Curriculum
Science Grade 10
Grade 10 Science
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Chapter 1. Chemical Reactions
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Chapter 2: Acids, Bases and Salts
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Chapter 3: Metals and Non-metals
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Chapter 4: Carbon and its Compounds
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Chapter 5: Life Processes
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Chapter 6: Control and Coordination
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Chapter 7: How do Organisms Reproduce?
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Chapter 8: Heredity
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Chapter 9: Light Reflection and Refraction
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Chapter 10: The Human Eye and the Colourful World
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Chapter 11: Electricity
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Chapter 12: Magnetic Effects of Electric Current
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Chapter 13: Our Environment
Interactive Worksheets
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Chapter 2: Acids, Bases and Salts
Acids, Bases
and Salts
From the tang of lemon to the sting of bee venom — explore the chemistry of acids, bases, salts, the pH scale, neutralisation, and essential everyday chemical products.
| 🧪 Acids & Bases | 📊 pH Scale | ⚗ Neutralisation | 🏭 Salts & Industry |
| 📋 Chapter at a Glance |
| Section | Topics Covered | Key Terms |
| 2.1 Chemical Properties | Acids/bases in lab, reactions with metals, metal carbonates, hydrogencarbonates, neutralisation, metallic & non-metallic oxides | Indicator, Olfactory indicator, Neutralisation, Salt, Basic oxide, Acidic oxide |
| 2.2 Common Properties | H⁺ ions in acids, OH⁻ ions in bases, ionisation in water, dilution, exothermic dissolution, strong vs weak acids/bases | H⁺(aq), Hydronium ion H₃O⁺, OH⁻(aq), Alkali, Dilution, Ionisation |
| 2.3 pH Scale | Universal indicator, pH 0–14, importance of pH in everyday life, acid rain, tooth decay, digestive system | pH, Universal indicator, Acid rain, Antacid, Strong acid, Weak acid |
| 2.4 More About Salts | Family of salts, pH of salts, chlor-alkali process, bleaching powder, baking soda, washing soda, water of crystallisation, Plaster of Paris | Brine, Chlor-alkali, NaHCO₃, Na₂CO₃, Water of crystallisation, Gypsum, Plaster of Paris |
| 🔑 Key Definitions |
| 2.1 — Chemical Properties of Acids and Bases |
Acids and bases have been known since ancient times — acids for their sour taste and bases for their bitter taste and soapy feel. However, we never taste chemicals directly in the laboratory. Instead, we use indicators to test them. Litmus (extracted from lichen, a plant in the Thallophyta division) is the most common natural indicator — it turns red in acid and blue in base.
| 📐 Diagram 1: Indicator Colour Chart |
| Indicator | In Acid | In Base | In Neutral |
| Blue Litmus | Turns RED | Stays BLUE | Stays Blue |
| Red Litmus | Stays RED | Turns BLUE | Stays Red |
| Phenolphthalein | Colourless | PINK/Red | Colourless |
| Methyl Orange | RED/Pink | YELLOW | Orange |
| Turmeric | Yellow | Reddish-brown | Yellow |
| 2.1.2 — How do Acids and Bases React with Metals? |
When acids react with metals, they displace hydrogen gas and form a salt. When bases (like NaOH) react with certain metals (like zinc, aluminium), they also produce hydrogen gas along with a salt. The hydrogen burns with a ‘pop’ sound — the test for H₂ gas.
| 📐 Diagram 2: Zinc + Dilute Sulphuric Acid (Activity 2.3) |
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| 2.1.3 — Metal Carbonates and Hydrogencarbonates with Acids |
All metal carbonates and hydrogencarbonates react with acids to produce a salt, carbon dioxide gas and water. The CO₂ gas produced turns lime water milky — this is the standard test for CO₂.
| 📐 Diagram 3: CO₂ passed through Lime Water (Activity 2.5) |
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| 2.1.4 — Neutralisation (Acid + Base) |
When an acid and a base react together, they neutralise each other’s effect to form a salt and water. This is called a neutralisation reaction. Phenolphthalein (pink in base, colourless in acid) is used to detect the endpoint.
