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By rohit.pandey1
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Updated on 26 Jun 2026, 18:01 IST
Acids, Bases and Salts is Chapter 2 of NCERT Class 10 Science and an important Chemistry chapter for CBSE board exam preparation. This chapter explains the properties of acids and bases, their reactions with metals and carbonates, the use of indicators, the pH scale, neutralisation reactions, and the preparation and uses of important salts.
These Acids, Bases and Salts Class 10 Notes are written in a simple, exam-focused format to help students revise quickly. The notes cover acids, bases, salts, indicators, pH in daily life, strong and weak acids, chlor-alkali process, bleaching powder, baking soda, washing soda, plaster of Paris, and important board questions.
Students can use these notes for school exams, pre-board exams, Class 10 CBSE board revision, MCQs, previous year questions, case-based questions, and important long-answer questions.
In this chapter, students learn how acids, bases, and salts behave in daily life and in chemical reactions. It explains important concepts such as indicators, pH scale, neutralisation, reactions of acids and bases, and the preparation and uses of common salts like baking soda, washing soda, bleaching powder, and Plaster of Paris. This chapter is important for CBSE Class 10 exams because it includes several formula-based, reaction-based, and application-based questions.
| Topic | Key Learning |
| Acids | Substances that give H⁺ ions in aqueous solution |
| Bases | Substances that give OH⁻ ions in aqueous solution |
| Indicators | Substances used to identify acids and bases |
| pH Scale | Scale used to measure acidic, basic, or neutral nature |
| Neutralisation | Reaction between acid and base to form salt and water |
| Chlor-Alkali Process | Electrolysis of brine to form NaOH, Cl₂, and H₂ |
| Important Salts | Bleaching powder, baking soda, washing soda, and plaster of Paris |
| Daily-life Applications | Tooth decay, antacids, acid rain, soil treatment, and food preparation |
Students can download the Acids, Bases and Salts Class 10 Notes PDF for offline revision. The PDF includes definitions, formulas, chemical equations, tables, pH chart, important salts, MCQs, and exam-oriented questions.
Acids are substances that produce hydrogen ions, H⁺, in aqueous solution. They are generally sour in taste, turn blue litmus red, and react with metals, bases, metal carbonates, and metal hydrogen carbonates.
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| Acid | Formula | Found In |
| Hydrochloric acid | HCl | Stomach |
| Sulphuric acid | H₂SO₄ | Batteries |
| Nitric acid | HNO₃ | Laboratories |
| Acetic acid | CH₃COOH | Vinegar |
| Citric acid | C₆H₈O₇ | Lemon and orange |
| Lactic acid | C₃H₆O₃ | Curd |
| Tartaric acid | C₄H₆O₆ | Tamarind |
Bases are substances that produce hydroxide ions, OH⁻, in aqueous solution. Bases are bitter in taste, feel soapy, and turn red litmus blue. Water-soluble bases are called alkalis.
| Base | Formula | Common Use |
| Sodium hydroxide | NaOH | Soap making, paper industry |
| Potassium hydroxide | KOH | Batteries |
| Calcium hydroxide | Ca(OH)₂ | Whitewashing |
| Magnesium hydroxide | Mg(OH)₂ | Antacid |
| Ammonium hydroxide | NH₄OH | Cleaning agents |
| Basis | Acids | Bases |
| Ions produced in water | H⁺ ions | OH⁻ ions |
| Taste | Sour | Bitter |
| Touch | Not tested by touch for safety | Soapy feel |
| Litmus test | Blue litmus turns red | Red litmus turns blue |
| pH value | Less than 7 | More than 7 |
| Example | HCl, H₂SO₄, CH₃COOH | NaOH, KOH, Ca(OH)₂ |
Indicators are substances that show different colours in acidic and basic solutions. They help identify whether a given substance is acidic, basic, or neutral.
Indicators are important in Class 10 Chemistry because many exam questions ask students to identify acids and bases using litmus, methyl orange, phenolphthalein, universal indicator, or olfactory indicators.
| Indicator | In Acidic Solution | In Basic Solution | In Neutral Solution |
| Blue litmus | Turns red | No change | No change |
| Red litmus | No change | Turns blue | No change |
| Methyl orange | Red | Yellow | Orange |
| Phenolphthalein | Colourless | Pink | Colourless |
| Universal indicator | Red/orange/yellow | Blue/violet | Green |
Olfactory indicators are substances whose smell changes in acidic or basic solutions. These indicators are useful because they help identify acids and bases through change in odour.
| Olfactory Indicator | Behaviour |
| Onion | Smell changes in basic solution |
| Vanilla essence | Smell disappears in basic solution |
| Clove oil | Smell changes in acidic or basic medium |
Dry HCl gas does not change the colour of dry litmus paper because it does not release H⁺ ions in the absence of water. Acidic behaviour is shown only when hydrogen ions are produced in aqueous solution. Therefore, dry HCl gas does not show acidic properties on dry litmus paper.
