1. Which apparatus is commonly used to determine the melting point of a small solid sample?
A.
Thiele tube
B.
Gas jar
C.
Separating funnel
D.
Volumetric flask
Correct Answer:
Thiele tube
Explanation:
A Thiele tube is commonly used for melting point determination because it provides uniform heating of the sample in a capillary tube.
2. In the capillary method, where is the solid sample placed for melting point determination?
A.
Inside a thin capillary tube
B.
Inside a gas jar
C.
On a watch glass only
D.
Inside a burette
Correct Answer:
Inside a thin capillary tube
Explanation:
A small amount of powdered solid is packed into a thin capillary tube for observing its melting behavior.
3. The sample in a melting point capillary should be packed at which position?
A.
Near the closed end
B.
At the open top only
C.
At the middle of the thermometer bulb
D.
At the bottom of the heating bath
Correct Answer:
Near the closed end
Explanation:
The solid sample is packed near the closed end of the capillary so that it can be heated and observed properly.
4. Which instrument is used to measure the temperature during melting point determination?
A.
Thermometer
B.
Measuring cylinder
C.
Pipette
D.
Balance
Correct Answer:
Thermometer
Explanation:
A thermometer measures the temperature at which the solid begins to melt and becomes completely liquid.
5. Why is the solid sample usually powdered before placing it in the capillary tube?
A.
To ensure uniform heating
B.
To increase its color
C.
To make it dissolve in water
D.
To lower the thermometer reading
Correct Answer:
To ensure uniform heating
Explanation:
Powdering and compacting the sample helps it heat uniformly, giving a more reliable melting point.
6. During melting point determination, the sample should generally be heated how?
A.
Slowly near the expected melting point
B.
As rapidly as possible throughout
C.
Without any heat
D.
Only after cooling it below room temperature
Correct Answer:
Slowly near the expected melting point
Explanation:
Slow heating near the expected melting point allows accurate observation of the temperature range in which melting occurs.
7. What temperature is recorded when the first part of the solid starts to liquefy?
A.
The beginning of the melting range
B.
The boiling point
C.
The freezing point of water
D.
The room temperature
Correct Answer:
The beginning of the melting range
Explanation:
The temperature at which the first liquid appears is recorded as the beginning of the melting range.
8. What temperature is recorded when the solid has completely changed into a liquid?
A.
The end of the melting range
B.
The room temperature
C.
The density point
D.
The sublimation point
Correct Answer:
The end of the melting range
Explanation:
The temperature at which the last solid particle disappears is recorded as the end of the melting range.
9. A pure solid usually shows which type of melting behavior during determination?
A.
A sharp melting point
B.
No melting at any temperature
C.
Only boiling behavior
D.
A very wide melting range
Correct Answer:
A sharp melting point
Explanation:
A pure solid generally melts over a narrow temperature range, often described as a sharp melting point.
10. What does a broad melting range generally suggest about a solid sample?
A.
The sample may contain impurities
B.
The thermometer is unnecessary
C.
The sample is certainly a pure compound
D.
The sample has no definite temperature
Correct Answer:
The sample may contain impurities
Explanation:
Impurities commonly cause a solid to melt over a broader and often lower temperature range than a pure sample.
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