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Class 10 · Chapter 2 · Chemistry

Acids, Bases and Salts Cheat Sheet

Reactions

Acid with a metal

Zn+2 HCl→ZnClX2+HX2↑\ce{Zn + 2HCl -> ZnCl2 + H2 ^}

Zinc displaces hydrogen from hydrochloric acid; hydrogen gas (↑) is evolved.

Base with a metal

2 NaOH+Zn→NaX2ZnOX2+HX2↑\ce{2NaOH + Zn -> Na2ZnO2 + H2 ^}

Zinc also reacts with sodium hydroxide (a base) to release hydrogen gas.

Acid with a metal carbonate

NaX2COX3+2 HCl→2 NaCl+HX2O+COX2↑\ce{Na2CO3 + 2HCl -> 2NaCl + H2O + CO2 ^}

Carbon dioxide gas (↑) is released; it turns lime water milky.

Acid with a metal hydrogencarbonate

NaHCOX3+HCl→NaCl+HX2O+COX2↑\ce{NaHCO3 + HCl -> NaCl + H2O + CO2 ^}

Baking soda with acid gives brisk effervescence of carbon dioxide.

Neutralisation

NaOH+HCl→NaCl+HX2O\ce{NaOH + HCl -> NaCl + H2O}

Base + acid → salt + water; heat is also produced.

Metal oxide with an acid

CuO+2 HCl→CuClX2+HX2O\ce{CuO + 2HCl -> CuCl2 + H2O}

Black copper oxide dissolves to give a blue-green solution of copper chloride.

Non-metal oxide with a base

COX2+Ca(OH)X2→CaCOX3↓+HX2O\ce{CO2 + Ca(OH)2 -> CaCO3 v + H2O}

Carbon dioxide turns lime water milky due to a white precipitate (↓) of calcium carbonate.

Chlor-alkali process

2 NaCl+2 HX2O→electricity2 NaOH+ClX2↑+HX2↑\ce{2NaCl + 2H2O ->[electricity] 2NaOH + Cl2 ^ + H2 ^}

Electrolysis of brine gives sodium hydroxide, chlorine (at the anode) and hydrogen (at the cathode).

Preparation of baking soda

NaCl+HX2O+COX2+NHX3→NHX4Cl+NaHCOX3\ce{NaCl + H2O + CO2 + NH3 -> NH4Cl + NaHCO3}

Sodium hydrogencarbonate (baking soda) is formed along with ammonium chloride.

Heating of baking soda

2 NaHCOX3→ΔNaX2COX3+HX2O+COX2↑\ce{2NaHCO3 ->[\Delta] Na2CO3 + H2O + CO2 ^}

On heating, baking soda gives washing soda, water and carbon dioxide.

Preparation of bleaching powder

Ca(OH)X2+ClX2→CaOClX2+HX2O\ce{Ca(OH)2 + Cl2 -> CaOCl2 + H2O}

Chlorine is passed over dry slaked lime to give bleaching powder.

Definitions

Acid
A substance that gives hydrogen ions (H⁺) in aqueous solution and turns blue litmus red.
Base
A substance that gives hydroxide ions (OH⁻) in aqueous solution and turns red litmus blue.
Alkali
A base that is soluble in water.
Indicator
A substance that changes colour in acidic or basic solutions.
Olfactory indicator
A substance whose smell changes in acidic or basic media, e.g. onion and vanilla essence.
Neutralisation
The reaction of an acid with a base to give a salt and water.
Salt
A compound formed when the hydrogen of an acid is replaced by a metal.
Water of crystallisation
The fixed number of water molecules present in one formula unit of a salt; e.g. CuSO₄·5H₂O.
Strong acid
An acid that ionises completely in water and releases a large amount of H⁺; e.g. HCl, H₂SO₄.
Weak acid
An acid that ionises only partially in water; e.g. acetic acid, carbonic acid.
pH
A scale from 0 to 14 that measures how acidic or basic a solution is.

Key Points

  • pH scale: pH < 7 acidic, pH = 7 neutral and pH > 7 basic. As H⁺ concentration increases, pH decreases.
  • Litmus: acids turn blue litmus red; bases turn red litmus blue.
  • Phenolphthalein is colourless in acid and pink in base; methyl orange is red in acid and yellow in base.
  • Turmeric turns from yellow to red in a basic solution.
  • Strong acids: HCl, H₂SO₄, HNO₃. Weak acids: acetic acid, carbonic acid, citric acid, oxalic acid.
  • Metal oxides are basic; non-metal oxides are acidic. Aluminium oxide and zinc oxide are amphoteric.
  • The pH of blood is about 7.35–7.45; tooth decay begins below pH 5.5; acid rain has pH less than 5.6.
  • Common salts: common salt (NaCl), baking soda (NaHCO₃), washing soda (Na₂CO₃·10H₂O), bleaching powder (CaOCl₂) and plaster of Paris (CaSO₄·½H₂O).
  • Plaster of Paris is made by heating gypsum (CaSO₄·2H₂O) to 373 K; it hardens on mixing with water.
  • Hydrated copper sulphate (blue vitriol, CuSO₄·5H₂O) loses its water of crystallisation on heating and turns white.