2
$\begingroup$

How does one accurately dose powders? I would like to know what tools are used and how.

For example, how would one apply 1 gram of a certain powder to a solution in a beaker? Specifically, how do you make sure all of your measured powder (or at least with a very small error margin), gets into the solution, without too much of the powder sticking to the spoon or other utensil.

I figured one might dip a spoon loaded with the powder in the solution, but then the solution might stick to the spoon.

Improve this question
$\endgroup$
4
  • 1
    $\begingroup$ During all the laboratory practicals I been to, we've always ignored the bit of 'powder' (we normally deal with salts though) that sticks to the spatula or scoopula.....because it is negligible under most circumstances. Then again if you're conducting a very sensitive test, using a very small quantity of 'powder', then it would advised to (not always though..) finally stir the solution with the scapula you used to transfer the 'powder' to the beaker in the first place. You mentioned that the solution might stick to the spoon (a very astute observation), but even that's negligible...... $\endgroup$
    – paracetamol
    Oct 7, 2016 at 12:20
  • $\begingroup$ ^ have a look at your spoon after you're done stirring sugar into your lemonade...how much of the solution do you see sticking to it? A very small amount....and remember, most of the time, that little bit of solution, will have an even smaller amount of the 'powder' in it..... As for 'dosage' .....you weigh it in grams and over the course of your experiment, you gradually whittle it down to 'moles'........I'd make this into an answer if you'd like..... $\endgroup$
    – paracetamol
    Oct 7, 2016 at 12:26
  • $\begingroup$ Sure, that sounds like a reasonable answer. :) $\endgroup$
    – Protector one
    Oct 7, 2016 at 13:12
  • $\begingroup$ Two things matter if you need accurate concentrations of reagents: your ability to weigh things precisely and your glassware. You can ignore powder sticking to spatulas by weighing the vessel before and after addition of the solid. You can dispense accurate volumes of liquid if the vessel is a calibrated volumetric flask (long thin neck with calibration line for specified volume marked on the thin neck). $\endgroup$
    – matt_black
    Oct 7, 2016 at 15:38

1 Answer 1

Reset to default
2
$\begingroup$

This is how I did it in my analytical practicals, works for primary standards with a decent accuracy, works for everything else with a larger error. (You'd want to check concentrations with a primary standard then.)

  1. Determine the mass of the empty volumetric flask
  2. Prepare approximate mass of the substance you want the solution of in a beaker or watch glass or similar
  3. Transfer the prepared substance into the volumetric flask
  4. Determine the mass of the filled flask; the difference will give you the mass of the substance
  5. Fill the flask with the solvent.
  6. Given the precision of the instruments used, you can calculate the concentration quite accurately. If necessary check the concentration with another method.
Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.