What indication in the "test tube test" (procedural step 9) will be given if Na3PO4 is the limiting reagent? What if BaCl2 is the limiting reagent? Explain why

Principles of Instrumental Analysis
7th Edition
ISBN:9781305577213
Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Chapter33: Automated Methods Of Analysis
Section: Chapter Questions
Problem 33.5QAP: Give the advantages and disadvantages of sequential injection analyzers compared to traditional flow...
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What indication in the "test tube test" (procedural step 9) will be given if Na3PO4 is the limiting reagent? What if BaClis the limiting reagent? Explain why

Materials:
Bunsen Burner
Ring stand
Wire mesh
100 mL graduated cylinder (2)
250 mL beakers (2)
150 mL beaker
Test tubes (2)
Test tube rack
Glass stir rods (2)
Filtering funnel
Plastic transfer pipet
250 mL Erlenmeyer flask
Note: You will run two samples simultaneously. Perform the procedures for both samples.
Obtain approximately the same volume of the same unknown samples for both trials.
1. Label the graduated cylinders with labelling tape. One will be used for the BaCl2 solution and
the other for the Na3PO4 solution.
2. Obtain approximately 20 mL each of an unknown BaCl2 and Na3PO4 solutions. Record the
volumes (to the correct number of significant figures) in your notebook.
3. In the 250 mL beaker, combine the 20 mL samples of BaCl2 and Na3PO4 solutions and 100 mL
of deionized water. Stir each trial solution for 3 minutes. When finished stirring, remove the
stir rod from the beaker, cover with a watch glass, and allow the precipitate to settle.
4. While the precipitate is settling, set up the ring stand with wire mesh, light the Bunsen burner,
and adjust the flame to a blue flame (with no traces of yellow). Place one sample on the wire
mesh and digest the precipitate for 15 minutes. Do not let the mixture come to a boil! The
goal is to simply gently heat the reaction mixture. Remove the first sample from the ring stand
after 15 minutes and digest the second sample for 15 minutes.
5. After both reactions have finished digesting, heat about 100 mL of deionized water to 70-80
°C in the 150 mL beaker. This water will be used for washing the precipitate out of the beakers
and for washing precipitate off of the stir rods.
6. Set up the filtration apparatus. Obtain 2 sheets of fine porosity filter paper. Using pencil, write
your initials and sample number on each paper. Fold each piece of filter paper into quarters.
Then, open the filter as shown in Figure 6.1. Place the first filter paper in the filter funnel, and
fix it there by wetting it with some deionized water. Allow the deionized water to flow into
the 250 mL Erlenmeyer flask and discard the water.
Transcribed Image Text:Materials: Bunsen Burner Ring stand Wire mesh 100 mL graduated cylinder (2) 250 mL beakers (2) 150 mL beaker Test tubes (2) Test tube rack Glass stir rods (2) Filtering funnel Plastic transfer pipet 250 mL Erlenmeyer flask Note: You will run two samples simultaneously. Perform the procedures for both samples. Obtain approximately the same volume of the same unknown samples for both trials. 1. Label the graduated cylinders with labelling tape. One will be used for the BaCl2 solution and the other for the Na3PO4 solution. 2. Obtain approximately 20 mL each of an unknown BaCl2 and Na3PO4 solutions. Record the volumes (to the correct number of significant figures) in your notebook. 3. In the 250 mL beaker, combine the 20 mL samples of BaCl2 and Na3PO4 solutions and 100 mL of deionized water. Stir each trial solution for 3 minutes. When finished stirring, remove the stir rod from the beaker, cover with a watch glass, and allow the precipitate to settle. 4. While the precipitate is settling, set up the ring stand with wire mesh, light the Bunsen burner, and adjust the flame to a blue flame (with no traces of yellow). Place one sample on the wire mesh and digest the precipitate for 15 minutes. Do not let the mixture come to a boil! The goal is to simply gently heat the reaction mixture. Remove the first sample from the ring stand after 15 minutes and digest the second sample for 15 minutes. 5. After both reactions have finished digesting, heat about 100 mL of deionized water to 70-80 °C in the 150 mL beaker. This water will be used for washing the precipitate out of the beakers and for washing precipitate off of the stir rods. 6. Set up the filtration apparatus. Obtain 2 sheets of fine porosity filter paper. Using pencil, write your initials and sample number on each paper. Fold each piece of filter paper into quarters. Then, open the filter as shown in Figure 6.1. Place the first filter paper in the filter funnel, and fix it there by wetting it with some deionized water. Allow the deionized water to flow into the 250 mL Erlenmeyer flask and discard the water.
Figure 6.1 Opened filter paper to place into filter funnel.
7. Stir up your reaction vigorously before filtering. Decanting the liquid into the filter paper first
will actually result in most of the solid flowing through the pores of the paper.
8. Filter the first sample through the first filter paper. Transfer all of the precipitate by using a
rubber policeman (rubber or TeflonTM spatula) and no more than three 5 mL aliquots of the
warmed wash water. Be sure to collect as much of the precipitate as possible. When the
filtration is complete, carefully remove the filter paper to a clean watch glass for drying in a
safe place until the next laboratory period.
9. Use the plastic transfer pipet to half-fill each of the two centrifuge tubes with the liquid
filtrate. Only centrifuge the samples if necessary. Label the tubes I and II. Add 2 drops of BaCl2
test reagent to tube I, and 2 drops of Na3PO4 test reagent to tube II. You should see an obvious
precipitation reaction in only one of the tubes.
10. Discard the filtrate (the liquid in the receiving flask) from the first sample into the liquid waste
container and rinse the flask 3 times with deionized water. Use the second filter paper to
filter the second sample in identical fashion to the first.
11. Remove the filter paper from the funnel, unfold, and place on a watch glass. The sample
should be placed in the oven for about 15 minutes to dry.
12. Record the mass of the dried filter paper and precipitate.
Waste
All liquid waste can go in the aqueous waste container. Solid waste can be placed in the solid
waste container.
Clean up
Rinse all glassware thoroughly with deionized water. Dry all glassware and return to the
proper place.
Transcribed Image Text:Figure 6.1 Opened filter paper to place into filter funnel. 7. Stir up your reaction vigorously before filtering. Decanting the liquid into the filter paper first will actually result in most of the solid flowing through the pores of the paper. 8. Filter the first sample through the first filter paper. Transfer all of the precipitate by using a rubber policeman (rubber or TeflonTM spatula) and no more than three 5 mL aliquots of the warmed wash water. Be sure to collect as much of the precipitate as possible. When the filtration is complete, carefully remove the filter paper to a clean watch glass for drying in a safe place until the next laboratory period. 9. Use the plastic transfer pipet to half-fill each of the two centrifuge tubes with the liquid filtrate. Only centrifuge the samples if necessary. Label the tubes I and II. Add 2 drops of BaCl2 test reagent to tube I, and 2 drops of Na3PO4 test reagent to tube II. You should see an obvious precipitation reaction in only one of the tubes. 10. Discard the filtrate (the liquid in the receiving flask) from the first sample into the liquid waste container and rinse the flask 3 times with deionized water. Use the second filter paper to filter the second sample in identical fashion to the first. 11. Remove the filter paper from the funnel, unfold, and place on a watch glass. The sample should be placed in the oven for about 15 minutes to dry. 12. Record the mass of the dried filter paper and precipitate. Waste All liquid waste can go in the aqueous waste container. Solid waste can be placed in the solid waste container. Clean up Rinse all glassware thoroughly with deionized water. Dry all glassware and return to the proper place.
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