MadSci Network: Chemistry

Re: Silicon Dioxide is present in a candy named 'Chewy Sweet Tarts'

Date: Mon Apr 27 16:31:12 1998
Posted By: Ken Johnsen, MadSci Admin
Area of science: Chemistry
ID: 893692273.Ch

Hi Carolyn!

I bet if the label said it contained 'sand' that you'd be writing to the 
manufacturer and not to The MAD Scientist!

Silicon dioxide [SiO2] and silicate minerals make up 95% of the Earth's crust 
and the natural forms consist of crystalline, microcrystalline and diatomaceous 
[from diatoms, the skeleton of tiny marine creatures]. The crystalline sand on 
a beach has an average particle size of from 2 to about 10 microns. This grain 
size is visible to the naked eye and, if you ever got some in your eye, could 
be felt as well by the eye. 

Synthetic SiO2 is exactly the same compound but is a microscopic particle with 
sizes as low as 0.007 microns, or 1000 times smaller than beach sand. This 
material is not found in nature but is synthesized in a chemical reactor. The 
chemistry is straightforward:

Silicon tetrachloride [SiCl4, made from SiO2 and HCl] is hydrolyzed in a flame 
of oxygen and hydrogen [the same fuel that is burned to launch the space 
shuttle]. Thus:

2 H2 + O2 + SiCl4  -->  SiO2 + 4HCl

Why bother to take perfectly good ordinary sand and go through all these 
gyrations just to make more sand?

The answer is in the very small particle sizes that can be obtained with this 
process. As particle size decreases, surface area increases. As surface area 
increases more and more water can be sorbed via hydrogen bonding and aggregates 
of particles begin to form with a structure similar to a bunch of grapes.

If this form of SiO2 is added to a candy [or practically any other food] it 
sets up a jelly-like structure of associated agglomerates that gives a texture 
and viscosity unattainable via other means.

SiO2 is inert and non-toxic and is FDA approved for this use. There are also 
many other industrial uses.


Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1998. All rights reserved.