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Name: Miguel
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 10/2/2004


Question:
Can boiling chips contaminate a mixture or substance when distilling? If so, what should a student do?


Replies:
Hi Miguel

With a normal and correct use there is not such a chance. Boiling chips are made of glass or porcelain small pieces. They are stable at temperature where distillation occurs, so will not contaminate the distilling substances and stay on the distilling flask. Of course one must use appropriate boiling chips not breakable glass. If the glass used is weak it can be broken and then could maybe spoil your experience. But even then the glass will not distillate at all so you will have your condensate pure and separate as expected.

Thanks for asking NEWTON!

Mabel
(Dr. Mabel Rodrigues)


Boiling chips are usually made of silicates that are inert to most chemical reactions and under the conditions of distillation. Even if the chips break apart into tiny fragments, the chances of the small fragment being entrained (distilled over and combined with the distillate) is very small if the distillation is done correctly.

Greg (Roberto Gregorius)


Hi Miguel

With a normal and correct use there is not such a chance. Boiling chips are made of glass or porcelain small pieces. They are stable at temperature where distillation occurs, so will not contaminate the distilling substances and stay on the distilling flask. Of course one must use appropriate boiling chips not breakable glass. If the glass used is weak it can be broken and then could maybe spoil your experience. But even then the glass will not distillate at all so you will have your condensate pure and separate as expected.

Thanks for asking NEWTON!

Mabel
(Dr. Mabel Rodrigues)


It is true, boiling chips are chosen to be substances which do not dissolve in or contaminate most chemicals. But every solid is strongly vulnerable to some liquid chemical, and faintly vulnerable to many. Boiling chips are an old, practical invention rather than an impervious ideal tool, so it is smart to understand why your boiling-chip substance is OK for your application.

If you are really trying to stay pure, there are at least 4 kinds of substances that boiling chips are made of: glass, ceramics of various oxides (aluminum oxide included most often), pure carbon in a glassy form, and porous white virgin DuPont's Teflon (TM). You get to think through what the possible bad effects might be.

Glass and ceramics are always soluble in water to some really low concentration, enough that the glass would be pitted and foggy and the ceramic would crumble after years in steadily boiling water. Possibly this is not a problem for your purification. On the other hand, DuPont's Teflon (TM) chips might be mostly unchanged in all that time.

If your mixture contains organic substances which slowly degrade at the distillation temperature, one kind of stone might catalyze the degradation more than others. You would have to find out for yourself. Such degradations include partial oxidizing (turning dark), polymerizing (making sludge), and fragmenting (making smaller molecules which can vaporize).

Using brand new chips out of the jar makes sure that they have not surface-adsorbed some substance when someone else used them. You also might consider boiling them in 1 or 2 solvents you consider "clean", and then drying them out, before you introduce them to your samples.

Most times in high school, none of this matters. If you do chemistry experiments Junior year in college, it will be expected that you at least think of these things in passing, just to verify that you are not doing something gratuitously dumb, like putting glass chips in HF or NaOH solutions, which eat glass. Most times, boiling chips do not need much thinking.

Jim Swenson



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