21. Calculate the [OH in an aqueous solution which is 0.125M NH3 and 0.300MNH4CI

Question

21. Calculate the [OH in an aqueous solution which is 0.125M NH3 and 0.300MNH4CI. The value of K, for NH3 is 1.8 x 10-5 A) 4.3 x 105 M B) 1.8 x 10-5 M C) 7.5 x 10-6 M D) 0.425 M E) 0.125 M 22. For an aqueous solution labeled "0.10 M sodium fluoride," A) the pH is greater than 7 B) the pH is less than 7 C) the pH-1 D) the pH 7 E) the pH 13 23. The curve for the titration of 50.0 mL of 0.020 M CGHCOOH(aq) with 0.100 M NaOH (aq) is given below. Which of the following indicators should be used for the titration? 14 12 10 0 6 01520 Vb(mL) A) thymol blue (pKin 1.7) B) bromocresol green (pKin 4.7) C) phenol red (pKIn 7.9) D) methyl red (pKn5.0) E) alizarin (pKin-11.7)

Explanation / Answer

21.

this is a buffer so

pOH = pKb +log(NH4+/NH3)

pKb = 4.75

substitute values

pOH = 4.75 + log(0.3/0.125) = 5.1302

[OH-] = 10^-poh = 10^-5.1302 = 0.00000740968 = 7.4*10^-6

choose C

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