MasteringChemistry Cour x MasteringChemistry Ch1 V MasteringChemistry: Ch1: x Vé

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MasteringChemistry Cour x MasteringChemistry Ch1 V MasteringChemistry: Ch1: x Vé How to take a screenshot eChegg.com x -> https://session.masteringchemistry.com/myct/itemview?assignmentProblemID=59038236 CHEM 106 McCoy S16 Ch 15 HWExercise 15.112 Signed in as Hunter Paul Help Close Resources « previous | 27 of 29 | next » Exercise 15.112 Part A Calculate the concentration of all species in a 0.155 M solution of H2 CO3 Enter your answers numerically separated by commas. Express your answer using two significant figures Submit My Answers Give Up Incorrect; Try Again; 4 attempts remaining ac Continue

Explanation / Answer

H2CO3 dissociates as follows,

H2CO3 ----> H+ + HCO3- ----------------- Ka1 = 4.5 x 10^-7

HCO3- ------> H+ + CO3 2- ----------------Ka2 = 4.8 x 10^-11

H2CO3 -----> H+ + HCO3-

0.155 - X........X+Y.....X-Y

HCO3- -------> H+ + CO3 2-

X-Y ...............X+Y........Y

Ka1 = (X+Y) x (X-Y) / (0.155-X)

Ka2 = Y (X+Y) / (X-Y)

Since Ka1 >> Ka2, X >> Y, Therefore Y can be neglected with respect to X.

=> 4.5 x 10^-7 = (X) x (X) / (0.155-X)

=> X = 2.64 x 10^-4

and

Ka2 = 4.8 x 10^-11 = Y

[H2CO3] =0.155 - X = 0.1547 M

[HCO3-] = X - Y = X = 2.64 x 10^-4 M

[H+] = X + Y = X = 2.64 x 10^-4 M

[CO3 2-] = Y = 4.8 x 10^-11 M

[OH-] = 10^-14 / 2.64 x 10^-4 = 3.79 x 10^-11 M

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