A student determines the melting point of a solid, X.
The student:
places a sample of solid X in a boiling tube
melts the solid completely
places the boiling tube in a rack and allows it to cool
records the temperature of X every 30 seconds
The results are shown in Table 1.1.
Table 1.1
time / s | 0 | 30 | 60 | 90 | 120 | 150 | 180 | 210 | 240 | 270 | 300 |
|---|---|---|---|---|---|---|---|---|---|---|---|
temperature / °C | 72.0 | 66.5 | 61 | 56.0 | 53.0 | 53.0 | 53.0 | 53.0 | 50.5 | 46.0 | 41.5 |
Name the piece of apparatus the student uses to measure the temperature of X.
The student melts the solid by standing the boiling tube in a beaker of hot water, rather than by heating the boiling tube directly in a Bunsen burner flame.
Suggest two reasons for melting the solid in this way.
The student records all of the temperatures to the nearest 0.5 °C.
One value in Table 1.1 is not recorded to this degree of precision.
State this value.
State the melting point of X.
Explain how you used the results in Table 1.1 to decide.
The student repeats the experiment using a sample of X that contains an impurity.
Describe two ways in which the results for the impure sample are different.
Suggest one improvement to the student's method that would give a more accurate value for the melting point of X.
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