Answer to Question #154985 in Chemistry for Alexis

Question

Calculate the molar concentration of hydrogen ions in solution: (a) pH = 2.8 and (b) pOH = 4.2?

Answer 1

[H⁺] is the molar hydrogen ion concentration (in mol L^-1 or M).

Solution:

(a):

pH is defined as the negative logarithm of the hydrogen ion concentration:

pH = -log[H⁺]

Hence, [H⁺] can be calculated using the above equation:

[H⁺] = 10^-pH

[H⁺] = 10^-2.8 = 0.001585 M = 1.6×10^-3 M

[H⁺] = 1.6×10^-3 M

(b):

For any aqueous solution at 25^∘C:

pH + pOH = 14

Hence,

pH = 14 - pOH = 14 - 4.2 = 9.8

pH is defined as the negative logarithm of the hydrogen ion concentration:

pH = -log[H⁺]

Hence, [H⁺] can be calculated using the above equation:

[H⁺] = 10^-pH

[H⁺] = 10^-9.8 = 1.585×10^-10 M = 1.6×10^-10 M

[H⁺] = 1.6×10^-10 M

Answer:

(a): [H⁺] = 1.6×10^-3 M

(b): [H⁺] = 1.6×10^-10 M