Homework Help: chemistry

Posted by 1/2 equivalence point on Saturday, July 30, 2011 at 7:25pm.

A 25.00 mL sample of 0.4 M dimethylamine (CH3)2NH is titrated with 0.150 M HCl.

What is the pH at the half-equivalence point?

Not sure what to do here exactly, I'm bad with the titration problems.

I know there are normally a couple tables (finding the number of moles at the equivalence point, using this to find concentrations, etc.) but with titrations I never can seem to get the reactions right.

Also I don't rememer the relevance of the half equilvance point. Is it where pH=pKa? I know there's some relevance to the half equivalence point, I just don't recall what it is.

chemistry - DrBob222, Saturday, July 30, 2011 at 10:38pm
The titration equation is
(CH3)2NH + HCl ==> (CH3)2NH2^+ + Cl^-
Where is the equivalence point? It is
(25.00 x 0.4/0.15) = 66.67 mL so the total volume at the equivalence point will be 66.67 + 25.00 = 91.67 mL. The pH will be determined by the hydrolysis of the salt at the equivalence. The hydrolysis equation is
(CH3)2NH2^+ + H2O ==> (CH3)2NH + H3O^+
Set up an ICE chart.
(CH3)2NH2^+ will be 25.00*0.4000/91.67
(CH3)2NH = (H3O^+) = x
Solve for H3O^+ and convert to pH.

Yes, at the half way point the pH = pKa for an acid. Remember this is a base you are titrating so you want to use pKa for the base and not pKb.

Answer this Question

Related Questions

science - 25 ml sample of 0.150 m solution of aqueous trimethylamine is titrated...
chemistry - Calculate the pH of a 0.35 M solution of dimethylamine, (CH3)2NH.
Chemistry - a 25.0 mL sample of .050 M solution of aqueous trimethylamine is ...
chemistry - A 40 mL sample of 0.25 M NaCHOO is titrated with 0.2 M HCl. What is ...
chemistry - A 40.0 mL sample of 0.150 M Ba(OH)2 is titrated with 0.400 M HNO3. ...
Chemistry - a 25.0mL sample of a 0.100M solution of aqueous trimethylamine is ...
chemistry - Okay so I did this problem, but it seems wrong? I put the answers I ...
Chemistry - For the titration of 25.00 mL of 0.150 M HCl with 0.250 M NaoH, ...
chemistry - A .500 g sample of impure CaO (a solid) is added to 50.0 mL of 0.100...
Chem 1A - A 15.00 g sample of an ionic compound NaA, where A- is the anion of a ...

For Further Reading

First Name:
School Subject:
Answer: