[gingi]

I have few question concerning two experiment I've done. I've been thinking about the answers, researching the web but I could not figure out the answers

* see in <> my assumptions !!

1) A sample of naphthalene, which should be pure white, was found to have a grayish color after the usual purification procedure. The melting point was correct and the melting range small. Explain the gray color.

<I assume it's not pure - however - howcome its melting point remains the same ? The impurity affects the range ?>

2)Under which circumstances is it wise to use a mixture of solvents to carry out a crystallization ?

<again, I assume - by reasoning - that once we have 2 liquids with the same solvent - properties, it won't matter if their mixture will be used as one solvent>

3) If a little activated charcoal does a good job removing impurities in a crystallization, why not use a large quantity ?

<the only thing I can think of is that the mass of the charocal will influence the results>

[AWK]

1. Usuall purification procedure for naphtalene is sublimation - always crystals are white

2. It is quite complex problem - it depends on the method of crystallization
(evaporation of one solvent, change of temperatute and so on)

3. Excess of charcoal decreases yield.

[gingi]

Hi and thanks for answering !

          1. Usuall purification procedure for naphtalene is sublimation - always crystals are white
         
           So I might be the reason for the grayish color ? I mean, the question is from crystalization - so I don't  
           understnad. Even in sublimation - what can make it gray ?

2. It is quite complex problem - it depends on the method of crystallization
(evaporation of one solvent, change of temperatute and so on)

3. Excess of charcoal decreases yield.
Thanks.

[Dude]

The return question would be:

Did you use charcoal in your work-up?  If so, the gray color is probably from residual charcoal.  Filtration through Celite or clay-type materials helps keep out decolorants and might help avoid sublimation.

[Borek]

A sample of naphthalene, which should be pure white, was found to have a grayish color after the usual purification procedure. The melting point was correct and the melting range small. Explain the gray color.

<I assume it's not pure - however - howcome its melting point remains the same ? The impurity affects the range ?>

Charcoal forms a suspension, not a solution.

[gingi]

No. I didn't use it. This is a question taken straight from the text  - I assumed it's the charocal as well - but what I don't understant is how impurity relates to color. I've been trying to ace it online - but couldn't find anything.