Pharmacy Courses

Weighing Techniques for Liquid Samples

Here are some effective techniques for weighing liquid samples:

Direct Weighing

  • Use a Clean Container: Choose a container that is clean, dry and suitable for the type of liquid you are weighing.
  • Tare the Balance: Place the empty container on the balance and tare it to zero.
  • Add the Liquid: Carefully pour the liquid into the container to the desired amount. Avoid splashing or spilling.
  • Record the Weight: Note the weight of the liquid directly displayed on the balance.

Weighing by Difference

  • Initial Weight: Weigh the container (empty or with desired amount of diluent) and record the weight.
  • Final Weight: Transfer the desired amount of liquid to the container reweigh the original container.
  • Calculate the Difference: Subtract the final weight from the initial weight to determine the amount of liquid used.

Using a Syringe or Pipette

  • Prepare the Syringe/Pipette: Ensure it is clean and appropriate for the liquid volume needed.
  • Tare with Syringe/Pipette: If using a syringe or pipette for precise measurement, tare the balance with the empty syringe or pipette first.
  • Draw the Liquid: Draw the required amount of liquid into the syringe or pipette.
  • Weigh the Filled Syringe/Pipette: Weigh the syringe or pipette filled with liquid if precise measurement is needed.
  • Dispense the Liquid: Dispense the liquid into the container or directly into the reaction vessel.

Using a Volumetric Flask

  • Select the Flask: Choose a volumetric flask appropriate for the volume of liquid being measured.
  • Weigh the Empty Flask: Weigh the empty, clean and dry flask.
  • Add Liquid to Mark: Add the liquid up to the calibration mark on the flask.
  • Weigh the Filled Flask: Weigh the flask with the liquid to get the total weight.
  • Calculate the Weight of Liquid: Subtract the weight of the empty flask from the total weight to obtain the weight of the liquid.

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