Hydrogen chloride gas dissolves in water to form hydrochloric acid.
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HCl + H₂O → H₃O⁺ + Cl⁻
The hydronium ions, H₃O⁺, are responsible for the acidic nature of hydrochloric acid.
Remember:
Acids show acidic properties only in the presence of water.
Acid should always be added slowly to water because dilution of concentrated acid is highly exothermic. If water is added directly to concentrated acid, a large amount of heat may be released suddenly, causing the mixture to splash. Adding acid to water allows heat to spread more safely.
Always add acid to water slowly with constant stirring. Never add water to concentrated acid.
Acids show important chemical reactions with metals, metal carbonates, metal hydrogen carbonates, bases, and metal oxides.
Acids react with metals to produce salt and hydrogen gas.
Acid + Metal → Salt + Hydrogen gas
Zn + 2HCl → ZnCl₂ + H₂
Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas.
Hydrogen gas burns with a pop sound when a burning candle is brought near it.
Acids react with metal carbonates to form salt, water, and carbon dioxide gas.
Acid + Metal carbonate → Salt + Water + Carbon dioxide
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
Sodium carbonate reacts with hydrochloric acid to form sodium chloride, water, and carbon dioxide.
Acids react with metal hydrogen carbonates to form salt, water, and carbon dioxide gas.
Acid + Metal hydrogen carbonate → Salt + Water + Carbon dioxide
NaHCO₃ + HCl → NaCl + H₂O + CO₂
Sodium hydrogen carbonate reacts with hydrochloric acid to form sodium chloride, water, and carbon dioxide.
Carbon dioxide gas turns lime water milky due to the formation of calcium carbonate.
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
When excess carbon dioxide is passed, the milkiness disappears due to the formation of calcium hydrogen carbonate.
CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂
Acids react with bases to form salt and water. This reaction is called neutralisation.
Acid + Base → Salt + Water
HCl + NaOH → NaCl + H₂O
Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water.
Metal oxides are basic in nature. They react with acids to form salt and water.
Acid + Metal oxide → Salt + Water
CuO + 2HCl → CuCl₂ + H₂O
Copper oxide reacts with hydrochloric acid to form copper chloride and water.
Bases react with acids, non-metal oxides, and some metals. They turn red litmus blue and produce OH⁻ ions in aqueous solution.
Bases react with acids to form salt and water.
NaOH + HCl → NaCl + H₂O
This is a neutralisation reaction.
Non-metal oxides are acidic in nature. They react with bases to form salt and water.
2NaOH + CO₂ → Na₂CO₃ + H₂O
Sodium hydroxide reacts with carbon dioxide to form sodium carbonate and water.
Some metals react with strong bases to form salt and hydrogen gas.
2NaOH + Zn → Na₂ZnO₂ + H₂
Zinc reacts with sodium hydroxide to form sodium zincate and hydrogen gas.
Acids and bases conduct electricity in aqueous solution because they produce ions. Acids produce H⁺ or H₃O⁺ ions, while bases produce OH⁻ ions. These ions move through the solution and carry electric current.
HCl → H⁺ + Cl⁻
NaOH → Na⁺ + OH⁻
Distilled water does not conduct electricity because it contains almost no dissolved ions. Rainwater conducts electricity because it dissolves gases and salts from the atmosphere, forming ions in solution. These ions allow electric current to pass through rainwater.
Strong acids and bases ionise almost completely in water, while weak acids and bases ionise only partially. This difference affects their pH value, conductivity, and reactivity.
| Type | Meaning | Examples |
| Strong acid | Completely ionises in water | HCl, H₂SO₄, HNO₃ |
| Weak acid | Partially ionises in water | CH₃COOH, citric acid |
| Strong base | Completely ionises in water | NaOH, KOH |
| Weak base | Partially ionises in water | NH₄OH, Mg(OH)₂ |
The pH scale is used to measure how acidic or basic a solution is. It generally ranges from 0 to 14. A solution with pH less than 7 is acidic, pH equal to 7 is neutral, and pH greater than 7 is basic.
| pH Range | Nature of Solution | Example |
| 0–3 | Strongly acidic | HCl |
| 4–6 | Weakly acidic | Lemon juice, vinegar |
| 7 | Neutral | Pure water |
| 8–10 | Weakly basic | Baking soda solution |
| 11–14 | Strongly basic | NaOH solution |
The pH scale is important in daily life because many biological, agricultural, and environmental processes depend on pH. The human body, soil, mouth, stomach, and aquatic life all need a suitable pH range to function properly.
