Boiling Point of Water (Determination) MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz covers Unit I: Practicals, focusing on the determination of the boiling point of water. Topics include the experimental procedure, required apparatus, observations, and safety precautions. Test your knowledge, submit the quiz to see your score, and download the detailed PDF answer key for revision.
Overview: Determination of Boiling Point of Water
The boiling point of water is defined as the temperature at which its vapor pressure becomes equal to the atmospheric pressure. For pure water at standard atmospheric pressure (1 atm), the boiling point is 100 degrees Celsius (373 K). This experiment in Class 9 Science involves heating water in a beaker or boiling tube and recording the temperature at steady intervals until it remains constant.
Key Learning Points
- The Constant Temperature: During boiling, the temperature of water remains constant even though heat is continuously supplied. This constant temperature is the boiling point. The heat energy is used as latent heat of vaporization to change the state from liquid to gas.
- Apparatus Setup: The thermometer bulb should be immersed in water but must not touch the bottom or sides of the container to ensure it measures the water temperature, not the glass temperature.
- Prevention of Bumping: Pieces of porcelain or pumice stone are added to the water before heating to ensure smooth boiling and prevent sudden “bumping” or spurting of water.
Factors Affecting Boiling Point
| Factor | Effect on Boiling Point |
|---|---|
| Impurities (e.g., Salt) | Increases the boiling point (Elevation in boiling point). |
| Atmospheric Pressure | Directly proportional. Higher pressure increases BP; lower pressure (altitude) decreases BP. |
Quick Revision Notes
- Standard Boiling Point: 100 C or 373 K at sea level.
- Thermometer Range: A laboratory thermometer with a range of -10 C to 110 C is typically used.
- Distilled vs. Tap Water: Distilled water boils at exactly 100 C (at 1 atm), while tap water may boil slightly above 100 C due to dissolved salts.
Extra Practice Questions
- Why is a Clinical Thermometer not used for this experiment? (Answer: Its range is too short, usually 35-42 C).
- What happens to the temperature of water once it starts boiling violently? (Answer: It stays constant).
- Convert 105 C to Kelvin scale. (Answer: 378 K).
- Why do we use a wire gauze on the tripod stand? (Answer: To distribute heat evenly to the beaker).
- Does water boil at a lower temperature on a mountain top? (Answer: Yes, because atmospheric pressure is lower).
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