MadSci Network: Earth Sciences

Re: Would ph in rain differ enough from tap water to base a project on it?

Date: Tue Sep 25 11:31:06 2001
Posted By: Alex Barron, Graduate Student, Ecology(Biogeochemistry)
Area of science: Earth Sciences
ID: 1000489283.Es

	The only way to be certain is to check!  But, yes, the pH values 
are probably quite different.  The pH of rain in our part of the world 
tends to be quite low, around 4.3-4.4 (too see a map of pH for 
the US check out:  
href=" ) 
 I can't vouch for your tap water but the water out of our tap is about pH 
7.5.  Because pH is a log scale, every pH unit means a 10-fold change in H+ 
concentration.  So, there is 1000 times less H+ ion in the tap water in our 
lab compared to the rain - a pretty big difference.   
	There are lots of things to think about here.  You might want to 
learn about why pH of rain differs over the US (as you see in the map).  
The pH of deposition can also vary over changes in elevation and based 
upon how much it has rained recently.  Your tap water might also have a 
very different pH depending upon where the water comes from (a hint here: 
the type of bedrock makes a big difference).  You could also examine the pH 
of bottled water - many brands will tell you where the water came from.


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