Problem 5.8: A boiler sample shows Palkalinity 400 ppm and

From Chapter 5 Problem Set. Level 3: System Integration.

Question

A boiler sample shows P-alkalinity = 400 ppm and M-alkalinity = 450 ppm (both as CaCO₃). Identify the species present, calculate the OH– alkalinity, and estimate the pH. Remember that for hydroxide, eq/L = mol/L.

Answer

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½M = 225. Since P (400) > ½M (225), hydroxide + carbonate are present. OH– alk = 2P − M = 800 − 450 = 350 ppm as CaCO₃. [OH⁻] = 350 / 50,000 = 0.0070 eq/L = mol/L. pOH = −log10(0.0070) = 2.15. pH = 14 − 2.15 = 11.85.