Knowledge Needed Flashcards
What is the difference between a dilute and concentrated solution?
A dilute solution is one in which there is a relatively small amount of solute dissolved in the solution. A concentrated solution contains a relatively large amount of solute
What is weighing by difference?
This procedure involves repetitive weighings of a weighing bottle containing a quantity of solid reagent
What are the steps to prepare the weighing?
Place in a clean, dry glass weighing bottle an amount of solid reagent estimated
to be sufficient for all necessary weighings.
Dry the weighing bottle and contents as instructed
Cool the weighing bottle and contents in a desiccator with fresh desiccant.
Calculate the allowable mass range of your solid reagent appropriate for the
determination at hand.
What are the steps for the weighing process?
- Take the following to the balance room.
- Desiccator with weighing bottle inside.
- A number of beakers or Erlenmeyer flasks equal to
the number of determinations to be done. - Your laboratory notebook.
- Always use the balance assigned to you.
- Place the weighing bottle carefully on the balance pan
- Record the mass in your notebook.
- Remove the weighing bottle and transfer a quantity of the solid reagent to the beaker
or flask in which you will perform the determination. - Replace the weighing bottle on the balance pan and record the new mass
- Repeat these steps for each sample
What are the steps after the weighing process is done?
Replace the weighing bottle (stopper on its side) in the desiccator
Clean up your balance station.
What is the most common method for obtaining a standard solution?
It involves preparation of a solution that has the approximate concentration desired (usually within 10%), determination of the concentration by direct titration against a primary standard, and a test of the accuracy of your determined concentration by comparison with a known standard.
Why must a burette & pipette be rinsed with the appropriate solution?
This step isn’t just a sacred ceremony or a special chemistry ritual – by rinsing the burette, you make sure the concentration of the solution inside will be exactly what you expect it to be. Rinsing with solution actually serves a simple but very practical purpose.
What is the correct procedure for a titration?
Add a known volume of the acidic solution into a conical flask using a pipette.
Add a few drops of phenolphthalein indicator to the conical flask.
Fill a burette with the basic solution to the highest calibration mark.
Use the burette to add the basic solution to the acidic solution until the equivalence point is reached, indicated by a change in indicator colour from colourless to red.
Record the volume of acidic solution used to reach the equivalence point.
Repeat the above procedure several times, slowing the transfer rate from the burette when the previously transferred volume is neared.
Using the concentration of the basic solution, the volumes of both solutions, and the equation of the neutralisation reaction, determine the concentration of the acidic solution.
What are the steps to calculating the dilute concentration?
Calculate the amount of titrant in moles
Find the amount of analyte in moles
Calculate the concentration of analyte in mols/dm^3
Calculate the concentration of the analyte in g/dm^3
How do you calculate the original concentration?
Weigh the amount of solute in grams.
Measure the amount of the solvent that you have
Divide the moles of solute found in Step 1 by the liters of solvent found in Step 2 to find the initial concentration of a solution.
What is the most common technique in cleaning glassware?
The most common procedure that will be effective against most dirty glassware will be to first rinse with an organic solvent, and then second, to wash and scrub with warm, soapy water. Then the glassware needs to be rinsed with tap water, deionized water, and finally with acetone before placing on a rack to air dry.
What is a burette?
A graduated glass tube with a tap at one end, for delivering known volumes of a liquid, especially in titrations
How does a pipette work?
The liquid is taken up into a disposable pipette tip and then dispensed. The piston moves the air cushion and the liquid is thus taken up into the pipette tip or dispensed out of it. The air cushion thus works like an elastic spring, to which the liquid sticks.
What is a volumetric flask?
A volumetric flask is a piece of laboratory glassware, a type of laboratory flask, calibrated to contain a precise volume at a particular temperature.
What are weighing bottles?
Weighing bottles are glass laboratory equipment used for precise weighing of solids. Most of the glass used in the bottles is thin and fragile glass, but sometimes they are also made of ceramics or plastics.
