Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of . The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
Answer the following questions:
(a) Solution P is a strong acid while solution Q is a strong base. On the pH scale, where would you place the solutions P and Q? [1]
(b) A solution has a pH of 7. Name a compound you would use to (i) increase its pH, and (ii) decrease its pH. [1]
(c) (i) When the pH of a solution is decreased from 4 to 2, what effect does it produce on its hydronium ion concentration? State the colour change shown by the pH paper. [2]
OR
(c) (ii) A person is feeling pain and irritation in the stomach due to indigestion. What could be the pH of the fluid in the stomach? Write the common name of the medicines people use for remedy. Give the chemical name of "milk of magnesia" often used for this purpose. [2]
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of . The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
Answer the following questions:
(a) Solution P is a strong acid while solution Q is a strong base. On the pH scale, where would you place the solutions P and Q? [1]
(b) A solution has a pH of 7. Name a compound you would use to (i) increase its pH, and (ii) decrease its pH. [1]
(c) (i) When the pH of a solution is decreased from 4 to 2, what effect does it produce on its hydronium ion concentration? State the colour change shown by the pH paper. [2]
OR
(c) (ii) A person is feeling pain and irritation in the stomach due to indigestion. What could be the pH of the fluid in the stomach? Write the common name of the medicines people use for remedy. Give the chemical name of "milk of magnesia" often used for this purpose. [2]
a) 0, 14; b) i) NaOH, ii) HCl; c) i) increases, red to yellow; c) ii) 1.5-2.5, antacids, magnesium hydroxide
Marking Scheme
- 1a) 0, 14
- 2b) i) NaOH
- 3b) ii) HCl
- 4c) i) increases, red to yellow
- 5c) ii) 1.5-2.5, antacids, magnesium hydroxide
Hint
Use the pH scale to determine the acidity or basicity of a solution. Remember that a pH of 7 is neutral, while a pH less than 7 is acidic and a pH greater than 7 is basic. Use the pH paper to determine the color change as the pH decreases from 4 to 2.
Quick Oral Answer
The pH scale is used to measure the acidity or basicity of a solution. A pH of 7 is neutral, while a pH less than 7 is acidic and a pH greater than 7 is basic. The pH of a solution can be increased by adding a base, and decreased by adding an acid. The hydronium ion concentration increases as the pH decreases. The pH paper shows a color change from green to red as the pH decreases from 4 to 2. Antacids are commonly used to remedy indigestion, and milk of magnesia is a common antacid that contains magnesium hydroxide.
Analysis & Explanation
The pH scale is used to measure the acidity or basicity of a solution. A pH of 7 is neutral, while a pH less than 7 is acidic and a pH greater than 7 is basic. The pH of a solution can be increased by adding a base, and decreased by adding an acid. The hydronium ion concentration increases as the pH decreases. The pH paper shows a color change from green to red as the pH decreases from 4 to 2. Antacids are commonly used to remedy indigestion, and milk of magnesia is a common antacid that contains magnesium hydroxide.
Common Mistakes
- 1confusing the pH scale with the acidity or basicity of a solution
- 2not remembering that a pH of 7 is neutral
- 3not knowing how to use the pH paper to determine the color change as the pH decreases from 4 to 2
Interesting Facts
The pH scale was developed by Soren Sorensen in 1909.
The pH scale is used to measure the acidity or basicity of a solution.
A pH of 7 is neutral, while a pH less than 7 is acidic and a pH greater than 7 is basic.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2025?
This question carries 4 marks in the CBSE Class 10 Science 2025 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Acids, Bases and Salts" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Acids, Bases and Salts" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2025 paper?
This question appears in Section E in the CBSE Class 10 Science 2025 paper.