on 8/8/04 6:29 AM, Guag Meister at [EMAIL PROTECTED] wrote: > Hi all list members ; > > While we are on the subject of pH, can anyone give me > a reasonable explanation as to why the pH of pure > water is 7.0?? And I don't mean because it is in the > middle of the range. >
pH is the negative logarithm of hydrogen ion concentration. Pure water exists mostly as H2O, but a very small amount of it (approx. one part in 10 million) dissociates into a hydroxide ion OH- and a hydrogen ion H+. If you multiply the H+ concentration and the OH- concentration in an aqueous solution, the product is a constant, called the "dissociation constant", which for water has a value of about 10 ^ -14. So pure water has an OH- conc. of 10 ^ -7 and also an H+ conc. of 10 ^ -7. Since the negative log of 10 ^ -7 is 7, it's called pH7. OK so far? Here's the interesting part -- if you add H+ (acid) to an aqueous solution, it will combine with OH- (making water) as required to keep the product of OH- and H+ concentrations at a constant 10 ^ -14. At pH6, for example, H+ is 10 ^ -6 and OH- is 10 ^ -8. Similarly, adding OH- (base) will cause some of the H+ to be scarfed up. At pH9, the OH- concentration is 10 ^ -5 (100X its value in pure water), driving the H+ concentration down to 10 ^ -9. -K ------------------------ Yahoo! Groups Sponsor --------------------~--> Yahoo! Domains - Claim yours for only $14.70 http://us.click.yahoo.com/Z1wmxD/DREIAA/yQLSAA/FGYolB/TM --------------------------------------------------------------------~-> Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Biofuels list archives: http://infoarchive.net/sgroup/biofuel/ Please do NOT send Unsubscribe messages to the list address. To unsubscribe, send an email to: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/biofuel/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
