a student titrates three samples of 0.3% hydrogen peroxide solution made from a bottle of 3% hydrogen peroxide solution dated 10/31/2007. would you expect the calculated molarities of the samples to be higher or lower than the following values:

Question

trial 1: .0015 molar
trial 2: .00135 molar
trial 3: .001425 molar

Answer 1

I found a site on the Internet that says "If you carefully read the label and the MSDS you will see that 3% H2O is 3% by weight". Well, I have a bottle of H2O2 at home and it doesn't say anything about what 3% is. Neither does the MSDS sheet on the web. I looked at every source I could find that sells 3% H2O2 and one of them said they sold 30%, 50% and 70% by weight That still doesn't tell me what the 3% is but if we go with what this guy says about "reading carefully" (his source listed 30% H2O2 as a density of 1.11 g/mL) which makes me think your post of a day or so that "assumes" 1.00 g/mL as density for 3% as reasonable.
So if 3% is 3% w/w that means 3g H2O2/100 g solution. And since it is diluted by a factor of 10 I think the 1.00 g/mL must be very close.
3g H2O2 is 3/34.01 = 0.0882 mols.
Mass of that solution will be 100 g and that will be volume of 0.1L.
M then is 0.0882/0.1 = 0.882
In the 0.3% solution, M = 0.0882 since it has been diluted by a factor of 10.
According to two sources on the net the decomposition of commercial H2O2 is very slow even over long periods of time due to stabilizers that are added to the solution. You may have some information in your course work that gives an indication of how much might be lost versus time; my best educated guess, if these net sources are correct is that the titrated samples would be higher than those listed in the problem. However, you may have some information that will contradict that. Feel free to disagree. I don't have any personal experience.