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2506 Quantitative Reactions

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    440572
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    QUANTITATIVE REACTIONS

    1.0 INTRODUCTION

    A limiting reagent (sometimes called limiting reactant) is the reagent that is completely consumed during a chemical reaction. Once this reagent is consumed the reaction stops. An excess reagent (sometimes called excess reactant) is the reactant that is left over once the limiting reagent is consumed. The maximum yield of a chemical reaction is dependent upon the limiting reagent thus the one that produces the least amount of product is the limiting reagent.

    In class, stochiometric calculations are used to identify the limiting and excess reagents. In lab, we can identify the limiting and excess reagents experimentally. In this experiment you will be create a mixture of two ionic solutions, Co(NO3)2 and Na3PO4. When the solutions are mixed, they will react to form an insoluble salt, which can be separated from the liquid.

    Precipitate is the term used for an insoluble solid which is produced by mixing two solutions. The liquid above the precipitate is called the supernatant. When the mixture is poured into a filter, the solid precipitate is trapped by the filter and the liquid supernatant passes through as the filtrate. You will then test the filtrate to find out the limiting reagent.

    2.0 SAFETY PRECAUTIONS AND WASTE DISPOSAL

    !!Wear your safety goggles!!

    When you are finished with the experiment, place any solid that contains cobalt in the proper container for solid waste.

    Pour any solution that contains cobalt in the proper container for liquid waste.

    Solutions without cobalt may be safely disposed of down the drain.

    3.0 CHEMICALS AND SolutionS

    Chemical

    Concentration

    Approximate amount

    Notes

    Co(NO3)2.6H2O

    N/A

    About the size of a pea (0.25 g)

     

    Na3PO4.12H2O

    N/A

    About the size of a pea (0.25 g)

     

    K3PO4

    N/A

    About the size of a pea or less

     

    CoCl2.2H2O

    N/A

    About the size of a pea or less

     

    NaNO3

    N/A

    About the size of a pea or less

     

    Co(NO3)2 solution

    0.0183g/mL

    90 mL

    Record the exact concentration as printed on the bottle

    Na3PO4 solution

    0.0156g/mL

    60 mL

    Record the exact concentration as printed on the bottle

    4.0 GLASSWARE AND APPARATUS

    Item

    Use

    Notes

    Several beakers of any size

    Preparing and mixing solutions

    Rinse well before reusing a beaker (they do not have to be dry).

    4 funnels

    For gravity filtration

     

    5 sheets(circles) of filter paper

    For gravity filtration

     

    Buret or volumetric pipets of 5.0, 10.0, 15.0, 20.0 mL and bulb

    For careful quantitative measurements of aqueous solutions

    Either set of devices work, check stockroom for availability

    5.0 PROCEDURE

    Careful records of your observations are key to answering questions posed by your investigation. A bound laboratory notebook is one way to secure and maintain your records.

