2. Use the melting point phase diagram in the lab manual to help answer this que
ID: 846760 • Letter: 2
Question
2. Use the melting point phase diagram in the lab manual to help answer this question. If you compare the melting point of a slightly impure mixture with the melting point of a pure compound, the melting point of the slightly impure mixture will be: a. broader and lower than the eutectic mixture. b. sharper and lower than the eutectic mixture. c. broader and higher than the eutectic mixture. d. sharper and higher than the eutectic mixture. Explain briefly: 3. For very accurate determination of melting points, scientists use thermometers that have been calibrated by measuring the melting points of known standards. You did not calibrate your thermocouple. What data obtained during this experiment allows you to be confident that the thermometer system you were asking wa not giving readings that were inaccurate by 10 degrees or more?Explanation / Answer
Ans: Broader and higher than the eutectic mixture (c)
When an impurity is added to pure material, there is one unique mixture of two compounds, A and B, that has a lower melting point than any other mixture of the two compounds. This particular mixture is called the eutectic mixture. The melting point of the eutectic mixture is called the eutectic point. A mixture whose composition corresponds exactly to its eutectic mixture will have a relatively sharp melting point..
2nd part answer
If one measures the melting point of the compound with uncorrected thermometer (remember the melting point is known, let it be y) one will obtain a certain melting point x. If x=y no correction has to be done. But if it differs, all melting points of samples with unknown melting points have to be corrected by the factor z (difference between x and y). If x and y are same then there is no need of calibration of thermometer.
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