The stomach produces hydrochloric acid, HCl, which helps digest food and kills harmful microbes. However, excess acid may cause acidity and discomfort. Antacids such as magnesium hydroxide neutralise excess acid in the stomach.
Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O
Tooth decay starts when the pH of the mouth falls below 5.5. Bacteria in the mouth break down sugar and produce acids. These acids corrode tooth enamel, which is mainly made of calcium compounds. Basic toothpaste helps neutralise the excess acid and prevents tooth decay.
Always mention pH below 5.5 when writing an answer on tooth decay.
Rainwater becomes acidic when gases like sulphur dioxide and nitrogen oxides dissolve in it. If the pH of rainwater falls below 5.6, it is called acid rain. Acid rain can damage plants, soil, aquatic life, buildings, and monuments.
Plants grow best in a specific pH range. If soil is too acidic or too basic, plant growth is affected. Farmers may add suitable substances to adjust the soil pH.
| Soil Condition | Treatment |
| Too acidic | Add quicklime, slaked lime, or chalk |
| Too basic | Add organic matter or compost |
Living organisms are sensitive to pH changes. Aquatic animals may not survive if the pH of water changes sharply. Plants also need a proper soil pH for healthy growth.
Salts are ionic compounds formed when the hydrogen ions of an acid are replaced by metal ions or ammonium ions. Salts are commonly formed during neutralisation reactions between acids and bases.
HCl + NaOH → NaCl + H₂O
Here, sodium chloride, NaCl, is the salt formed.
Salts that contain the same positive ion or negative ion are said to belong to the same family.
| Salt Family | Common Ion | Examples |
| Sodium salts | Na⁺ | NaCl, Na₂SO₄, NaNO₃ |
| Chloride salts | Cl⁻ | NaCl, KCl, CaCl₂ |
| Sulphate salts | SO₄²⁻ | Na₂SO₄, CuSO₄, CaSO₄ |
| Nitrate salts | NO₃⁻ | NaNO₃, KNO₃ |
The pH of a salt depends on the acid and base from which it is formed.
| Acid Used | Base Used | Nature of Salt | Example |
| Strong acid | Strong base | Neutral | NaCl |
| Strong acid | Weak base | Acidic | NH₄Cl |
| Weak acid | Strong base | Basic | CH₃COONa |
| Weak acid | Weak base | Depends on relative strength | NH₄CH₃COO |
Ammonium chloride, NH₄Cl, is formed from a strong acid, HCl, and a weak base, NH₄OH, so its solution is acidic. Sodium acetate, CH₃COONa, is formed from a weak acid, CH₃COOH, and a strong base, NaOH, so its solution is basic.
Common salt, sodium chloride, NaCl, is an important raw material for many useful chemicals. Important products obtained from common salt include sodium hydroxide, bleaching powder, baking soda, washing soda, and plaster of Paris.
The chlor-alkali process is the electrolysis of brine, which is a concentrated solution of sodium chloride. This process produces sodium hydroxide, chlorine gas, and hydrogen gas. It is called chlor-alkali because chlorine and an alkali, sodium hydroxide, are formed.
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
| Location | Product Formed | Formula |
| At anode | Chlorine gas | Cl₂ |
| At cathode | Hydrogen gas | H₂ |
| Near cathode | Sodium hydroxide solution | NaOH |
| Product | Uses |
| Chlorine gas, Cl₂ | Water treatment, disinfectants, PVC, bleaching powder |
| Hydrogen gas, H₂ | Fuels, margarine, ammonia production |
| Sodium hydroxide, NaOH | Soap, paper, textiles, detergents, cleaning agents |
Sodium hydroxide, NaOH, is a strong base produced during the chlor-alkali process. It is also known as caustic soda.
Bleaching powder is calcium oxychloride. Its chemical formula is CaOCl₂. It is prepared by passing chlorine gas over dry slaked lime.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Baking soda is sodium hydrogen carbonate. Its chemical formula is NaHCO₃. It is a mild base and is commonly used in cooking, antacids, and fire extinguishers.
NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
Baking soda is pure sodium hydrogen carbonate, NaHCO₃. Baking powder is a mixture of baking soda and a mild edible acid such as tartaric acid. When baking powder is mixed with water or heated, it releases carbon dioxide, which makes cakes and bread soft and spongy.
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Carbon dioxide gas helps dough rise.
Tartaric acid neutralises sodium carbonate formed during heating. Without tartaric acid, sodium carbonate may give a bitter taste to food.
Washing soda is sodium carbonate decahydrate. Its chemical formula is Na₂CO₃·10H₂O. It is used in cleaning, softening hard water, and in the glass, soap, and paper industries.
Sodium carbonate is obtained by heating baking soda.
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Sodium carbonate is then crystallised with water to form washing soda.
Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O
Plaster of Paris is calcium sulphate hemihydrate. Its chemical formula is CaSO₄·½H₂O. It is prepared by heating gypsum at 373 K.
CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
Gypsum → Plaster of Paris + Water
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
Plaster of Paris changes back into gypsum when mixed with water.
Plaster of Paris should be stored in a moisture-proof container because it reacts with water and changes back into gypsum. If it absorbs moisture from air, it hardens and becomes useless for making casts, moulds, and decorative items.
| Compound | Chemical Name | Formula | Preparation | Uses |
| Sodium hydroxide | Caustic soda | NaOH | Electrolysis of brine | Soap, paper, detergents |
| Bleaching powder | Calcium oxychloride | CaOCl₂ | Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O | Bleaching, disinfecting water |
| Baking soda | Sodium hydrogen carbonate | NaHCO₃ | NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃ | Baking, antacid, fire extinguisher |
| Washing soda | Sodium carbonate decahydrate | Na₂CO₃·10H₂O | Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O | Cleaning, softening water |
| Plaster of Paris | Calcium sulphate hemihydrate | CaSO₄·½H₂O | Heating gypsum at 373 K | Casts, moulds, toys |
| Reaction | Balanced Equation |
| Acid + metal | Zn + 2HCl → ZnCl₂ + H₂ |
| Acid + carbonate | Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ |
| Acid + hydrogen carbonate | NaHCO₃ + HCl → NaCl + H₂O + CO₂ |
| Neutralisation | HCl + NaOH → NaCl + H₂O |
| Acid + metal oxide | CuO + 2HCl → CuCl₂ + H₂O |
| Base + non-metal oxide | 2NaOH + CO₂ → Na₂CO₃ + H₂O |
| Chlor-alkali process | 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ |
| Bleaching powder | Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O |
| Heating baking soda | 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ |
| Washing soda formation | Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O |
| POP preparation | CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O |
| POP with water | CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O |
| Common Mistake | Correct Concept |
| Writing acids show acidic nature without water | Acids show acidic nature in aqueous solution due to H⁺ or H₃O⁺ ions |
| Adding water to acid | Always add acid to water slowly |
| Confusing anode and cathode in chlor-alkali process | Chlorine forms at anode; hydrogen forms at cathode |
| Writing baking soda and baking powder as same | Baking soda is NaHCO₃; baking powder contains baking soda and edible acid |
| Forgetting pH 5.5 in tooth decay | Tooth decay starts when mouth pH falls below 5.5 |
| Confusing washing soda and baking soda | Washing soda is Na₂CO₃·10H₂O; baking soda is NaHCO₃ |
| Writing wrong formula of Plaster of Paris | Correct formula is CaSO₄·½H₂O |
| Not mentioning moisture-proof storage of POP | POP reacts with moisture and becomes gypsum |
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Dry HCl gas does not change dry litmus paper because it does not release H⁺ ions without water. Acids show acidic properties only in aqueous solution. When HCl dissolves in water, it produces H₃O⁺ ions, which turn blue litmus red.
Acid should be added slowly to water because dilution of concentrated acid is highly exothermic. If water is added directly to acid, heat may be released suddenly and the acid may splash. Adding acid to water helps heat spread more safely.
The chlor-alkali process is the electrolysis of brine, a concentrated sodium chloride solution. It produces chlorine gas at the anode, hydrogen gas at the cathode, and sodium hydroxide near the cathode. The overall reaction is 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂.
Baking soda is pure sodium hydrogen carbonate, NaHCO₃. Baking powder is a mixture of baking soda and a mild edible acid such as tartaric acid. Baking powder releases CO₂ during heating, making cakes and bread soft and spongy.
Tooth decay begins when the pH of the mouth falls below 5.5. Bacteria break down sugar and produce acids, which attack tooth enamel. Basic toothpaste helps neutralise the excess acid and protects teeth from decay.
Plaster of Paris is stored in a moisture-proof container because it reacts with water and changes into gypsum. If it absorbs moisture from air, it hardens and becomes useless for making casts, moulds, and decorative items.
Olfactory indicators are substances whose smell changes in acidic or basic solutions. Examples include onion, vanilla essence, and clove oil. They help identify acids and bases through change in odour.
Distilled water does not conduct electricity because it has almost no dissolved ions. Rainwater dissolves gases and salts from the atmosphere, forming ions. These ions allow rainwater to conduct electricity.
The chemical formula of bleaching powder is CaOCl₂. It is prepared by passing chlorine gas over dry slaked lime. It is used for bleaching and disinfecting drinking water.
The chemical formula of washing soda is Na₂CO₃·10H₂O. Its chemical name is sodium carbonate decahydrate. It is used as a cleaning agent and for removing permanent hardness of water.