48. Consider a buffer solution containing HCN and NaCN where the concentration o

Question

48. Consider a buffer solution containing HCN and NaCN where the concentration of HCN is double the concentration of NaCN. Which statement about the buffer solution is true The pH of this solution is equal to the pKa value of HCN (A) The pKa value of HCN will decrease if a strong acid is added. (B) The buffer capacity of this solution will improve if a strong acid is added. (C) The cyanide ion concentration will increase if a strong base is added. (D) If 25.0 mL of 0.750 M HCI are added to 100. mL of 0.352 M NaOH, what is the final pH? The volumes are additive. 49. (A) 13.45 (B) 13.12 (C) 7.00 (D) 0.40

Explanation / Answer

48) ph of acdic buffer = pka + log(NaCN/HCN)

   NaCN/HCN = 1/2

if base is added, concentration of NaCN increases, HCN-decreases

answer: D

49) molarity of mixture = M1V1-M2V2/V1+V2

                = (((100*0.352)-(25*0.75))/(100+25)

                = 0.1316 M

pH = 14 - (-log(OH-))

    = 14 - (-log0.1316)

    = 13.12

answer: B

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