The main objective of this lab is to gain experience at a typical synthesis and semi-microscale recrystallization.
1) How fast should the temperature be raised when determining a melting point? When can the temperature be raised more quickly? 2) If there is an Impurity present in a sample, what is the effect on the melting point? 3) Explain why a) salt, spread on roads in the winter, helps prevent icing in, for instance, southern Ontario, and b) salt is useless on the much colder roads of Manitoba. 1) You would have to slowly raise the temperature up when determining the melting point due to the sensitivity of the dulcin being able to change from solid to liquid at any point. If the temperature is set to high to fast it is possible to miss the change of state and not be able to record the time which is why it should originally be set pretty slow. If set high too fast it will melt faster causing the melting point to be inaccurate. As soon as you get the general idea of when change in state will occur, that is when you can probably raise the temperature more quickly.
2) If there are impurities present in the sample it can cause many problems, it can lower or raise the boiling point due to it having an effect on the dulcin itself. Basically it will increase the range of the boiling and melting points, which will give an inaccurate reading. If the dulcin were to be fully pure the range would have a difference of maybe 1 to 2, having an impurity would make a huge difference.
3) Salt is sprinkled on the streets so that when it mixes with the moisture and the water it creates a saline mixture. This mixture has a lower freezing point then normal water does so that means it would only freeze at lower temperatures. This basically prolongs the icing process and basically can fully prevent ice from forming on the roads. On older colder roads of Manitoba it reaches the colder temperatures necessary...