Question

What is the concentration of H3O+ ions in saliva if [OH-] = 4.22 x 10-10 M? Provide the pH and the classification of this sample of saliva.

Answer 1

pH=4.625

The classification of this sample of saliva : acid

Further explanation

The water equilibrium constant (Kw) is the product of concentration

the ions:

Kw = [H₃O⁺] [OH⁻]

Kw value at 25° C = 10⁻¹⁴

It is known [OH-] =  4.22 x 10⁻¹⁰ M

then the concentration of H₃O⁺:

$\tt 10^{-14}=4.22\times 10^{-10}\times [H_3O^+]\\\\(H_3O^+]=\dfrac{10^{-14}}{4.22\times 10^{-10}}=2.37\times 10^{-5}$

pH=-log[H₃O⁺]$\tt pH=5-log~2.37=4.625$

Saliva⇒acid(pH<7)