Chem - salt problem AJ

[A.J.]

Hi, Can you help me on doing the steps to answer this problem?

 

Given:

Mass of Salt = 10 grams

Total Volume = 1 litres

--> the salt is dissolved into this volume to make a solution.

pH of the Solution = 13.07

--> salt is completely ionized in the solution.

 

Required: Molecular Weight of the salt.

 

Correct me: (given the mass; we need to find the number of mole)

Step 1 - find concentration using the pH.

pH = -log[A], where [A] is the concentration of the solution.

Step 2 - find the number of moles is the solution.

n (# of moles) = Volume (total volume) x Molarity (from step one)

Step 3 - find the molecular weight by dividing the mass by the number of moles.

MW (molecular weight) = mass divided by the # of moles.

[Bluenoise]

You'll need more information than that to answer this question.

Like the starting pH of what your disolving your salt into. Plus there are many molecules that can donate or accept more than one proton/ (electrons)

 

But assuming you're disolving in a non-buffered solution of pH 7. And the molecule only accepts one proton (because it's obviously a base).

Then what you suggest would work for an acid.. But since the pH has raised you will need to find the concentration of the base.

[A.J.]

You'll need more information than that to answer this question.

Like the starting pH of what your disolving your salt into. Plus there are many molecules that can donate or accept more than one proton/ (electrons)

 

But assuming you're disolving in a non-buffered solution of pH 7. And the molecule only accepts one proton (because it's obviously a base).

Then what you suggest would work for an acid.. But since the pH has raised you will need to find the concentration of the base.

 

You are most correct, Bluenoise. Thanks for your response. I got the correct steps, which lead me to the correct answer. As you said, we need to find the concentration of the base, which is correct and is one of the steps that I must solve, that is through using the given pH. And then, once the concentration of the base is found, it is a matter of dimensional analysis to solve this problem. The hint is to end up in an answer with units of 'grams per mol' since we are looking for the molecular weight. Thanks a lot for your response! I appreciate it.

[Bluenoise]

Yeah what did you get? I got ~85 g/mol.

[A.J.]

Yeah what did you get? I got ~85 g/mol.

 

Sorry for the late answer. The site was down in my part for some reason. Yeh, the answer that I got is 85.1 g/mol.