| General Reaction: Acid + Base → Salt + Water HX + MOH → MX + H₂O At ionic level: H⁺(aq) + OH⁻(aq) → H₂O(l) Example: |
Metal Oxide + Acid (similar to neutralisation): Metal oxide + Acid → Salt + Water CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l) (Black CuO dissolves → Blue-green CuCl₂) Metallic oxides are basic oxides. |
| 2.2 — What do All Acids and All Bases Have in Common? |
Although glucose and alcohol also contain hydrogen, they are not acids. The key is whether hydrogen ions (H⁺) are produced in water. Acids dissolve in water to produce H⁺(aq) ions — these carry electric current, making the bulb glow in Activity 2.8. Glucose and alcohol don’t produce ions, so the bulb does NOT glow with them.
| Substance | Contains H? | Produces H⁺ in water? | Bulb glows? | Acidic? |
| HCl, H₂SO₄, HNO₃ | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes |
| Glucose, Alcohol | ✓ Yes | ✗ No | ✗ No | ✗ No |
| 2.2.1 — Acids and Bases in Water: Ionisation |
Dry HCl gas does NOT change the colour of dry litmus paper — proving that H⁺ ions are only produced in the presence of water. H⁺ ions cannot exist alone; they combine with water to form the hydronium ion (H₃O⁺).
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| 2.3 — How Strong are Acid or Base Solutions? The pH Scale |
The pH scale (0–14) measures hydrogen ion concentration in a solution. It uses a universal indicator — a mixture of several indicators that shows a different colour for each pH value. The ‘p’ in pH stands for potenz (German: power). Higher H⁺ concentration means lower pH.
| 📐 Diagram 4: The pH Scale (0 to 14) |
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| 2.3.1 — Importance of pH in Everyday Life |
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🫀 Human Body
Our body works within pH 7.0–7.8. Slightly alkaline blood (pH ~7.4) is essential. Living organisms can survive only in a narrow pH range. Even a slight change in blood pH can be fatal. |
🦷 Tooth Decay
Tooth decay starts when mouth pH drops below 5.5. Bacteria produce acids from sugar, corroding tooth enamel (calcium hydroxyapatite). Using basic toothpaste neutralises the acid and prevents decay. Clean teeth after meals! |
🌧 Acid Rain
When pH of rain water falls below 5.6, it is called acid rain. It is caused by dissolved SO₂ and NO₂ from burning of fossil fuels. Acid rain lowers river pH, making aquatic life survival difficult, and damages buildings and soil. |
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🌱 Soil pH
Plants need a specific pH range for healthy growth. If soil is too acidic, farmers add calcium oxide (quick lime), slaked lime (calcium hydroxide) or chalk (CaCO₃) to neutralise acidity and increase soil pH. |
🍽 Stomach Acid
The stomach produces HCl (pH ~1.2) to digest food. During indigestion, excess acid causes pain. Antacids (mild bases like Mg(OH)₂ — Milk of magnesia) are used to neutralise excess acid and provide relief. |
🐝 Animal/Plant Defence
Bee sting injects formic (methanoic) acid — baking soda (base) provides relief. Nettle leaf hairs inject methanoic acid — dock leaf (basic) soothes the pain. Venus atmosphere has H₂SO₄ clouds — hostile to life! |
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| 2.4 — More About Salts |
| 2.4.2 — pH of Salts |
| Salt formed from | Nature of salt | pH | Example |
| Strong acid + Strong base | Neutral | = 7 | NaCl (HCl + NaOH) |
| Strong acid + Weak base | Acidic | < 7 | NH₄Cl (HCl + NH₄OH) |
| Weak acid + Strong base | Basic | > 7 | Na₂CO₃ (H₂CO₃ + NaOH) |
| 2.4.3 — Chemicals from Common Salt (NaCl) |
Common salt (sodium chloride, NaCl) — obtained from sea water or rock salt (mined underground) — is a vital raw material for producing many essential chemicals used in industry and daily life.
