Question

QUESTION 4

1. Calculate the...needed to produce a buffer with a pH of 6.50. (K_a of H₂CO₃ is 4.3*10^–7)

   Directions: Type your answers only. You may scan your paper work and send it to me for partial credit if your answer is not correct.

   Your answer should look something like this: Ratio = (your answer)

2. QUESTION 6

3. The pH at the equivalence point during the titration of some sample of NH₃ by HCl is 5.20. What is the reason that pH at the equivalence point of a titration is not 7.0?

   		The pH at the equivalence point corresponds the excess of moles of HCl added.
   		The pH at the equivalence point corresponds the excess of moles of NH3.
   		The pH at the equivalence point corresponds to the hydrolysis of NH4+.
   		The pH at the equivalence point corresponds to the hydrolysis of Cl–.

4. Some indicator has K_a = to 6.3*10^–9. Its un-ionized form is yellow and its conjugate base is red. What color would a solution have at pH = 6.45?

   		Red
   		Orange
   		Green
   		Yellow

5. The sample of 25.0 mL of 0.0100 M HClO is titrated with 0.0200 M KOH. (a) Find the volume of 0.0200 M KOH needed to reach the equivalence point. (b) Calculate the pH at the equivalence point (K_b of ClO^– is 3.0*10^–7).

   Which one of the following combinations cannot function as a buffer solution?

   6)

   		Na2HPO4 and NaH2PO4
   		NaHS and H2S
   		NaHSO4 and H2SO4
   		KHCO3 and H2CO3
   		NH3 and NH4I

6. b)

   Which of the following combinations would be the best to buffer the pH of a solution at approximately 7?

   		Na2HPO4 and NaH2PO4 (Ka = 6.23*10-8)
   		H3PO4 and NaH2PO4 (Ka = 7.52*10-3)
   		Na3PO4 and Na2HPO4 (Ka = 4.8*10-13)
   		KCN and HCN (Ka = 6.17*10-10)

Answer 1