chem A solution of a weak acid was tested with the indicators used in this exper

Question

chem

A solution of a weak acid was tested with the indicators used in this experiment. The colors observed were as follows: What is the approximate pH of the solution? An aqueous solution of NH3 has a pH of 11.6. The ammonia (NH3) molecule is the conjugate base of the NH4+ (called "ammonium") ion. Write the net ionic equation for the reaction that makes an aqueous solution of NH3 basic. (Eq. 5.) The pH of a 0.10 M HOBr solution is 4.8. What is [H+] in that solution? ___M What is [OBr-]? What is [HOBr-]? (Where do the H+ and OBr- ions come from?) ____M; ___M What is the value of Ka for HOBr? What is the value of pKa? ___ ___ Formic acid, HFor, has a Ka value equal to about 1.8 x10-4. A student is asked to prepare a buffer having a pH of 3.90 from a solution of formic acid and a solution of sodium format having the same molarity. How many milliliters of the NaFor solution should she add to 20. mL of the HFor solution to make the buffer? _____mL How many mL of 0.10 M NaOH should the student add to 20 mL 0.10 M HFor if she wished to prepare a buffer with a pH of 3.90, the same as in Problem 4?_____mL

Explanation / Answer

3. pH = -log[H+]

Thus, [H+] = 1.58 x 10^-5M

[OBr-] = [H+] = 1.58 x 10^-5M

[HOBr] = given = 0.10M

H+ and OBr- comes from the partial dissociation of HOBr

HOBr <=> H+ + OBr-

Ka = [H+][OBr-]/[HOBr] = 2.51 x 10^-9

pKa = -log[Ka] = 8.6

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