| 📐 Diagram 5: The Chlor-alkali Process |
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🧴 Sodium Hydroxide (NaOH)
From chlor-alkali process. Formed near cathode. Uses: soaps, detergents, paper making, de-greasing metals, artificial fibres. |
🌊 Bleaching Powder Ca(ClO)₂
Cl₂ on dry slaked lime: 2Ca(OH)₂ + 2Cl₂ → Ca(ClO)₂ + CaCl₂ + 2H₂O. Uses: bleaching textiles/wood pulp/laundry; oxidising agent; disinfecting drinking water. |
🥖 Baking Soda NaHCO₃
NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃. Uses: baking powder (CO₂ makes bread spongy); antacid; soda-acid fire extinguisher. Mild non-corrosive basic salt. |
🫧 Washing Soda Na₂CO₃·10H₂O
Heat NaHCO₃ → Na₂CO₃; recrystallise with water → Na₂CO₃·10H₂O. Uses: glass, soap, paper industries; manufacture of borax; cleaning agent; removes permanent water hardness. |
| 2.4.4 — Water of Crystallisation & Plaster of Paris |
| 📐 Diagram 6: Copper Sulphate + Water of Crystallisation (Activity 2.15) |
Water of crystallisation = fixed number of H₂O molecules per formula unit. CuSO₄·5H₂O has 5; Na₂CO₃·10H₂O has 10; CaSO₄·2H₂O (gypsum) has 2. |
| 📐 Diagram 7: Gypsum → Plaster of Paris → Gypsum |
Plaster of Paris must be stored in moisture-proof containers — contact with even a little moisture causes it to set into hard gypsum, making it useless. |
| 🌿 Naturally Occurring Acids (Table 2.3) |
| Natural Source | Acid | Natural Source | Acid |
| Vinegar | Acetic acid (ethanoic acid) | Sour milk / Curd | Lactic acid |
| Orange | Citric acid | Lemon | Citric acid |
| Tamarind | Tartaric acid | Ant sting | Methanoic acid (formic acid) |
| Tomato | Oxalic acid | Nettle sting | Methanoic acid (formic acid) |
| 🔬 Activities (2.1 to 2.15) — Lab Experiments |
▶ Activity 2.1 — Testing with Indicators
Procedure: Put a drop of each solution on a watch-glass. Test with each indicator.
Observations: Acids turn blue litmus red, phenolphthalein stays colourless, methyl orange turns red/pink. Bases turn red litmus blue, phenolphthalein turns pink, methyl orange turns yellow.
Conclusion: Indicators change colour depending on whether the substance is acidic or basic.
▶ Activity 2.2 — Olfactory Indicators (Onion, Vanilla, Clove)
Procedure: Add HCl and NaOH to onion strips, vanilla and clove oil separately. Note odour changes.
Observations: Onion — loses smell in NaOH (base), retains in HCl. Vanilla — loses smell in base. Clove oil — loses smell in acid (NaOH doesn’t affect it).
Conclusion: Onion and vanilla are olfactory indicators (respond to bases). Clove responds to acids. These can be used to detect acids/bases where colour indicators are not visible.
▶ Activity 2.3 — Acid + Metal → Hydrogen Gas
Procedure: Add dilute H₂SO₄ to Zn granules. Pass evolved gas through soap solution. Bring a burning candle near H₂-filled bubble.
Observations: Bubbles on Zn surface. Soap bubbles filled with gas rise. The bubble burns with a ‘pop’ sound.
Conclusion: H₂ gas is evolved. Equation: Zn + H₂SO₄ → ZnSO₄ + H₂↑ [Displacement reaction]. All common acids (HCl, HNO₃, CH₃COOH) give similar results.
▶ Activity 2.4 — Base + Metal → Hydrogen Gas
Procedure: Add NaOH solution to zinc metal, warm gently. Test evolved gas by burning.
Observations: H₂ gas is evolved (pops near flame), just like with acids.
Conclusion: Bases can also react with certain metals (Zn, Al) to evolve H₂. Equation: 2NaOH(aq) + Zn(s) → Na₂ZnO₂(s) + H₂(g) [sodium zincate formed]. Not all metals react this way.
▶ Activity 2.5 — Acid + Carbonate/Bicarbonate → CO₂
Procedure: Add HCl to each test tube. Pass evolved gas through lime water.
Observations: Brisk effervescence (CO₂) in both tubes. Lime water turns milky white (CaCO₃ precipitate). On passing excess CO₂, milkiness disappears (Ca(HCO₃)₂ forms — soluble).
