF STRONG AND WEAK ACIDS
Higher hydrogen ion concentration equals lower pH and stronger acid.
Scale: 0 (strong acid) to 14 (strong base).
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BASES
Bases are metallic oxides or hydroxides (e.g. NaOH, MgO).
Bases that dissolve in water are called alkalis.
Alkalis contain hydroxide ions (OH⁻) and have pH > 7.
Corrosive in nature.
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STRONG AND WEAK BASES
Strong Bases
Dissociate completely in water releasing all OH⁻ ions.
Example: NaOH → Na⁺ + OH⁻.
Weak Bases
Partially dissociate in water.
Example: ammonium hydroxide (NH₄OH) ⇌ NH₄ + OH.
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THE BRONSTED-LOWRY THEORY
Acids: Proton (H⁺) donors.
Bases: Proton (H⁺) acceptors.
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THE BRONSTED-LOWRY THEORY EXAMPLES
Example: HC (aq) + H₂O → H3O⁺ (aq) + C.
NH₃ + H₂O → NH₄⁺ + OH⁻.
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CONCENTRATION OF IONS IN WATER
[H⁺] > [OH⁻]: pH < 7 (Acidic)
[H⁺] = [OH⁻]: pH = 7 (Neutral)
[H⁺] < [OH⁻]: pH > 7 (Alkaline)
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UNIVERSAL INDICATOR
Full range indicator showing the pH scale from 0 to 14.
Changes colour based on acidity or alkalinity.
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LITMUS PAPER
Acid: Blue litmus turns red.
Base: Red litmus turns blue.
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METHYL ORANGE
Acid: Colour is red.
Alkali: Colour is yellow.
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THYMOLPHTHALEIN
Acid: Colourless.
Neutral: Colourless.
Base: Blue.
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TRY THIS!
PHET Simulation: Acid-Base Solution.
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OXIDES
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BASIC OXIDES
Generally metallic oxides (e.g. CaO, CuO).
React with acids, forming alkaline solutions in water.
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ACIDIC OXIDES
Generally non-metallic oxides (e.g. SO₂, NO₂).
React with bases, forming acidic solutions in water.
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AMPHOTERIC OXIDES
React with both acids and bases.
Examples: ZnO, Al₂O₃.
Reactions: e.g., ZnO + 2HCl → ZnCl₂ + H₂O
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NEUTRAL OXIDES
Do not react with acids or bases.
Examples: CO, NO.
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CHEMICAL REACTIONS OF ACIDS
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ACID + BASE (NEUTRALIZATION)
Reaction: ACID + BASE → SALT + WATER
Example: HCl + NaOH → NaCl + H₂O.
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ACID + AMMONIA
Reaction: ACID + AMMONIA → AMMONIUM SALT
Example: HCl + NH₃ → NH₄Cl.
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ACIDS AND METAL CARBONATES
Observations: Effervescence/bubbles formed.
Reaction: Acid + (metal) carbonate → Salt + Water + Carbon Dioxide.
Example: HCl + CaCO₃ → CaCl₂ + H₂O + CO₂.
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ACIDS AND METALS
Observations: Effervescence/bubbles formed.
Reaction: Acid + Metal → Salt + Hydrogen.
Example: HCl + Zn → ZnCl₂ + H₂.
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METALS REACTIVITY
Not all metals react with acids, e.g. copper (Cu), silver (Ag), gold (Au), platinum (Pt).
Reactivity series dictates that metals must be more reactive than hydrogen to displace it in acids.
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IDENTIFYING STRONG AND WEAK ACIDS
Higher conductivity indicates strong acids.
More effervescence when adding a carbonate indicates stronger acids.
More effervescence from metal reaction indicates stronger acids.
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CHEMICAL REACTIONS OF BASES
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NEUTRALIZATION OF ACID + BASE
Reaction: ACID + BASE → SALT + WATER.
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BASE + AMMONIUM SALT
Reaction: BASE + AMMONIUM SALT → SALT + AMMONIA + WATER.
Example: Ca(OH)₂ + NH₄Cl → CaCl₂ + NH₃ + H₂O.
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WRITING IONIC EQUATIONS
Write the full balanced equation.
Write ions separately from ionic compounds.
Cancel out ions that appear on both sides.
Write the net ionic equation.