[baigsabeeh]

My lab partner and I are going crazy trying to complete this one lab we have to do for the local Chemistry Olympics competition.  The link below shows the event description.

http://www.geocities.com/njco2008/event9.htm

My lab partner and I have been using standard techniques for microscale titration.  We set up two 25ml burets, one for acid and one for base.  The base is known.  We're using 1.5 M NaOH.  Just to test our method, we used a known acid, 2 M HCl.  However, we hit a roadblock.  We tried calculating the densities of the base and acid by using a volumetric pipet.  We took 10 ml samples of each and put them in a beaker on a scale that was zeroed with the beaker on it.  The density for the base solution was 10.48 g/ml, for the acid solution 10.26 g/ml.  That means, once you take out the densities for the water, the density for the base is 0.048 g/ml and for acid is 0.026 g/ml.  The problem is that when we worked from those to calculate the molecular mass of the acid and base, we got 33 g and 32 g respectively.  The actual for acid and base is roughly 37 g and 40 g.  I'm quite a bit worried because these means that there's something going on with the water while making the solution.  Do you guys have any ideas as to what might be happening?

We're using universal indicator to track pH and back-titrating to get as close as possible to the equivalence point.  We've got that down pretty well. 

Any other help would be appreciated?  If you guys suggest an alternative method, then I'd be grateful.

[Borek]

The density for the base solution was 10.48 g/ml, for the acid solution 10.26 g/ml.  That means, once you take out the densities for the water, the density for the base is 0.048 g/ml and for acid is 0.026 g/ml.

This is false assumption. Volumes are not additive. Water is OK, your method is completey off. You don't need density of solution, you need to compare mass of the acid used with number of the moles of the acid from titration.

Honestly, this is very basic knowledge. There is a long road ahead you if you want to start in any Chemistry Olympics.

[AWK]

The density for the base solution was 10.48 g/ml, for the acid solution 10.26 g/ml. 

Density of solution?
Such densities show molten metallic lead, not a water solutions