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Part 1 of 1
The pH scale is defined as pH = -log10[H+]. In pure water at 25°C, [H+][OH-] = K_w = 1.0 x 10^-14, so pH + pOH = 14.
Strong acids (HCl, HNO3, H2SO4) dissociate completely in water: a 0.01 M HCl solution has [H+] = 0.01 M = 10^-2 M, giving pH = -log10(10^-2) = 2.0. Neutral solutions have pH = 7.0; acidic < 7.0; basic > 7.0.
Worked example
Find the pH of a 0.001 M NaOH strong base solution. NaOH dissociates completely: [OH-] = 0.001 M = 10^-3 M. Calculate pOH = -log10(10^-3) = 3.0. Calculate pH = 14.0 - pOH = 14.0 - 3.0 = 11.0. Solution is basic.
1.A 0.01 M solution of strong acid HCl has a pH of 2.0.
2.A solution with pH = 9.0 is acidic.
3.In water at 25°C, the sum of pH and pOH always equals 14.0.
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