CBSE Class 7 Science Acid Bases and Salts Worksheet Set A - Free Printable

Problem Analysis:

The task involves two sections:
1. Fill in the blanks related to acids, bases, and salts.
2. True/False questions about the properties of acids, bases, and indicators.

Let's solve each section step by step.

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Section 1: Fill in the Blanks

#### i. Change of colour in an acid and a base depends on the type of the indicator.
- Explanation: Indicators are substances that change color in the presence of acids or bases. The specific color change depends on the type of indicator used (e.g., litmus paper, phenolphthalein).

#### ii. Acid turns blue litmus red.
- Explanation: Blue litmus paper is used as an indicator for acids. When an acid is added, it turns red.

#### iii. Bases turn red litmus blue.
- Explanation: Red litmus paper is used as an indicator for bases. When a base is added, it turns blue.

#### iv. Litmus has a mauve (purple) colour in distilled water.
- Explanation: Distilled water is neutral (neither acidic nor basic). In a neutral solution, litmus paper retains its original color, which is mauve or purple.

#### v. In neutralisation reaction a new substance is formed. This is called salt.
- Explanation: A neutralization reaction occurs when an acid reacts with a base to form salt and water. The resulting salt is a new substance.

#### vi. Lemon juice is acidic in nature.
- Explanation: Lemon juice contains citric acid, making it acidic in nature.

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Section 2: True/False Questions

#### i. Nitric acid turns red litmus blue. False
- Explanation: Nitric acid is an acid. Acids turn blue litmus red, not red litmus blue. Therefore, this statement is false.

#### ii. Sodium hydroxide turns blue litmus red. False
- Explanation: Sodium hydroxide (NaOH) is a base. Bases turn red litmus blue and blue litmus red. Therefore, sodium hydroxide would turn blue litmus red, but the statement incorrectly says "blue litmus red," so it is false.

#### iii. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. True
- Explanation: Sodium hydroxide (NaOH) is a base, and hydrochloric acid (HCl) is an acid. When they react, they undergo a neutralization reaction:
\[
\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}
\]
Here, NaCl (sodium chloride) is the salt, and H₂O is water. This statement is true.

#### iv. Indicator is a substance which shows different colours in acidic and basic solutions. True
- Explanation: An indicator is a substance that changes color in the presence of acids or bases. For example, litmus paper turns red in acidic solutions and blue in basic solutions. This statement is true.

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Final Answers:

#### Section 1: Fill in the Blanks
i. indicator
ii. red
iii. blue
iv. mauve (purple)
v. salt
vi. acidic

#### Section 2: True/False
i. False
ii. False
iii. True
iv. True

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Boxed Final Answer:

\[
\boxed{
\text{i. indicator, ii. red, iii. blue, iv. mauve (purple), v. salt, vi. acidic; i. False, ii. False, iii. True, iv. True}
}
\]