Consider three liquids: Hydrochloric acid,… - NCERT Class 7 Science MCQ

NCERT Class 7 Science — Chapter 1: Acids, bases and salts

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Consider three liquids: Hydrochloric acid, Sodium hydroxide, and Sugar solution. If tested with a turmeric indicator, which one of the following observations is correct?

NCERT textbook question

From NCERT Science - class 7 · Page 41

Options

AHydrochloric acid turns the indicator red.
BAll three liquids turn the indicator red with varying intensity.
CSodium hydroxide turns the indicator red.
DSugar solution turns the indicator green.

Did you get this right?

Solution

Correct Option

The correct option is

Sodium hydroxide turns the indicator red.

Explanation

Turmeric is a natural acid-base indicator derived from the Curcuma longa plant. Its active component, curcumin, exhibits specific color changes based on the pH of the medium. It is primarily used to identify basic (alkaline) substances.

Analysis of Liquids

Hydrochloric Acid (Acidic): Turmeric indicator remains yellow in acidic environments. It does not turn red.
Sodium Hydroxide (Basic): Turmeric indicator changes color from yellow to deep red (or reddish-brown) in the presence of bases. This confirms the basic nature of Sodium Hydroxide.
Sugar Solution (Neutral): Turmeric indicator remains yellow in neutral solutions. It shows no color change.

Based on these properties, only Sodium Hydroxide turns the indicator red.

Key Takeaway: Turmeric is a natural indicator that turns red in basic solutions but remains yellow in both acidic and neutral solutions.

Your note

More from Chapter 1: Acids, bases and salts

With reference to the chemical nature of substances, consider the following statements: 1. All substances that taste sour contain acids. 2. Substances that taste bitter and feel soapy on touching are generally acidic in nature. 3. Baking soda is an example of a substance that has a bitter taste and is basic in chemical nature. Which of the statements given above is/are correct?

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Consider the following statements: 1. All acids are bitter to taste. 2. Bases that are soluble in water are called alkalis. 3. Indicators are substances that change colour in acidic and basic solutions. Which of the statements given above is/are correct?

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Consider the following statements regarding the preparation of indicators: 1. Litmus is obtained from a plant called Pitcher plant. 2. Turmeric paper is made by depositing turmeric paste on blotting paper. 3. China rose indicator is prepared by keeping petals in warm water. Which of the statements given above is/are correct?

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Which one of the following acids is primarily responsible for the sour taste of unripe mangoes?

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With reference to the use of Calamine solution, consider the following statements: 1. It is used to treat skin irritation caused by ant bites. 2. It contains Calcium carbonate. 3. It is applied on the skin to neutralize the effect of wasp stings. Which of the statements given above is/are correct?

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Keep practising Chapter 1: Acids, bases and salts

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