Question

If the [H⁺] in acid mine drainage is 6.2 x 10^-5 mol/L, the pH of the drainage water is _____ . It would require ______ gallons of 0.15 M Ca(OH)₂ to neutralize the proton acidity in 3000 gallons of such drainage water.

Answer 1

We have H+ concentration and from it we can get pH.   We find H+ concentration in given volume of solution and then we can find concentration of OH-. Once we know the concentration of OH- then we can get concentration of calcium hydroxide.

pH = - log [H+]= - log ( 6.2E-5) = 4.20

Calculation of H+ in 3000 Ga

[H+] = (6.2E-5 mol/ L ) x 3000 Ga x 3.78541 L / Ga

= 0.7041 M (mol/L)

Neutralization reaction

H+ + OH- ---- > H2O

[Ca(OH)2] = 1/2 x [OH-] = 2 x (0.7041M ) = 0.35 M

Concentration of calcium hydroxide needed = 0.35 M