Posted by Ashley on Thursday, March 15, 2012 at 10:04pm.
A 15.00 g sample of an ionic compound NaA, where A- is the anion of a weak acid, was dissolved in enough water to make 100.0 mL of solution and was then titrated with 0.100 M HCl. After 700.0 mL of HCl was added, the pH was 5.00. The experimenter found that 1.40 L of 0.100 M HCl was required to reach the stoichiometric point of the titration
what is the molar mass of NaA? and
Calculate the pH of the solution at the stoichiometric point of the titration.
- Chem 1A - DrBob222, Thursday, March 15, 2012 at 10:58pm
Look at HA ionization.
HA ==> H^+ + A^-
Ka = (H^+)(A^-)/(HA)
Solve for (H^+) = Ka(HA)/(A^-)
Note that 700 mL is exactly half way to the equivalence point; therefore, we know (HA) untitrated = (A^-) from the half titrated. Thus pKa = pH.
At th stoichiometric point you know mols HCl = M x L = 0.1M x 1.4L = 0.14mols.
That represents 15.00 g;
grams = moles/molar mass. Solve for molar mass.
15.00 g/molar mass = mols NaA and
M = moles/L at this point. I see 1.4L + 100 mL initially used.M = ?
............A^- + HOH ==> HA + OH^-
Kb for A^- = (Kw/Ka for the acid) = (HA)(OH^-)/(A^-)
Substitute from the ICE chart above and solve for x = OH^-, then convert to pH.
Answer this Question
More Related Questions
- College Chemistry - I need help with this question!! a sample of pure KHP ...
- Chemistry - .050 mole of weak acid (HA) is dissolved in enough water to make 1.0...
- chemisrty - A solid acid is dissolved in enough water to make 200 ml of a ...
- Chemistry - A sample of solid Ca(OH)2 is stirred in water at 30°C until the ...
- chem - the pH of a .100 M solution of sodium formate = 8.37. Calculate the value...
- Chem AP - A 0.505-g sample of a compound is dissolved in enough water to form ...
- chemistry - A 125.0 mg sample of an unknown, monoprotic acid was dissolved in ...
- chemistry - We want to make 100. mL of 1.0 M NaA solution by dissolving solid ...
- Chemistry - A 55.29-g sample of Ba(OH)2 is dissolved in enough water to make 1....
- Chemistyr - A 55.29-g sample of Ba(OH)2 is dissolved in enough water to make 1....