Two, atleast to me, perplexing chem problems

[relativitydude]

1) Calculate the pH at the equivalence point in titrating 0.10 M solution of HBR with 0.08 M NaOH

I know how to do the problem if volume amounts are included. I don't know how many liters are used and consequently the number of moles. Should I just invent some volume for one and calculate the pH based on how much the other takes to titrate it?

2)I need to calculate the equilibrium constant for

Ag2S + 4CL + 2H <---> 2AgCl2 + H2S

The only information provided is Kf (what the heck is Kf?) is 1.1x10^5 for AgCl2

How does one proceed? Thanks! :)

 

[Borek]

Calculate the pH at the equivalence point in titrating 0.10 M solution of HBR with 0.08 M NaOH

I know how to do the problem if volume amounts are included. I don't know how many liters are used and consequently the number of moles. Should I just invent some volume for one and calculate the pH based on how much the other takes to titrate it?

You may try with volumes - say - Va and Vb (for acid and base) - and do the symbolic calculations first. Volumes will cancel out at the end, as the only important thing here is the ratio of concentrations - to neutralize Va HBr solution you need 0.1/0.08*Va NaOH solution, so total volume at the end is (1+0.1/0.08)Va and so on.

Try my BATE (see footer for link) for such calculations of pH and titration curve.

Ag2S + 4CL + 2H <---> 2AgCl2 + H2S

The only information provided is Kf (what the heck is Kf?) is 1.1x10^5 for AgCl2

Kf stands probably for complex formation constant. Next time write the equation with all charges, it will be much easier to understand. I wonder if it is possible to find answer without Ksp for Ag2S and Ka1, Ka2 for H2S... Ksp for AgCl s not a problem, as it is easy to remember (1e-10).


Chemical calculators for labs and education
BATE - pH calculations, titration curves, hydrolisis

 

[GCT]

1) Calculate the pH at the equivalence point in titrating 0.10 M solution of HBR with 0.08 M NaOH

You're asked for the pH. It'll be 7 at equivalence point. The equivalence point is when all of the strong acid/base has reacted with the strong base/acid. Perhaps HBr isnot considered a strong acid, then you'll need to know the Ka.

2)I need to calculate the equilibrium constant for

Ag2S + 4CL + 2H <---> 2AgCl2 + H2S

The only information provided is Kf (what the heck is Kf?) is 1.1x10^5 for AgCl2

How does one proceed? Thanks! :)

I believe what you can do here to is to multiply the Kf by 2