An MBC student measures the pH of the Shenandoah River to be 7.91. What is conce

Question

An MBC student measures the pH of the Shenandoah River to be 7.91. What is concentration (in mol/L) of H_3 O^- and OH? Is this water considered basic or acidic? Benzoic acid, C_5H_5COOH occurs in many plants and salts of benzoic acid are used as food preservatives. A student obtains a 0.200 mol/L sample of benzoic acid. What is the pH of the solution? What percent of benzoic acid is ionized? Understanding the high-temperature behavior of nitrogen oxides is essential for controlling pollution generated in automobile engines. The decomposition of nitric oxide (NO) to N_2 and O_2 is second order with a rate constant of 0.0796 M^-1 s-^1 at 737 degree C and 0.0815 M^-1 s-^1 at 947 degree C. Calculate the activation energy for the reaction.

Explanation / Answer

Question 3.

pH = 7.91

find concentration of H3O+ and OH-

apply

pH = -log(H+)

so

[H+] = 10^-pH = 10^-7.91 = 1.23026*10^-8 M

note that

[H+] = [H3O+]

and

[OH-] can be obtained via

Kw = [H3O+][OH-]

Kw = 10^-14 at 25°C

so

10^-14 = (1.23026*10^-8)([OH-])

[OH-] = (10^-14)/(1.23026*10^-8) = 8.12*10^-7 M

since pH > 7

this must be BASIC

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