November 29, 2015

Homework Help: Chemistry

Posted by John Peterson on Wednesday, May 23, 2007 at 8:53am.

Calculate soln pH if 100 mL 0.10 M Na2S is mixed with 200 mL 0.050 M HCl. The hint is consider Kb for HS^-. The answer is pH=9.74. Can someone walk me through the neccessary steps to get this answer?

What are the k1 and k2 values for H2S in your text?

Sorry I'm just now responding, I thought I figured it out but my approach was still wrong. Anyways, the K acid value=1.1*10^-7, therefore K conjugate base (HS^-) value= 9.09*10^-8. Because these are bronstend-lowry/acid-base rxns I understand its neccessary to write a principle rxn equation to determine what IONS/ACIDS/BASES are present in solution upon mixing sodium sulfide and HCl acid. What I figure so far is this: Na2S dissociates in Na^+ and S^2-. The sulfide ion reacts with water as a base to produce HS^- and OH^-. Both these rxns go to a large extent and are therefore exist in solution. Likewise, HCl (a strong Bronstend lowry acid) inventories into H30^+ and Cl^-. That is where I got, but now I'm stuck. I would assume that some of the ions can act as bases/acids, and react further, but I'm not completely sure... Thank you

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