Engineering Chemistry Multiple Choice Questions on “Melting Point”.
1. The purity of the compound is confirmed by ____________
a) Its melting point and boiling point
b) Chromatographic technique
c) Spectroscopy
d) All of the mentioned
Answer: d
Clarification: The purity of the compound is confirmed by its melting point and boiling point, chromatographic technique and spectroscopy.
2. Select the correct statement from the following options.
a) The transformation of solid to liquid is called melting and the reverse process is called freezing
b) The transformation of solid to liquid is called freezing and the reverse process is called melting
c) The transformation of liquid to solid is called melting and the reverse process is called freezing
d) None of the mentioned
Answer: a
Clarification: The transformation of solid to liquid is called melting and the reverse process is called freezing.
3. The temperature at which solid and liquid coexist in equilibrium is called ____________
a) Melting point of liquid
b) Freezing point of liquid
c) Freezing point of solid
d) All of the mentioned
Answer: b
Clarification: The temperature at which solid and liquid coexist in equilibrium is called melting point of solid or freezing point of liquid.
4. Select the incorrect statement from the following option.
a) Every pure solid crystalline substance has a characteristic and unique melting point
b) Impure sample of substance has different melting point
c) Two different pure substances have same melting points
d) Melting point serves as the criteria of purity of a solid substance
Answer: c
Clarification: Two different pure substances have different melting points. All the other options are correct. Every pure solid crystalline substance has a characteristic and unique melting point and impure sample of substance has different melting point. Melting point serves as the criteria of purity of a solid substance.
5. When the solid and liquid phase are in equilibrium, the temperature ____________
a) Increases gradually
b) Decreases gradually
c) Remains constant
d) None of the mentioned
Answer: c
Clarification: When the solid and liquid phase are in equilibrium, the temperature remains constant. The heat is absorbed in changing from one state to another, so no temperature change occurs.
6. The melting point of ice is ____________
a) 00C
b) 1000C
c) 40C
d) -40C
Answer: a
Clarification: The melting point of ice at 1 atmosphere of pressure is very close to 0 °C (32 °F, 273.15 K); this is also known as the ice point. In the presence of nucleating substances the freezing point of water is the same as the melting point, but in the absence of nucleators water can supercool to −42 °C (−43.6 °F, 231 K) before freezing.
7. Molar heat of fusion is defined as ____________
a) Energy required to melt one gram of solid
b) Energy required to melt one mole of solid
c) Energy required to melt one kilogram of solid
d) Energy required to melt ten moles of solid
Answer: b
Clarification: Molar heat of fusion is defined as the energy required to melt one mole of solid at a given temperature. The molar heat of fusion refers to the enthalpy change per amount of substance in moles.
8. The temperature remains constant during phase change because the increased kinetic energy is used to overcome the cohesive forces in the liquid.
a) True
b) False
Answer: a
Clarification: The temperature remains constant during phase change because the increased kinetic energy is used to overcome the cohesive forces in the liquid. The heat is absorbed in changing from one state to another, so no temperature change occurs.
9. What is the molar heat of fusion (kJ/mol) of water?
a) 1.3
b) 0.84
c) 7.61
d) 6.01
Answer: d
Clarification: The molar heat of fusion of water is 6.01 kJ/mol. The molar heat of fusion refers to the enthalpy change per amount of substance in moles.
10. What is the melting point of mercury?
a) 3570C
b) -390C
c) 00C
d) 1000C
Answer: b
Clarification: The melting point and freezing point of mercury is 234.32 kelvins (−38.83 °C or −37.89 °F).