When salt is spread on snow covered roads at -2 deg C, the snow melts. When the same amount of salt is spread on snow covered roads at -30 deg C, nothing happens. Explain.
I think this is a poor question because it doesn't differentiate between the "same" amount and what might be considered a "normal" amount. At any rate, a minimum amount of salt lowers the freezing point of the -2 degrees snow to a temperature less than -2; therefore, it melts. When the same amount is placed on the -30 degrees snow, it lowers the melting point to say -3 or so but not below -30; therefore, it doesn't melt.
