What is Acids, Bases and Salts Class 10: Complete Guide

Definition and Characteristics of Acids

Acids are substances that release hydrogen ions ($H^+$) when dissolved in water. They have a sour taste and can turn blue litmus paper red. Common examples include hydrochloric acid ($HCl$), sulfuric acid ($H_2SO_4$), and citric acid.

Key properties of acids:

• Sour taste
• Corrosive in concentrated form
• Conduct electricity in aqueous solution
• React with metals to produce hydrogen gas

Example: When hydrochloric acid dissolves in water:

$$HCl \rightarrow H^+ + Cl^-$$

This release of $H^+$ ions is what makes the solution acidic.

Definition and Characteristics of Bases

Bases are substances that release hydroxide ions ($OH^-$) in water. They taste bitter and feel slippery or soapy to touch. Bases turn red litmus paper blue.

Common bases: sodium hydroxide ($NaOH$), potassium hydroxide ($KOH$), and calcium hydroxide ($Ca(OH)_2$).

Key properties of bases:

• Bitter taste
• Slippery texture
• Conduct electricity when dissolved in water
• React with acids to form salts and water

Example: Sodium hydroxide dissociates in water as:

$$NaOH \rightarrow Na^+ + OH^-$$

Understanding Salts and Their Formation

Salts are ionic compounds formed when an acid reacts with a base in a neutralisation reaction. They consist of positive ions (from the base) and negative ions (from the acid).

General neutralisation reaction:

$$\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$$

Example: When hydrochloric acid reacts with sodium hydroxide:

$$HCl + NaOH \rightarrow NaCl + H_2O$$

Here, sodium chloride ($NaCl$) is the salt formed, and water is the byproduct.

Salts have various uses, such as in cooking (table salt), medicine, and industry.

The pH Scale: Measuring Acidity and Alkalinity

The pH scale measures how acidic or basic a solution is, ranging from 0 to 14.

• pH less than 7: Acidic solution
• pH equal to 7: Neutral solution
• pH greater than 7: Basic (alkaline) solution

Examples:

• Lemon juice has pH around 2 (acidic)
• Pure water has pH 7 (neutral)
• Soap solution has pH around 12 (basic)

Importance: The pH scale helps in identifying substances and understanding their chemical behaviour.

Indicators: Identifying Acids and Bases

Indicators are substances that change colour in acidic or basic solutions. They help us identify whether a solution is acidic or basic.

Common indicators:

• Litmus paper: Red in acid, blue in base
• Phenolphthalein: Colourless in acid, pink in base
• Methyl orange: Red in acid, yellow in base

Example: If a solution turns blue litmus paper red, it is acidic. This simple test is widely used in labs and schools.

Using indicators is essential for experiments and practical exams in Class 10 Science.

Common Reactions Involving Acids, Bases, and Salts

Several important chemical reactions involve acids, bases, and salts:

1. Neutralisation Reaction: Acid + Base → Salt + Water

Example: $$H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O$$

2. Reaction with Metals: Acids react with metals to produce hydrogen gas.

Example: $$2HCl + Zn \rightarrow ZnCl_2 + H_2$$

3. Reaction with Carbonates: Acids react with carbonates to produce salt, water, and carbon dioxide.

Example: $$2HCl + CaCO_3 \rightarrow CaCl_2 + H_2O + CO_2$$

These reactions are important for understanding chemical behaviour and are frequently asked in exams.