[orgo814]

1) What is the pH of a solution containing 0.2 g/L sodium carbonate and 0.1 g/L sodium hydrogen carbonate? (Ka1 = 4.1 x 10^-7, Ka2 = 5.6 x 10^-11)

I know to use the henderson-hasselbach equation but I'm unsure of which Ka to use for my pKa. Any insight would be great. I would assume Ka1?

2) What is the standard enthalpy of a reaction for which the equilibrium constant increases by a factor of ten when the temperature is increased from 273 K to 298 K?

I know the equation is lnK2/K1 = -delta H/R (1/T2 - 1/T1). I'm just confused on the wording "increased by a factor of ten". Would I put something like 30 as my K2 and 20 as my K1? Or would I just do the natural log of 10?

[Borek]

I know to use the henderson-hasselbach equation but I'm unsure of which Ka to use for my pKa. Any insight would be great. I would assume Ka1?

You have CO₃^2- and HCO₃^- present in the solution - which Ka value described their equilibrium?

I know the equation is lnK2/K1 = -delta H/R (1/T2 - 1/T1). I'm just confused on the wording "increased by a factor of ten". Would I put something like 30 as my K2 and 20 as my K1? Or would I just do the natural log of 10?

It means K2=10K1.

[orgo814]

I would say ka1 because it only went through one step?

[Borek]

Write both dissociation steps, write Ka for each one. Which contains concentrations of the substances present in the solution?

[orgo814]

CO3(2-) + H2O yields HCO3-. Is that not the first step?

[Borek]

No.

http://www.chembuddy.com/?left=pH-calculation&right=polyprotic-dissociation-constants

[orgo814]

Well then I'm confused as to what it is

[orgo814]

Oh HCO3- yields CO32- so second ionization. First would be starting with h2co3

[Borek]

Exactly.