lab 4
In the lab when pH was measured in water and then with 0.01 M CaCl2, why was the exchangeable acidity lower than the active? Is it because of the buffering capacity of the soil?
Thanks.
Sarah, try not to mix concepts
Buffer capacity is the ability of a soil to resist a change in pH. See lecture 15, slides 11 & 12.
Exchangeable acidity (measured in CaCl2) is lower than active acidity (measured in water). In the lab when you add H2O, you are measuring the H+ and Al3+ ions in soil solution. When you add CaCl2, the Ca replaces H+ and Al3+ on the exchange complex (by mass action); i.e. H+ and Al3+ previously on the exchange complex are "driven" into soil solution, so the pH goes down (i.e. more acidic). See slides 9 & 10.
SandraBrown (talk)