m777182 - you are wrong. While HNO3 is strong (although much weaker than HCl and first step of H2SO4) HNO2 is simply weak acid, with pKa 3.37.
General Chemistry Software
www.pH-meter.info
These 'devices' are IMHO not worth even these 10 bucks. If it is for gardening, pH stripes with pH range 5-8 will do the best job. If it is for serious agricultural research, pH meter and good electrode are the best choice.
General Chemistry Software
www.pH-meter.info
First of all, check this page, as it contains some information about soil pH measurements.
http://www.ph-meter.info/pH-measurements-other-procedures
As for the electrode - you may look for example for pHC2051 made by Radiometer.
Chemical calculators at www.chembuddy.com
www.pH-meter.info
While most of what should be written was already written, let me add one link:
http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations
Browse lectures using menu on the left.