KEY NOTES -Class 10 – Science -Chemistry -chapter 2- Acids, Bases and Salt

KEY NOTES -Class 10 – Science -Chemistry -chapter 2- Acids, Bases and Salt

Introduction:

• Acids, bases, and salts are three categories of compounds with distinct properties and behaviours.
• Acids are substances that release hydrogen ions(H⁺). when dissolved in water.
• Bases are substances that release hydroxide ions (OH^–) in aqueous solutions.
• Salts are ionic compounds formed by the combination of a positive ion (from a base) and a negative ion (from an acid).

A substance that tastes sour in water, turns blue litmus red, and neutralises the bases is known as an acid. If a substance’s aqueous solution tastes bitter, turns red litmus blue, or neutralises acids, it’s called a base. Salt is a neutral material that has no effect on litmus in an aqueous solution.

Chemical Properties of Acids and Bases

Acid + Metal → Salt + Hydrogen (Refer activity 2.3 on page No. 19 of NCERT Book)

2HCl + Zn → ZnCl2 + H2

2HNO3 + Zn → Zn (NO3 ) 2 + H2

 H2 SO4 + Zn→ ZnSO4 + H2

2CH3COOH + Zn → (CH3COO)2 Zn + H2

How do acids and bases react with each other

Acids and bases can react with each other in a chemical process known as neutralization. In a neutralization reaction, an acid reacts with a base to produce water and a salt. The overall result is a solution that is neither acidic nor basic but neutral.

The general chemical equation for a neutralization reaction is:

Acids + bases à water + salts

Neutralization reactions are not limited to hydrochloric acid and sodium hydroxide; they can involve various acids and bases. The key is that the hydrogen ions from the acid react with the hydroxide ions from the base to form water, and the remaining ions combine to create a salt. This type of reaction is essential in various applications, including in the pharmaceutical, food, and environmental industries.

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Properties of Acids: 

• Sour taste.
• Turn blue litmus paper red.
• Conduct electricity in aqueous solution.
• React with metals to produce hydrogen gas.

Examples of Acids:

Hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and citric acid.

Some naturally occurring acids: 

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Properties of Bases:

• Bitter taste.
• Slippery or soapy feel.
• Turn red litmus paper blue.
• Conduct electricity in aqueous solution.

Examples of Bases:

Sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH₃).

What do all acids and all bases have in common

Acids and bases are two distinct types of chemical substances with unique properties, but they do share some common characteristics:

Similarities Between Acids and Bases:

Ionization in Water:

Both acids and bases undergo ionization when dissolved in water. Acids release hydrogen ions (H+ ), while bases release hydroxide ions (OH− ).

Conductivity:

Aqueous solutions of both acids and bases conduct electricity. This is due to the presence of ions (either H+ or OH− ) in the solution that can carry an electric current.

Chemical Reactivity:

Acids and bases are chemically reactive. Acids react with metals to produce hydrogen gas, while bases can react with certain fats and oils in a process called saponification.

Neutralization Reaction:

Acids and bases can neutralize each other in a chemical reaction known as neutralization. In this process, the hydrogen ions from the acid combine with the hydroxide ions from the base to form water, and the remaining ions combine to form a salt.

Differences Between Acids and Bases:

Hydrogen Ion vs. Hydroxide Ion:

The fundamental difference lies in the ions they release in water. Acids release

H+  ions, while bases release OH−  ions.

Litmus Paper Test:

Acids turn blue litmus paper red, while bases turn red litmus paper blue.

Taste:

Acids generally have a sour taste (e.g., citric acid in lemons), while bases have a bitter taste (e.g., baking soda).

Feel:

Acids do not have a distinctive feel, while bases can feel slippery or soapy.

pH Range:

Acids have a pH less than 7, with lower pH values indicating stronger acidity. Bases have a pH greater than 7, with higher pH values indicating stronger basicity.

While acids and bases have distinct properties, their commonality lies in their behaviour in aqueous solutions and their ability to conduct electricity. Understanding these shared characteristics helps in comprehending their roles in various chemical reactions and applications.

Note : Non Metallic oxides are said to be acidic in nature because on reacting with a base they produce Salt and Water.

All acidic solutions conduct electricity.