Equations: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂; NaHCO₃ + HCl → NaCl + H₂O + CO₂; Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O
▶ Activity 2.6 — Neutralisation (Acid + Base)
Procedure: Add phenolphthalein to NaOH (turns pink). Add HCl drop by drop. Observe colour change. Then add NaOH back.
Observations: NaOH + phenolphthalein = pink. Adding HCl makes it colourless (acid neutralises base). Adding NaOH again restores pink colour.
Conclusion: Acid and base neutralise each other. NaOH + HCl → NaCl + H₂O. At endpoint (neutral), phenolphthalein is colourless.
▶ Activity 2.7 — Metal Oxide + Acid
Procedure: Add dilute HCl slowly to CuO while stirring.
Observations: Black CuO dissolves. Solution turns blue-green (copper chloride CuCl₂ formed).
Conclusion: Metallic oxides are basic oxides — they react with acids to form salt + water, just like bases. CuO + 2HCl → CuCl₂ + H₂O. Non-metallic oxides (CO₂) react with bases and are acidic oxides.
▶ Activity 2.8 — Electrical Conductivity: Acids vs Glucose/Alcohol
Procedure: Pour each solution into beaker. Connect nails to battery through bulb. Observe whether bulb glows.
Observations: Bulb glows with HCl and H₂SO₄. Bulb does NOT glow with glucose and alcohol.
Conclusion: Acids produce ions (H⁺ and anions) in water which conduct electricity. Glucose/alcohol do not produce ions — hence not acidic despite containing hydrogen.
▶ Activity 2.9 — Dry HCl vs Wet HCl: Need for Water
Procedure: Add conc. H₂SO₄ to NaCl. Pass gas through dry litmus, then wet litmus.
Observations: Dry HCl gas does NOT change dry litmus. Moist/wet litmus paper turns red.
Conclusion: HCl gas is not acidic in the absence of water. H⁺ ions form ONLY in the presence of water: HCl + H₂O → H₃O⁺ + Cl⁻. Water is essential for ionisation and acidic behaviour.
▶ Activity 2.10 — Dilution of Acids/Bases: Exothermic Process
Procedure: Add a few drops of conc. H₂SO₄ to water (NOT the other way). Touch base of beaker. Repeat with NaOH pellets.
Observations: The beaker becomes very hot — dissolving is highly exothermic for both acid and base.
Safety conclusion: Always add ACID to WATER. If water is added to acid, heat generated can cause the mixture to splash, causing burns. Dilution decreases H₃O⁺/OH⁻ concentration per unit volume.
▶ Activity 2.11 — Measuring pH of Common Solutions
Procedure: Test pH of each solution using universal indicator paper.
Expected results: Gastric juice ~1.2, lemon ~2–3, cola ~3, coffee ~5, pure water ~7, sea water ~8, milk of magnesia ~10, NaOH ~14.
Conclusion: pH paper gives approximate pH values. Neutral = 7, acidic <7, basic >7.
▶ Activity 2.12 — Soil pH Test
Procedure: Add 5 mL water to 2g soil, shake, filter, test filtrate pH with universal indicator paper.
Conclusion: Different soils have different pH values. Plants need specific pH for healthy growth. Acidic soil can be treated with quick lime, slaked lime or chalk (all alkaline) to neutralise the acidity.
▶ Activity 2.13 — Family of Salts
Sulphate family: K₂SO₄, Na₂SO₄, CaSO₄, MgSO₄, CuSO₄ (share SO₄²⁻).
Sodium family: Na₂SO₄, NaCl, NaNO₃, Na₂CO₃ (share Na⁺).
Chloride family: NaCl, NH₄Cl (share Cl⁻).
Conclusion: Salts with the same positive or negative radical belong to the same family.
▶ Activity 2.14 — pH of Salt Solutions
Test: Dissolve NaCl, KNO₃, AlCl₃, ZnSO₄, CuSO₄, CH₃COONa, Na₂CO₃, NaHCO₃ in distilled water. Test with litmus and pH paper.
Results: NaCl, KNO₃ = neutral (pH 7). AlCl₃, ZnSO₄, CuSO₄ = acidic (pH <7, strong acid + weak base). Na₂CO₃, NaHCO₃, CH₃COONa = basic (pH >7, weak acid + strong base).
