CBSE – 10th Standard Science

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Class 10 chapter 2 – Acids, Bases and Salts

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Indicators tell us whether a substance is acidic or basic by change in colour. There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators.

CHEMICAL PROPERTIES OF ACIDS

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CHEMICAL PROPERTIES OF BASES

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REACTION OF ACIDS AND BASES WITH METALS

Reaction of acids with metals

the metal in the above reactions displaces hydrogen from the acids. This is seen as hydrogen gas. The metal combines with the remaining part of the acid and forms a compound called a salt. Thus,the reaction of a metal with an acid can be summarised as –

Acid + Metal → Salt + Hydrogen gas

Reaction of base with metal

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Reaction of Metal carbonates and Metal Hydrogencarbonates with Acids

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Reaction of Acids and Bases with each other

NEUTRALIZATION REACTION

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Reaction of Metallic Oxides with Acids

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 Acid or  Base in a Water Solution

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Bases generate hydroxide (OH–) ions in water. Bases which are soluble in water are called alkalis pH

A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German,meaning power.

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Sodium hydroxide

When electricity is passed through an aqueous solution of sodium

chloride (called brine), it decomposes to form sodium hydroxide. The

process is called the chlor-alkali process because of the products formed–

chlor for chlorine and alkali for sodium hydroxide.

2NaCl(aq) + 2H2O(l) →2NaOH(aq) + Cl2(g) + H2(g

Bleaching powder

Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2]. Bleaching powder is represented as CaOCl2

Ca(OH)2 + Cl2 →CaOCl2 + H2O

Baking soda

The chemical name of the compound is sodium hydrogencarbonate (NaHCO3). It is produced using sodium chloride as one of the raw materials.

NaCl + H2O + CO2 + NH3à NH4Cl + NaHCO3  

Washing soda

Another chemical that can be obtained from sodium chloride is

Na2CO3.10H2O (washing soda). Sodium carbonate can be obtained by heating baking soda; recrystallisation of sodium carbonate gives washing soda. It is also a basic salt.

Water of crystallisation

is the fixed number of water molecules present in one formula unit of a salt. Five water molecules are present in one formula unit of copper sulphate. Chemical formula for hydrated copper sulphate is CuSO4.5H2O. Similarly the molecule of Na2CO3.10H2O is wet.

One other salt, which possesses water of crystallisation is gypsum.

It has two water molecules as water of cyrstallisation. It has the formula CaSO4.2H2O. On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate

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