Consider the titration of a 26.2 mL sample of 0.125M RbOH with 0.105M HCl. Deter

ID: 841045 • Letter: C

Question

Consider the titration of a 26.2 mL sample of 0.125M RbOH with 0.105M HCl. Determine each of the following:

A. the initial pH (Express your answer using two decimal places.)

B. the volume of added acid required to reach the equivalence point

C. the pH at 5.8mL of added acid (Express your answer using two decimal places.)

D. the pH at the equivalence point (Express your answer as a whole number.)

E. the pH after adding 5.8mL of acid beyond the equivalence point (Express your answer using two decimal places.)

Thanks!

RbOH is strong base and HCl is strong acid , hence both dissociate completly to give OH- and H+ ions

A) initial pH = 14+log [OH-] = 14 -log ( 0.125) = 13.1

B) at equivalence point acid moles = base moles , hence 0.105 x V = 0.125 x 26.2

V = 31.2 ml

C) acid moles added = MV = 0.105 x 5.8/1000 = 0.00061

now net base moles = ( 0.125x26.2/1000) - 0.00061 = 0.002665

vol = 5.8+ 26.2 = 32 ml = 0.032 L ,

now [OH-] = 0.002665/0.032 = 0.0833

pH = 14 +log ( 0.0833) = 12.92

D) at equivalence point pH = 7 ( neutral)

E) excess H+ moles = ( 0.105x5.8/1000) = 0.000609

total vol = ( 26.2 + 31.2+5.8) = 63.2 ml = 0.0632 L

[H+] = ( 0.000609/0.0632) = 0.009636

pH = -log ( 0.009636) = 2.02

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