chemistry : class11 Normal Melting Point : Melting point : States of Matter: Gases and Liquids MCQ Questions and Answers
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Normal Melting Point
MCQ questions and answers.
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MCQ Questions
1. What is meant by the normal melting point of a substance?
A.
The temperature at which it boils at 1 atm pressure
B.
The temperature at which its solid and liquid phases are in equilibrium at 1 atm pressure
C.
The temperature at which it changes directly from solid to gas at 1 atm pressure
D.
The temperature at which it freezes at zero pressure
Correct Answer:
The temperature at which its solid and liquid phases are in equilibrium at 1 atm pressure
Explanation:
The normal melting point is the temperature at which a substance changes from solid to liquid, with both phases in equilibrium, under a pressure of 1 atm.
2. At what pressure is the normal melting point measured?
A.
0 atm
B.
0.5 atm
C.
1 atm
D.
10 atm
Correct Answer:
1 atm
Explanation:
The word normal in normal melting point indicates that the melting temperature is measured at standard atmospheric pressure, approximately 1 atm.
3. During melting at the normal melting point of a pure substance, what happens to its temperature while both solid and liquid are present?
A.
It remains constant
B.
It continuously decreases
C.
It continuously increases
D.
It becomes zero
Correct Answer:
It remains constant
Explanation:
At the normal melting point, supplied heat is used for the change of state, so the temperature remains constant until the solid has completely melted.
4. Which phase change occurs at the normal melting point?
A.
Liquid to gas
B.
Gas to liquid
C.
Solid to liquid
D.
Gas to solid
Correct Answer:
Solid to liquid
Explanation:
The normal melting point is the temperature at which a solid changes into a liquid at 1 atm pressure.
5. The normal melting point of ice is approximately:
A.
0 °C
B.
25 °C
C.
50 °C
D.
100 °C
Correct Answer:
0 °C
Explanation:
Ice melts at approximately 0 °C under 1 atm pressure, so 0 °C is its normal melting point.
6. At the normal melting point, which two phases of a pure substance coexist in equilibrium?
A.
Solid and liquid
B.
Liquid and gas
C.
Solid and gas
D.
Only the gas phase
Correct Answer:
Solid and liquid
Explanation:
By definition, the normal melting point is the temperature at which the solid and liquid phases coexist in equilibrium at 1 atm pressure.
7. If a substance has a normal melting point of 80 °C, at what temperature will it melt under 1 atm pressure?
A.
0 °C
B.
40 °C
C.
80 °C
D.
160 °C
Correct Answer:
80 °C
Explanation:
The numerical value of the normal melting point is the melting temperature measured at 1 atm pressure. Therefore, the substance melts at 80 °C.
8. Which instrument is commonly used to measure the temperature of a substance at its normal melting point?
A.
Thermometer
B.
Barometer
C.
Hygrometer
D.
Calorimeter only
Correct Answer:
Thermometer
Explanation:
A thermometer measures the temperature at which the solid and liquid phases are in equilibrium, allowing the normal melting point to be determined.
9. A pure solid begins to melt at 1 atm pressure at 120 °C. What is its normal melting point?
A.
60 °C
B.
100 °C
C.
120 °C
D.
240 °C
Correct Answer:
120 °C
Explanation:
Since the solid begins to melt at 120 °C under 1 atm pressure, its normal melting point is 120 °C.
10. Which statement about the normal melting point is correct?
A.
It is always higher than the normal boiling point
B.
It is measured when a solid changes into a liquid at 1 atm pressure
C.
It is the temperature at which a gas changes into a solid at 1 atm pressure
D.
It is independent of the substance being studied
Correct Answer:
It is measured when a solid changes into a liquid at 1 atm pressure
Explanation:
The normal melting point is substance-specific and is defined as the temperature of solid-to-liquid change at 1 atm pressure.
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