# Diluting Solutions Lab

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Diluting Solutions Lab
Unit 6
Part 1 Background:
Volumetric asks (see gure) are designed for easy and accurate preparation of
solutions of a given volume. The ask is easily swirled to mix the contents if the
liquid level is below the neck. The volume measurement at the ll line is very
accurate. The asks can be stoppered with a cap for long term storage of solutions.
Procedure — work as accurately as possible!
1. Obtain a 100 mL volumetric ask.
2. Calculate the mass (grams) of solid NaCl necessary to prepare 100 mL of a 0.50 M
NaCI aqueous stock solution. Show your work in the calculation section.
3. Use a weigh boat (partially folded) to add the NaCI solute to the dry volumetric ask.
4. Fill the ask about halfway with tap water. Be sure to rinse any solute stuck in the
neck down into the ask. Swirl to dissolve the solute.
5. Add solvent carefully to the marked line on the neck of the ask. For the most
accuracy, the last drops are best done with a pipette.
6. Invert the ask several times for nal mixing. Make sure the cap is on!
7. Check in with Mr. Ta for any feedback and a stamp (credit for doing the lab)!
Stamp!
Calculation section:
Calculate the mass (in grams) of solid NaCl necessary to prepare 100 mL of a 0.50 molar aqueous solution of NaCl.
Analysis:
(1) What is the solute in this solution? What is the solvent?
(2) In your own words, describe the steps you took to make your solution.
(3) Why do you not ll the ask to the line, and then add the solute?
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Optional Extra Credit Challenge:
(★) What is the percent by mass of the NaCl in your stock solution? (Hint: Assume masssolution = 100g)
Part 2 Background:
Dilutions are prepared by adding extra solvent to a solution of known concentration (also called a &quot;stock&quot; solution)
to reduce the concentration of solute. The amount of stock solution needed is calculated from M1V1=M2V2.
Procedure — work as accurately as possible!
1. Obtain a 250 mL volumetric ask
2. Calculate the volume (mL) of 0.50 M NaCl stock solution needed to make 250 mL of a diluted
solution with a concentration of 0.03 M. Show your work in the calculations section.
3. Using graduated cylinder, measure and pour the appropriate volume of your stock solution
into the new volumetric ask. Use a funnel to pour your solution into the ask if necessary.
5. Invert the ask a few times to mix. Make sure that the cap is on! Double check: see if solution
is at the line. Mixing occurs easily since two liquid phases are being combined.
6. Check in with Mr. Ta for any feedback and a stamp (credit for doing the lab)!
7. Dispose of the solutions down the sink. Rinse out all glassware used in this lab.
Stamp!
Calculation section:
Calculate the volume (mL) of 0.50 M NaCl stock solution needed to make 250 mL of a diluted solution with a
concentration of 0.03 M.
Analysis:
(1) Why is the second solution called “diluted”?
(2) Describe the steps you took to make this solution.
(3) What did you learn from doing this lab?
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Optional Extra Credit Challenge:
(★★) What is the percent by mass of the diluted solution? (Hint: Assume masssolution = 250g)
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