Conclusion: The pH of a salt solution depends on the relative strengths of the acid and base from which it was formed.
▶ Activity 2.15 — Water of Crystallisation (CuSO₄)
Procedure: Heat crystals. Observe colour change and water droplets in tube. Add 2–3 drops of water to cooled anhydrous CuSO₄.
Observations: Blue crystals turn white on heating. Water droplets condense on cool upper tube. Adding water to white powder restores blue colour.
Conclusion: CuSO₄·5H₂O contains 5 water molecules of crystallisation. Heating removes them (anhydrous CuSO₄ = white). Adding water hydrates it back. This confirms water of crystallisation.
| ✏ Worked Examples |
Write the balanced equation for dilute H₂SO₄ reacting with zinc granules. Identify the type of reaction.
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Balanced: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Check: Zn=1=1✓, H=2=2✓, S=1=1✓, O=4=4✓
Type: Displacement reaction (Zn displaces H from acid). Also produces H₂ gas — test: burns with pop sound.
Why does the colour of phenolphthalein change from pink to colourless when HCl is added to NaOH solution?
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Why do HCl and H₂SO₄ show acidic properties in water but dry HCl gas does not?
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Five solutions have pH values 4, 1, 11, 7, 9. Identify each. Arrange in increasing order of H⁺ concentration.
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Increasing H⁺ concentration means decreasing pH, so order: pH 11 → pH 9 → pH 7 → pH 4 → pH 1 (i.e., least H⁺ at pH 11, most H⁺ at pH 1).
Explain the chlor-alkali process. Why is it called ‘chlor-alkali’?
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It is called chlor-alkali because: “Chlor” refers to chlorine gas produced at the anode. “Alkali” refers to sodium hydroxide (an alkali) produced near the cathode. Three useful products: Cl₂ (water treatment, PVC), H₂ (fuel, fertilisers), NaOH (soaps, detergents, paper).
Metal compound A reacts with dilute HCl to produce effervescence. Gas extinguishes a burning candle. One product is CaCl₂. Write the balanced equation.
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Balanced equation: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
Ca=1=1✓, C=1=1✓, O=3=3✓, H=2=2✓, Cl=2=2✓
Why should curd and sour substances not be kept in brass or copper vessels?
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Fresh milk has pH 6. What happens to pH as it turns to curd? Why?
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A milkman adds a small amount of baking soda to fresh milk. (a) Why does he shift the pH to slightly alkaline? (b) Why does this milk take longer to set as curd?
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(b) For milk to set as curd (coagulate), the pH must fall sufficiently (bacteria need acidic environment to grow and produce enough lactic acid). Since baking soda keeps neutralising the acid produced, it takes longer for the pH to fall to the level needed for curd formation.
Why is Plaster of Paris stored in moisture-proof containers?
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CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O (sets hard)
If exposed to moisture in the air, it will absorb water and set into hard gypsum even before use — making it completely useless. Moisture-proof storage keeps it dry and ready to use.
Equal lengths of Mg ribbon in HCl (tube A) and CH₃COOH (tube B) — same concentration. Which tube fizzes more vigorously and why?
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Reactions: Mg + 2HCl → MgCl₂ + H₂↑ | Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂↑
10 mL NaOH is completely neutralised by 8 mL HCl. If 20 mL of same NaOH is taken, how much HCl is needed?
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Ratio: NaOH : HCl = 10 : 8 = 5 : 4
For 20 mL NaOH: HCl required = (8/10) × 20 = 16 mL
Answer: (d) 16 mL. Since the NaOH solution amount doubled (10→20 mL), the HCl required also doubles (8→16 mL).
Write balanced equations for: (a) dil. H₂SO₄ + Al; (b) dil. HCl + Fe filings; (c) NaHCO₃ heated.
