Do the right thing. [Appropriate units, sig figs, legibility, coherence, ethics,

Question

Do the right thing. [Appropriate units, sig figs, legibility, coherence, ethics, ...] Use textbook or instructor's web pages for needed conversions, constants, values, etc. Use values from random web pages may not be correct and will result in no credit. Give 2 sig figs for all results. Calculate the pH of a 1.50 M solution of HF, a weak acid (K_a = 6.8 times 10^-4) HF + H O H_3O^+ F^- Calculate the pH of a 1.50 M solution of the weak add, hypochlorous acid. (K_a = 2.9 times 10^-8) HClO + H_2O H_2O^+ + Calculate the pH of a 2.50 M solution of hypochlorous acid. A 1.00 M solution of butanoic acid, a weak acid, has a pH of 2.41. Calculate the K_a for butanoic acid. HBu + H_2O H_2O^+ + Bu^- [HBu = C_3H_2COOH] Calculate the pH of a 1.00 M solution of methylamine, a weak base, (K_b = 4.4 times 10) CH_ NH_2 + H_2O CH_ NH^_3 + OH^-

Explanation / Answer

1)

for simplicity lets write weak acid as HF

HF -----> H+ + F-

1.50 0 0

1.50-x x x

Ka = [H+][F-]/[HF]

Ka = x*x/(c-x)

since ka is small, x will be small and it can be ignored as compared to c

So, above expression becomes

Ka = x*x/(c)

so, x = sqrt (Ka*c)

x = sqrt ((6.80E-04)*1.50) = 3.19E-02

pH = -log [H+] = -log (3.19E-02) = 1.50

Answer: 1.50

I am allowed to answer only 1 question at a time

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