What Steps Are Needed for Determining Molar Mass by Titration?

[adhiluhur]

In lab I have.
200 mL of a standardised solution of NaOH (of appoximately 0.1 molar concetration)
labeled sample tube containing unknown acid or unknown base.
Indicator: phenolphthalein, Universal, methyl orange.

The aim of this laboratory is to determine the molar mass of an unknown acid by titration, and demonstrate the ability to choose laboratory equipment to allow you to perform a titration.

My questions are:
1. How will you confirm that your unknown sample is an acid.
2. How will you quickly, and accurately, weigh a sample of your unknown solid into appropiately, named, piece of laboratory equipment.
3. What solvent do you think would be most appropriate for the titration (the volume of solvent that should be used, and whether this volume should be accurately measured or approximately measured should be addressed when you discuss this point).
4. What steps should be taken to ensure that all of the unknown solid has dissolved.
5. What equipment, and other chemicals, might be used and how they should be used in the titration.
6. The measurement that must be recorded to enable you to determine the molar mass of your unknown sample and how you calculate error percentage.

 

[symbolipoint]

From adhiluhur:

1. How will you confirm that your unknown sample is an acid.

Use a pH meter if this is allowed. If not, then check your textbook or a reference book on the colors expected for different pH's for each indicator which you have available.

2. How will you quickly, and accurately, weigh a sample of your unknown solid into appropiately, named, piece of laboratory equipment.

As part of titration planning, knowing approximately what molecular or equivalent weights to expect would be helpful. Start with maybe 0.1 gram to about two decimal places just to try a quick titration, but predict, if possible, how much titrant you'll need.
(Did you need help on the titration analysis calculations? Moles of titrant equals moles of analyte (or should I say, "equivalents" of analyte?))

3. What solvent do you think would be most appropriate for the titration (the volume of solvent that should be used, and whether this volume should be accurately measured or approximately measured should be addressed when you discuss this point).

What level of course are you studying? You probably expect to dissolve the material in water. Probably! Testing solubility would be a good idea first. Would half a gram of sample give a reasonable sized titration? Would this amount of sample dissolve in water? Calculations will help.

Note, that calculations may also indicate if you have a need for making a dilution and take aloquot to titrate.

When you finally know how much sample to titrate, you should use an analyical balance and weight at least to the nearest thousandths place.