Which method is the most suitable for separating a mixture of sodium chloride and iodine?A) crystallization,B) filtration,C) fractional distillation,D) sublimation?

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ndnordic's profile pic

ndnordic | High School Teacher | (Level 2) Associate Educator

Posted on

Of the choices listed, the best would be sublimation.  Sublimation is a physical process in which a substance changes from a solid directly to a gas without passing through the liquid phase. A common example of this process  is dry ice. When you put a piece of dry ice into a room, you immediately see a cloud forming around the dry ice. What is happening is that the dry ice is very cold and the CO2 gas coming off the piece of solid dry ice is cold enough to cause the moisture in the air to condense, forming the cloud you see.

Mothballs and iodine are two other substances that will sublime.  To separate the salt and iodine, place both in a beaker and place a watch glass or evaporating dish on top of the beaker.  Put some ice in the top of the evaporating dish.  Now gently warm the bottom of the beaker and the iodine will sublime into a gas. As it rises and hits the bottom of the cold evaporating dish it will deposit on the underside of the dish  as iodine crystals.  You can then scrape the iodine crystals off the dish and put them into a container.  The salt, being a crystalline solid, has a very high melting point and will remain in the beaker, unaffected by the gentle heating.

william1941's profile pic

william1941 | College Teacher | (Level 3) Valedictorian

Posted on

 

Iodine on being slightly heated changes directly from solid to gas. These vapors condense into a solid crystalline structure when then they come in contact with a cold surface. Sodium chloride on the other hand has a very high temperature of changing state. It melts at over 800 degrees.

To separate sodium chloride and iodine the best way is to slightly heat the mixture. The dark purple vapors of iodine can be collected and cooled to give solid iodine. During this process the sodium chloride is not affected and hence this is the perfect way of separating the two.

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