Questions and Answers
What are common acid-base indicators and their primary utility?
Common acid-base indicators include litmus, methyl orange, and phenolphthalein, and they primarily indicate whether a solution is acidic or alkaline.
Explain the main difference between common indicators and universal indicators.
Common indicators indicate whether a solution is acidic or alkaline, whereas universal indicators provide information about the strength or pH range of the solution.
How does the color of litmus indicator change in acidic and alkaline solutions?
Litmus turns red in acidic solutions and blue in alkaline solutions.
What role do indicators play in agriculture?
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In what pH range does methyl orange change color, and what colour indicates a neutral solution?
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Why is the pH of milk significant for dairies?
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What pH value is associated with acetic acid (vinegar) and how does it compare to human blood?
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Describe the color changes of phenolphthalein in different pH environments.
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What pH value indicates a strongly alkaline solution?
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How can universal indicators help in technology and medicine?
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Study Notes
Common Acid-Base Indicators
- Common indicators include Litmus, methyl orange, and phenolphthalein.
- These indicators show whether a solution is acidic or alkaline but do not indicate the strength of the solution.
- They cannot differentiate among solutions with different pH levels, exhibiting abrupt color changes at specific pH levels (e.g., methyl orange changes color between pH 3 and 4).
- Litmus is derived from certain lichens and is prepared by dissolving 0.5g in 1 liter of distilled water.
Universal Indicators
- Universal indicators consist of mixed organic dyes, such as pH paper or solutions.
- They provide a pH range and indicate the strength of acidic or alkaline solutions.
- These indicators can distinguish between various acidic and alkaline solutions, showing different colors at different pH levels (e.g., transitions from blue to indigo to violet between pH 7 and 14).
Colour Changes by Indicators
- Litmus: Purple (neutral), Red (acidic), Blue (alkaline).
- Methyl orange: Orange (neutral), Pink (acidic), Yellow (alkaline).
- Phenolphthalein: Colourless (neutral & acidic), Pink (alkaline).
Utility of Indicators in Various Fields
- Agriculture: Soil pH is tested to optimize crop growth; different crops require specific pH levels (e.g., citrus fruits prefer slightly alkaline soil).
- Dairies: A pH change in milk (normal pH 6.6) signifies spoilage.
- Technology: Controlled pH is crucial for biochemical and organic reactions.
- Medicine: Blood and urine pH values are vital for diagnosing diseases.
pH Values of Common Substances
-
Acidic Solutions:
- Dilute hydrochloric acid (0.1N): pH 1.0
- Dilute sulfuric acid (0.1N): pH 1.2
- Acetic acid (vinegar): pH 2.9
- Tartaric acid (grapes): pH 3.5
- Lactic acid (milk): pH 6.6
-
Alkaline Solutions:
- Human blood: pH 7.3
- Albumin (egg): pH 7.9
- Sea water: pH 8.5
- Ammonium hydroxide (0.1N): pH 11.1
- Sodium hydroxide (0.1N): pH 13.0
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Description
Test your knowledge on common acid-base indicators such as litmus, methyl orange, and phenolphthalein. This quiz explores their utility, limitations, and color-change characteristics at different pH levels. Discover how these indicators help identify acidic and alkaline solutions.
