NCERT Question and Answer for Class 10 Science Chapter 2 Acids, Bases and Salts

 Let's dive into the exciting world of Chapter 2 - Acids, Bases and Salts from your Class 10 Science NCERT book.

This chapter is all about three cool things in chemistry: acids, bases, and salts.

Acids: These are like the sour stuff, such as lemon juice or vinegar. They can make blue paper turn red and are pretty strong sometimes.

Bases: Bases are different. They taste bitter and feel slippery, like soap. They can turn red paper blue and can neutralize acids.

Salts: When acids and bases have a chat, they make a new thing called salts. Think of table salt - it's one kind of salt. But there are lots of other types, too!

We'll learn about how these things work, what they do, and why they're important. So, get ready to explore the exciting world of acids, bases, and salts!

 

Introduction to Acids, Bases and Salts

Acids and bases are two fundamental categories of substances in chemistry that play crucial roles in various natural processes and everyday life. Understanding these substances is essential for comprehending a wide range of chemical reactions and their implications.
 

Acids:
Acids are substances that ionize in water to produce hydrogen ions H+. They are characterized by their sour taste, ability to turn blue litmus paper red, and their corrosive nature. Common examples of acids include citric acid (found in citrus fruits), hydrochloric acid (found in the stomach), and sulfuric acid (used in car batteries).
 

Bases:
Bases, on the other hand, are substances that ionize in water to produce hydroxide ions OH−. They often have a bitter taste, feel slippery to the touch, and turn red litmus paper blue. Examples of bases include sodium hydroxide (used in cleaning agents), ammonia (found in household cleaners), and calcium hydroxide (used in cement).
 

Salts: Salts are chemical compounds composed of positively charged ions (called cations) and negatively charged ions (called anions). They are formed through a reaction between an acid and a base, known as a neutralization reaction.

Neutralization Reaction:
When an acid reacts with a base, they undergo a chemical reaction known as neutralization. In this reaction, the hydrogen ions from the acid combine with the hydroxide ions from the base to form water (${𝐻}_2𝑂$). The remaining ions form a salt. For example, when hydrochloric acid$𝐻𝐶𝑙$) reacts with sodium hydroxide ($𝑁𝑎𝑂𝐻$), the products are water and sodium chloride ($𝑁𝑎𝐶𝑙$)
 

pH Scale:
The strength of an acid or base is measured on the pH scale, which ranges from 0 to 14. A pH of 7 is considered neutral, indicating a balance between acidity and basicity. pH values below 7 indicate acidity, with lower values indicating stronger acids. pH values above 7 indicate basicity, with higher values indicating stronger bases.

Understanding the properties and behavior of acids and bases is crucial for various scientific disciplines, including chemistry, biology, and environmental science. In the next sections, we will delve deeper into the properties, classification, and real-world applications of acids and bases. 

Let’s move on to the NCERT Question and Answer section for Chapter 2. Feel free to let me know if you have specific questions or if you'd like a variety of questions and answers.

 NCERT Class 10 Science – Page 18

Q1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube ?

Ans: To identify the contents of each test tube using only red litmus paper:

1. Dip the red litmus paper into the first test tube with distilled water. If it remains red, it's neutral.

2. Dip the same red litmus paper into the second test tube with the acidic solution. If it turns blue, it's acidic.

3. Dip the red litmus paper into the third test tube with the basic solution. If it remains red, it's basic.

This method quickly distinguishes between neutral, acidic, and basic solutions based on the color changes of the red litmus paper. 

 NCERT Class 10 Science – Page 22

Q1.  Why should curd and sour substances not be kept in brass and copper vessels ?

Ans: Curd and sour substances should not be stored in brass and copper vessels because they can cause a reaction with the metals, making the food unsafe to eat. It's best to use pots and containers made from materials like stainless steel or glass to avoid any health risks.

 Q2. Which gas is usually liberated when an acid reacts with a metal ? Illustrate with an example. How will you test for the presence of this gas ? 

Ans: When an acid reacts with a metal, hydrogen gas (${𝐻}_2$) is usually liberated. This reaction is a type of single displacement reaction, where the metal displaces the hydrogen from the acid, forming a metal salt and releasing hydrogen gas.

An example:

$\text{Zinc (metal)}+\text{Hydrochloric acid}\to \text{Zinc chloride (salt)}+\text{Hydrogen gas}$

 Zn+2HCl→ZnCl2​+H2​

 

To test for the presence of hydrogen gas, you can perform the following steps:

1. Place a burning splint near the mouth of the test tube containing the reaction mixture (acid and metal).
2. If hydrogen gas is present, it will ignite with a 'pop' sound when it comes into contact with the flame of the burning splint.
3. The 'pop' sound indicates the presence of hydrogen gas, confirming that the acid-metal reaction has occurred.

Q3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Ans: The balanced chemical equation for the reaction between metal compound A and dilute hydrochloric acid, where one of the compounds formed is calcium chloride, is:

$\text{Metal compound A}+2\text{HCl}\to \text{Calcium chloride}+\text{Hydrogen gas}$

$\text{A}+2\text{HCl}\to {\text{CaCl}}_2+{\text{H}}_2$

This reaction produces effervescence, indicating the release of gas (hydrogen), which extinguishes a burning candle when it comes into contact with it.

  NCERT Class 10 Science – Page 25

Q1. Why do HCl, HNO₃, etc show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character ? 

Ans: HCl, HNO3, etc., show acidic properties in water because they release hydrogen ions (\(H^+\)). This makes the solution acidic. Compounds like alcohol and glucose don't release hydrogen ions in water, so they don't exhibit acidic behavior.  

Q2. Why does an aqueous solution of an acid conduct electricity ?

Ans: An aqueous solution of an acid conducts electricity because it contains ions that can move freely, allowing electric current to flow through the solution. 

Q3. Why does dry HCl gas not change the colour of the dry litmus paper ? 

Ans:  Dry HCl gas doesn't affect the color of dry litmus paper because it doesn't have the substances needed to make the paper change color.