QUESTION: A sample of matter is heated and found to start melting at 75.0oC. While melting, the sample temperature continues to rise to about 85.0oC. This matter is most likely… A. an element, B. a compound, C. a mixture A sharp melting point and a sharp boiling point are characteristics of pure substances (one element or one compound). “Sharp melting point” means temperature remains constant while sample is melting. In practice, a “constant” temperature means “within about 1 degree.” SCRIPT: A sample of matter is heated and found to start melting at 75.0oC. While melting, the sample temperature continues to rise to about 85.0oC. This matter is most likely… A. an element, B. a compound, C. a mixture PAUSE CLICK A sharp melting point and a sharp boiling point is characteristic of pure substances (one element or one compound). When we say that a sample has a “Sharp melting point,” we mean that the sample’s temperature remains constant while it’s melting. In practice, a “constant” temperature means “within about 1 degree.” In this question, we are given a sample that melts over a ten-degree range --- from 75 to 85 degrees Celsius. This is a very strong indication that the sample is not that of a pure substance. Therefore, the correct answer is C. The sample is most likely a mixture. PAUSE CLICK END RECORDING

Video ID: 1-4-3 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08