[Catalist] Possible effect of Saliva when cutting Glass Tubing?

[Michael McGarry]

Greetings Secondary Chemistry Teachers, 

From my present (I could be wrong) science knowledge, I also respectfully question explanation in leon’s recent post to CATALIST. In answering the titration-technique question from Jackie, Leon stated:

"(BTW, this is why when you are cutting glass tube, you spit on it after scoring it. The pH of your saliva (7.8) is alkaline enough to significantly weaken the newly-exposed Si-O bonds (before they reform again), and make the tube crack along the score mark.”

URL 1: http://www.cmscientific.com/info_sheets/how_to_snap_cut_glass_tubing_and_rod.pdf <http://www.cmscientific.com/info_sheets/how_to_snap_cut_glass_tubing_and_rod.pdf> [The PDF states that the wetting with ‘saliva' of the score-line in the glass tubing is optional.]

Would a ‘possible' chemical reaction of (about neutral) saliva with the Si - O bonds along the scored-line in the glass have sufficient time to weaken the very strong covalent bonds between the Si and O atoms at the exposed glass-surface along the scored-line?

Does mechanical scoring of the surface of the glass tubing (with a triangular file) introduce new mechanical stress into the smooth rounded glass surface like when we always tightly-crimp a sheet of paper in order to neatly tear the paper along the crimped-line?


Possible Contextual Question for our Chemistry students: When we blow our nose into a paper tissue, why is it much easier to blown holes in the paper tissue when the tissue has become wet? [HINT: Why is wet tissue paper much weaker than dry tissue paper?]

URL 2: http://antoine.frostburg.edu/chem/senese/101/consumer/faq/what-is-cellulose.shtml <http://antoine.frostburg.edu/chem/senese/101/consumer/faq/what-is-cellulose.shtml>

URL 3: http://chemwiki.ucdavis.edu/Textbook_Maps/General_Chemistry_Textbook_Maps/Map%3A_Chem1_(Lower)/07%3A_Solids_and_Liquids/7.03%3A_Hydrogen-Bonding_and_Water <http://chemwiki.ucdavis.edu/Textbook_Maps/General_Chemistry_Textbook_Maps/Map:_Chem1_(Lower)/07:_Solids_and_Liquids/7.03:_Hydrogen-Bonding_and_Water>

Best Wishes,

Mike McGarry    


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