1. If the H^{+} concentration is 0.0001 M/l, what is the pH?
pH = - (-4) = 4
or place 0.0001 in your calculator and take the log = -4; since pH is - log, = -(-4) = 4
pOH = 14 - 5 = 9
pH = 4.3
or place 0.00005 in your calculator and take the log = -4.3; since pH is - log, = -(-4.3) = 4.3
4. If the pH is 4.5, what is the pOH?
pH + pOH = 14
pOH = 14 - 4.5 = 9.5pOH = 9.5
5. If a soil has a pH of 4.7, what is the H^{+} concentration of the soil solution?
pH = -log [H^{+}]
4.7 = -log [H^{+}]
4.7 = -(- 5) - 0.3; 10^{0.3}=2.0 (the -5 tells you the number of positions to move the decimal point to the left of 10^{0.3}=2.0)
[H+] = 0.00002 M/l
or place -4.7 in your calculator and take the antilog (often inverse log or 10^{x}) = 0.00002 M/l
6. If a CEC is 20 meq/100 g soil and analyses find 12 meq Ca/100 g, 2 meq K/100 g, 1 meq Mg/100 g, 1 meq Na/100 g, 0.5 meq H/100 g, and 3.5 meq Al/100 g, what is the percentage base saturation?
%BS = meq basic ions/CEC
Basic ions = Ca, Mg, K, NA; Acidic ions = H and Al
meq BS = 12 + 2 + 1 + 1 = 16 meq/100 g soil
CEC = 12 + 2 + 1 + 1 + 0.5 + 3.5 = 20 meq /100 g soil
%BS = 16/20 = 80%
7. Recall that a 90% base saturation in a Midwest soil approximately equals a pH of 6.5. Therefore, this soil's pH would be lower; perhaps 5.8 or so. You may verify this by checking the graph given in lecture that relates pH and % base saturation for various soil components.