The image you've provided is an
answer key for a worksheet titled *"Acids, Bases, and the pH Scale"*. It includes two questions with their correct answers already filled in. Let's go through each question and explain the solution in detail.
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Q.1: Fill in the blanks with suitable words.
a) The _pH scale_ measures how acidic or basic a substance is.
✔ Explanation: The pH scale is a logarithmic scale used to specify the acidity or basicity of a solution. It quantifies the concentration of hydrogen ions (H⁺) in a solution.
b) pH scale ranges from _0_ to _14_.
✔ Explanation: The standard pH scale goes from 0 to 14. This range covers all possible acidities and basicities of aqueous solutions at room temperature.
c) A solution has a pH of 7, it's _neutral_.
✔ Explanation: A pH of 7 indicates neutrality — this is the pH of pure water at 25°C. At this point, the concentrations of H⁺ and OH⁻ ions are equal.
d) A pH less than 7 is an _acid_, with _lower_ numbers indicating stronger acids.
✔ Explanation: Solutions with pH < 7 are acidic. The lower the number (closer to 0), the higher the concentration of H⁺ ions, meaning the stronger the acid. For example, lemon juice (pH ~2) is more acidic than vinegar (pH ~3).
e) A pH greater than 7 is a _base_, with _higher_ numbers indicating stronger bases.
✔ Explanation: Solutions with pH > 7 are basic (or alkaline). Higher values (closer to 14) indicate stronger bases. For example, baking soda (pH ~9) is less basic than household ammonia (pH ~11).
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Q.2: Fill the blanks with following words to identify ranges of the pH scale.
Words given:
- neutral
- acidic
- basic
The diagram shows the pH scale from 0 to 14 with color gradation:
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Red to yellow-green (0–6): Labeled as
acidic
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Green (7): Labeled as
neutral
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Blue to purple (8–14): Labeled as
basic
✔ Explanation:
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Acidic (0–6): These solutions have more H⁺ ions than pure water.
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Neutral (7): Equal H⁺ and OH⁻ ions; balanced.
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Basic (8–14): These solutions have more OH⁻ ions than pure water.
This classification helps in understanding the nature of substances based on their pH.
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✔ Summary of Key Concepts:
| pH Range | Nature | Examples |
|---------|-------------|----------------------------------|
| 0 – 6 | Acidic | Lemon juice, vinegar, battery acid |
| 7 | Neutral | Pure water, saliva |
| 8 – 14 | Basic | Baking soda, soap, bleach |
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Final Note:
This worksheet is designed to teach students how to interpret the pH scale and classify substances as acidic, neutral, or basic. The answer key confirms that the student correctly understands these fundamental chemistry concepts.
Let me know if you'd like a version of this worksheet without answers for practice!
Parent Tip: Review the logic above to help your child master the concept of acids bases worksheet.
