Homework Help: chemistry

Posted by jaycab on Thursday, January 20, 2011 at 3:37am.

A. Strong Base

1.) What is the concentration of a solution of KOH for which the pH is 11.89?

2.) What is the pH of a 0.011M solution of Ca(OH)2?

B. Weak Acid

1.) The pH of a 0.060M weak monoprotic acid HA is 3.44. Calculate the Ka of the acid.
2.) The pH of 0.100M solution of weak monoprotic acid HA is 2.85. What is the Ka of the acid?

C. SALT HYDROLYSIS
1.) Calculate the pH of a 0.24M sodium formate (HCOONa) solution. Kb=5.9x10^-11.
2.) Calculate the pH of 0.25M pyridium chloride (C5H5NHCl)solution. Ka=5.9x10^6.

D. COMMON ION EFFECT
1.) What is the pH of a solution that is 0.30M in HCOOH and 0.52M in HCOOK.
Ka of HCOOH=1.7x10^-4.
2.) Calculate the pH of a buffer system containing 1.0M CH3COOH and 1.0M CH3COONa. Ka of CH3COOH=1.8x10^-5.

Please help.... i do not know what to do....

chemistry - Dr Russ, Thursday, January 20, 2011 at 4:47am
Please do not put long lists of questions as it is unlikely that they will all get answered. Have you had go at answering any of them?

1)
if pH =11.89 then
pOH=14-11.89=2.11

(this assumes that Kw=10^-14, i.e. that the solution is at ca 25C)

[OH-]=10^-pOH

2)
if concentration is 0.011M then the OH- concentration is twice this as each mole of CaOH2 yields two moles of OH-

so[OH-]=0.022M

pOH=-log([OH-]/mole litre^-1)

then pH=14-pOH
(same assumption as above)

B
1)
HA<-> H+ + A-
at start
0.060M
at equilibrium
0.06-x x x

if pH=3.44 then x=[H+]=10^-3.44

Ka=[H+][A-]/[HA]
so
Ka=x^2/(0.06-x)

find Ka
chemistry - hhha, Thursday, December 15, 2011 at 8:43am
5yht

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