NCERT Solutions for Class 7 Science Chapter 5
Important NCERT Questions
7th Chapter 5 Acids, Bases and Salts
NCERT Books for Session 2022-2023
CBSE Board and State Board
Questions No: 9
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
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Turmeric is yellow in colour. When a base is added to it, the solution turns into pink colour. However turmeric remains yellow when an acid or neutral solution is added to it. We shall perform the following steps to identify the solution is base, acid or neutral.
• Take few drops from each solution and test it with turmeric solution. If the solution turns into pink colour that solution is base i.e. Sodium Hydroxide. Mark that beaker (containing solution) as base.
• Take a test tube and add few drops of base solution and second solution. Check if test tube becomes warm and then add turmeric solution to it. If the colour does not change, it means the solution added is acidic (HCl). The test tube becomes warm due to neutralization.
• If the test tube of the above solution does not warm and it does show pink colour when turmeric is added, the second solution is neutral.
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Using turmeric indicator, you can distinguish between hydrochloric acid, sodium hydroxide, and a sugar solution based on their reactions:
1. Hydrochloric Acid (HCl):
– Adding turmeric indicator to a portion of the unknown liquid will result in a color change. Hydrochloric acid, being acidic, turns turmeric indicator from yellow to reddish-orange or pinkish due to its acidic properties.
2. Sodium Hydroxide (NaOH):
– Introducing turmeric indicator to another portion of the liquid will show a different color change. Sodium hydroxide, a strong base, alters the turmeric indicator from yellow to brown or dark reddish-brown due to its alkaline nature.
3. Sugar Solution:
– Applying turmeric indicator to the third portion of the liquid might show minimal to no change in color. A sugar solution, being neutral, is unlikely to significantly affect the turmeric indicator, maintaining the yellow color.
By observing the color changes in the turmeric indicator when added to each liquid, it’s possible to identify hydrochloric acid by a reddish-orange or pinkish color, sodium hydroxide by a brown or dark reddish-brown color, and the sugar solution by minimal or no change (maintaining yellow). This method helps differentiate the acidic, basic, and neutral properties of the given liquids.