Importance:
The chapter "Acids, bases and salts" carries significant weightage around \(3\) marks, highlighting its significance in the overall curriculum. A clear understanding of this chapter will enhance how acids, bases, and salts interact with each other and their impact on various natural and industrial processes.
Question distribution:
- Section A or B (\(1\) or \(2\) marks) - One question
- Section C (\(3\) mark) - One question
(Note: The exact mark distribution may vary slightly across examinations)
Learning objectives:
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Identify acids and bases using natural indicators (such as litmus) and synthetic indicators (such as phenolphthalein and methyl orange).
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Describe and explain the chemical properties of acids and bases, including their reactions with metals, carbonates, and oxides.
- Explore how acids and bases neutralise each other.
- Prove that acids and bases conduct electricity, identifying this as a common property due to the presence of ions in their aqueous solutions.
- Compare and contrast the properties of acids and bases based on their taste, pH, and reaction behaviour.
Acids and bases:
| Property | Acids | Bases |
| Taste | Sour | Bitter |
| Nature | Corrosive | Slippery or soapy |
| Ions released in aqueous solution | \(H^+\) ions | \(OH^-\) ions |
| Litmus test | Turn blue litmus red | Turn red litmus blue |
| Phenolphthalein | Colourless | Pink |
| Methyl orange | Red | Yellow |
| Onion, vanilla essence, clove oil | Retains the odour | Odourless |
| pH range | Less than \(7\) | Greater than \(7\) |
| Electrical conductivity | Conducts electricity due to presence of ions (\(H^+\)) | Conducts electricity due to ions (\(OH^-\)) |
- Strong acids: Completely ionise in water and release more \(H^+\) ions - \(H_2SO_4\), \(HCl\), \(HNO_3\) and most of inorganic acids.
- Weak acids: Partially ionise in water and release fewer \(H^+\) ions - \(CH_3COOH\), \(H_2CO_3\), most of organic acids.
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Strong bases: Completely ionise in water and release more \(OH^-\) ions - \(NaOH\), \(KOH\).
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Weak bases: Partially ionise in water and release fewer \(OH^-\) ions - \(NH_4OH\).
Reactions of acids and bases:
| Reaction | Acids | Bases | Example | Test |
| Metals | Form salt + hydrogen gas | Form salt + hydrogen gas |
Acid: \(Zn + 2HCl → ZnCl_2 + H_2↑\)
Base: \(2NaOH + Zn → Na_2ZnO_2 + H_2↑\)
|
Pop sound |
| Metal carbonates and bicarbonates | Produce salt + water + \(CO_2\) gas | No reaction |
\(Na_2CO_3 + 2HCl → 2NaCl + H_2O + CO_2\)
|
Limewater turns milky
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| Neutralisation | Reacts with base to form salt + water | Reacts with acid to form salt + water |
\(HCl + NaOH → NaCl + H_2O\)
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Exothermic
|
| Metal/non - metal oxide | React with metal oxides to form salt + water | React with non-metal oxides to form salt + water |
Acid: \(MgO + 2HCl → MgCl_2 + H_2O\)
Base: \(2NaOH + CO_2 → Na_2CO_3 + H_2O\)
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Metallic oxides are basic.
Non-metallic oxides are acidic.
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Acids and bases exhibit unique chemical properties through their reactions with metals, oxides, and carbonates, helping us understand their real-world significance. In the next session, we will explore the pH scale, its importance, and the key chemicals obtained from common salt.