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(b) 2HCl(aq) + Fe(s) → FeCl₂(aq) + H₂(g) — Fe=1=1✓, H=2=2✓, Cl=2=2✓
(c) 2NaHCO₃(s) →Heat Na₂CO₃(s) + H₂O(l) + CO₂(g) — Na=2=2✓, H=2=2✓, C=2=2✓, O=6=6✓
| 📝 Practice Set A — Multiple Choice Questions (8 Questions) |
(a) 1 (b) 4 (c) 5 (d) 10
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(a) NaCl (b) HCl (c) LiCl (d) KCl
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(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic
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(a) 1 molecule (b) 2 molecules (c) 5 molecules (d) 10 molecules
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(a) exactly 7 (b) above 7 (c) less than 5.6 (d) between 6 and 7
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(a) Dry NaCl (b) Dry NaOH (c) Dry slaked lime Ca(OH)₂ (d) Quick lime CaO
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(a) Rain water is basic (b) Rain water contains dissolved ions from gases (c) Rain water is a mixture (d) Distilled water is denser
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(a) Baking soda (b) Washing soda (c) Bleaching powder (d) Plaster of Paris
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| 📝 Practice Set B — Short Answer Questions (6 Questions) |
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Example 1: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
Example 2: Ca(OH)₂(aq) + H₂SO₄(aq) → CaSO₄(aq) + 2H₂O(l)
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Washing soda (Na₂CO₃·10H₂O): (1) Used in glass, soap, paper industries. (2) Removes permanent hardness of water; used as a cleaning agent at home.
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Onion: Strong onion smell is present in acid but disappears in base (NaOH destroys the odour-producing compounds). Vanilla: Pleasant vanilla smell disappears in basic solution. Both onion and vanilla are used as olfactory indicators when colour changes cannot be observed (e.g., in coloured solutions or for visually impaired students).
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Prevention: (1) Clean mouth/brush teeth after meals to remove food particles and acids. (2) Use basic toothpaste — the base neutralises the acids formed by bacteria: Acid + Base → Salt + Water. This raises pH above 5.5, preventing enamel corrosion.
| 📝 Practice Set C — Long Answer Questions (4 Questions) |
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1. Human Body: Body functions best at pH 7.0–7.8. Blood pH is ~7.4. Even slight changes can be fatal. Living organisms survive only within a narrow pH range.
2. Digestion: Stomach produces HCl (pH ~1.2) to digest food. Excess acid causes indigestion. Antacids (mild bases) neutralise excess acid and provide relief.
3. Tooth Decay: Bacteria produce acid from sugar. When mouth pH < 5.5, tooth enamel corrodes. Basic toothpaste neutralises acid and prevents decay.
4. Agriculture: Plants need specific pH for growth. Acidic soil (due to acid rain or chemical fertilisers) is treated with lime (CaO or Ca(OH)₂) to raise pH.
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2. Acid + Metal Carbonate → Salt + CO₂ + H₂O: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑ [CO₂ turns lime water milky]
3. Acid + Metal Hydrogencarbonate → Salt + CO₂ + H₂O: NaHCO₃ + HCl → NaCl + H₂O + CO₂↑
4. Acid + Base (Neutralisation) → Salt + H₂O: NaOH + HCl → NaCl + H₂O [pH 7 at endpoint]
5. Acid + Metal Oxide → Salt + H₂O: CuO + 2HCl → CuCl₂ + H₂O [black CuO → blue-green CuCl₂ solution]. Metallic oxides are basic oxides.
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(b) Baking Soda NaHCO₃: NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃. Mild non-corrosive basic salt. Uses: baking powder (CO₂ makes bread spongy: 2NaHCO₃ →Heat Na₂CO₃ + H₂O + CO₂); antacid (neutralises excess stomach acid); soda-acid fire extinguisher.
(c) Washing Soda Na₂CO₃·10H₂O: Heat NaHCO₃ → Na₂CO₃; add water: Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O. Uses: glass, soap, paper industries; manufacture of sodium compounds like borax; domestic cleaning agent; removes permanent hardness of water.
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Weak acids partially ionise: CH₃COOH ⇌ CH₃COO⁻ + H⁺ (partial). Weak acids: CH₃COOH, H₂CO₃, H₃PO₄.
