[effofecks]

For my Quant Lab final, we all have to determine the density of acetone. The student with the most significant figures closest to the accepted value of 0.791... g/mL at 20 C is crowned King or Queen of the lab. (However ± 0.004 g/mL is good enough to get full points)

We have volumetric glassware and analytical balances (most have precision of ± 0.1 mg, there is one with ±0.01 mg but it takes a while to settle on a value). The approach I'm thinking of taking currently is to use my largest volumetric pipette (25 mL) and weigh it into a tared 125 mL erlenmeyer flask with cork. From there divide mass by volume and shabam: density. 

I'm wondering if taking into account temperature (the lab is usually 22 C) and buoyancy of air will add accuracy, or just increase my relative standard error? Is there a something I could include in my procedure that would help me?

[Amnesiac_00]

What is more important in this final - accuracy or precision?

Correcting for buoyancy may change your mean and standard deviations. Go through the math with generic numbers (that you can obtain) to see how it affects you final calculations.

[Irlanur]

if accuracy is the deciding factor, I would do a "calibration curve". take several volumes and measure the corresponding mass. the slope (mass/volume) is the density. to get many significant figures, you could just take 3 points that are far away from each other (even orders of magnitude). I never tried this but I would assume it's worth a try.

[jeffmoonchop]

acetone is quite volatile and the larger the surface area of the liquid on a balance the quicker it will evaporate and the more inaccurate your balance reading. It will keep decreasing. If you are set on using 25ml I would use a small conical flask with a narrow top to minimise the surface area and evaporation.

I would repeat the weighing at least ten times to ensure precision and make sure you use a dry flask each time. Residual solvent can tare your balance at a higher value then evaporate before you place the next sample into it making it inaccurate. You can easily do this using your calculation to see if you get a good value.

[jeffmoonchop]

Also you'd be surprised how much leaning on the bench next to your balance affects the balance reading. once you place the acetone in the flask stand away. Once settled after a few seconds, if the reading starts to slowly decrease its evaporating so I would take the highest value before it starts decreasing. I've had far too much experience weighing things  hope it helps