posted by Sammy .
When salt is spread on a snow-covered road at -2C, the snow melts. Though when the same amount of salt is spread on the snow covered road at -30C, nothing happens. Explain?
Is this diue to beinf ionic, and nonvolatile vapor and volatile vapor pressure?
Personally I think the question is too vague; therefore, I don't think it is a good question. Why does the first application at -2 degrees C melt? It is because the NaCl lowers the melting point of ice to below -2 so it melts. The second application with snow at -30 C will melt, too, if enough NaCl is added. The question might make more sense if the first application at -2 said that just enough NaCl was added to melt it, then that SAME amount of NaCl would not melt snow at -30.
DrBob222 is perfectly correct although it does say in the question that the same amount of salt is added at both temperatures. when the snow is at -2 degrees the addition of the NaCl lowers the temperature that the snow melts at to somewhere between -2 and -30 degrees. However the same amount of NaCl being added to the snow at -30 degrees does not lower the melting point below -30 degrees, which of course means that the snow will not melt.