Comparison: At the same molar concentration (e.g., 1M): 1M HCl has many more H⁺ ions than 1M CH₃COOH. HCl has a lower pH and reacts more vigorously with metals (Mg ribbon fizzes more in HCl). HCl conducts electricity better (more ions). The activity and reactivity of an acid directly depends on the concentration of H⁺ ions in solution — more H⁺ = more reactive/stronger acid.
| 📝 Practice Set D — Numerical / Equation Problems (4 Questions) |
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(b) 2Al(s) + 3H₂SO₄(aq) → Al₂(SO₄)₃(aq) + 3H₂(g) — Al=2=2✓, H=6=6✓, S=3=3✓, O=12=12✓. Displacement reaction; H₂ evolved.
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Na=2=2✓, H=2=2✓, C=2=2✓, O=6=6✓
Gas produced: CO₂ (carbon dioxide).
Test: Pass the gas through calcium hydroxide (lime water) — Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s)↓ + H₂O(l). Lime water turns milky white → confirms CO₂. On passing excess CO₂, white precipitate dissolves again (Ca(HCO₃)₂ forms).
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Plaster of Paris (white powder) absorbs water and sets into hard gypsum. This setting is irreversible — that is why it must be stored in moisture-proof containers.
It is called “Plaster of Paris” because large deposits of gypsum are found near Paris, France. The plaster was historically made there from local gypsum deposits, giving it the name.
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(b) Solution A (pH 6) is acidic (pH <7) — could be urine or milk. Solution B (pH 8) is basic/alkaline (pH >7) — could be sea water or egg white.
(c) If Solution B (basic) is diluted, water is added, which decreases OH⁻ concentration per unit volume. pH decreases (moves towards 7, neutral). Dilution of a basic solution moves its pH towards 7.
| 💡 Important Facts to Remember |
| 📚 Chapter Summary |
Chapter 2 — Acids, Bases and Salts: Key Points
| Acids Sour taste • Turn blue litmus red • pH <7 • Produce H⁺(aq)/H₃O⁺ in water • React with metals → H₂ • React with carbonates → CO₂ • React with bases → salt + water |
Bases/Alkalis Bitter taste • Soapy feel • Turn red litmus blue • pH >7 • Produce OH⁻(aq) in water • React with metals (Zn, Al) → H₂ • Alkalis = water-soluble bases |
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| pH Scale 0–14 range • pH 7 = neutral • pH <7 = acidic • pH >7 = alkaline • Universal indicator shows colours • H⁺ ↑ = pH ↓ |
Salts Strong acid + Strong base → neutral salt (pH 7) • Strong acid + Weak base → acidic salt • Weak acid + Strong base → basic salt |
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| 🏆 8-Point Exam Quick-Check |
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✅ Must-Know Facts
1. All acids produce H⁺(aq) in water; all bases produce OH⁻(aq). Water is essential for ionisation. 2. Neutralisation: H⁺(aq) + OH⁻(aq) → H₂O(l). Salt and water formed. 3. Chlor-alkali process gives three products: Cl₂ (anode), H₂ (cathode), NaOH (near cathode). 4. Tooth decay starts at pH < 5.5. Acid rain pH < 5.6. Body works at pH 7.0–7.8. 5. CO₂ test = lime water turns milky. H₂ test = burns with pop sound. |
⚠ Common Exam Traps
Trap 1: All alkalis are bases but NOT all bases are alkalis (only water-soluble ones). Trap 2: Dry HCl does NOT show acidic behaviour — water is essential for ionisation. Trap 3: Always add acid TO water (A to W), never water to acid — risk of splash/burns. Trap 4: Glucose and alcohol contain H but are NOT acids — they don’t produce H⁺ in water. Trap 5: Higher pH does NOT mean more H⁺ — it means LESS H⁺ (inverse relationship). |
This comprehensive study page for Class 10 Science Chapter 2 — Acids, Bases and Salts covers all CBSE and NCERT topics including properties of acids and bases, indicators, olfactory indicators, the pH scale, neutralisation reactions, the chlor-alkali process, bleaching powder, baking soda, washing soda, water of crystallisation, gypsum and Plaster of Paris. Includes 13 fully solved worked examples, 4 practice sets with answers, all 15 lab activities as interactive accordions, and HTML table diagrams of key experiments. Perfect for CBSE Class 10 board exam revision. Visit School Revise for more Grade 10 NCERT Science study materials.
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