    1. Investigation: Conduct and analyze the chemical reaction between Co(NO3)2 and Na3PO4 (Part 1).
    1. First, let us explore the reaction without doing any careful measurements. In a beaker, dissolve about a pea-sized amount (about 0.25 g) of solid Co(NO3)2.6H2O in approximately 20 mL of laboratory water. Label this beaker “Co(NO3)2 solution”. Record the appearance of the solution (Clear? Cloudy? Colored?) in Data Table 1 in Section 6.
    1. In a second beaker, dissolve about a pea-sized amount (about 0.25 g) of solid Na3PO4.12H2O in approximately 20 mL of laboratory water. Label this beaker “Na3PO4 solution”. Record the appearance of the solution (Clear? Cloudy? Colored?) in Data Table 1 in Section 6.
    1. Start the chemical reaction by transferring about half of each solution into a third beaker and mixing well. Label this third beaker as “Reaction between Co(NO3)2 and Na3PO4”. Record the appearance of the solution (Clear? Cloudy? Colored?) in Data Table 1 in Section 6.
    1. Although you could use solubility rules (a topic discussed in class) to predict the products of today’s reaction, let us instead conduct some additional experiments to determine the identity of the product. In Data Table 1 in Section 6, list the two ions formed when Co(NO3)2 and Na3PO4 dissolves.
    1. Assuming that the reaction involves two ions bonding together, list all possible chemical formulas for the product that might result from the mixing of Co(NO3)2 and Na3PO4 in Data Table 1 in Section 6.
    1. For each chemical formula that you listed, design and conduct a reaction to make the compound with that chemical formula. (Additional chemicals should be available in lab). For example, perhaps Co3(PO4)2 is a product, so try reacting CoCl2.2H2O with K3PO4 to make Co3(PO4)2. List the chemicals used, appearance of each solution and reaction mixture, as well as ions and products of each mixture in Data Table 2 in Section 6. How do these reaction mixtures compare with the contents of the beaker labeled “Reaction between Co(NO3)2 and Na3PO4”.
    1. Filter the mixture from the beaker labeled “Reaction between Co(NO3)2 and Na3PO4”. The liquid obtained after filtration is called the supernatant, and it contains the product that is not a solid. However, we did not measure the reagents carefully, so there may be some leftover reagents also dissolved in the supernatant. Let us find out which reagent, if any, is still present in the supernatant.
    1. Pour half of the supernatant into an empty beaker, and then pour the remainder of the supernatant into a second empty beaker. Pour some Co(NO3)2 solution into the first beaker, and pour some Na3PO4 solution into the second beaker.
    1. In Data Table 3 in Section 6, record your observations and indicate the chemicals present in your supernatant. Did your supernatant contain Co(NO3)2 or Na3PO4 or neither? How do you know?
    1. Investigation: Conduct and analyze the chemical reaction between Co(NO3)2 and Na3PO4 (Part 2).
    1. Now let us repeat today’s reaction by taking very careful measurements.

    Obtain 4 clean beakers and label them #1, #2, #3, and #4. Into each beaker, place 20.0 mL of the 0.0183g/mL Co(NO3)2 solution from the stockroom. Record the actual volume measurements and concentration in Data Table 4 in Section 6.

    Now transfer different amounts of the Na3PO4 solution into beakers #1, #2, #3, and #4. Suggested amounts are 5.0, 10.0, 15.0, and 20.0 mL. Record the the actual volume measurements and concentration in Data Table 4 in Section 6. Mix each solution completely and let sit for at least 5 minutes.

    1. Let us find out which reagent, if any, is still present in the supernatant. Filter each reaction mixture and collect the supernatants into another set of 4 labeled beakers. You do not have to collect all of the supernatant from each reaction but collect at least 10 mL that is devoid of any solids.
    1. Divide each supernatant into 2 portions: into one portion, add at least 5 drops of Co(NO3)2 solution; into the other portion, add at least 5 drops of Na3PO4 solution. Examine each of these new reactions for a precipitate (a solid). The appearance of a solid will help us identify if a reagent was still present in the supernatant. Complete Data Table 5 in Section 6 testing each filtrate.

    1. Now that we know which reagent was present in the supernatant, then the other reagent must have been the limiting reagent! For example, if the supernatant from Beaker #1 produced a solid when Na3PO4 was added, then Na3PO4 must have been the limiting reagent because it was used up first, leaving behind some unreacted Co(NO3)2.

    6.0 DATA RECORDING SHEET

    Last Name

    First Name

    Partner Name(s)

    Date

     
         

    Data Table 1. Qualitative Data Co(NO3)2 + Na3PO4

     
     

    Appearance

    Ions When Dissolved

    Co(NO3)2.6H2O

       

    Na3PO4.12H2O

       
     

    Appearance

    Product Chemical Formulas

    Mixture

       

    Data Table 2. Qualitative Data Reactions to Form Products

    Product Being Formed: ________________

    Chemical Used

    Appearance

    Ions When Dissolved

         
         
     

    Appearance

    Product Chemical Formulas

    Mixture

       

    Product Being Formed: ________________

    Chemical Used

    Appearance

    Ions When Dissolved

         
         
     

    Appearance

    Product Chemical Formulas

    Mixture

       

    Data Table 3. Qualitative Data Supernatant Test

     

    Appearance

    Addition of Co(NO3)2

     

    Addition of Na3PO4

     
     

    Chemicals Present in Supernatant:

    Reasoning:

    Data Table 4. Quantitative Data Co(NO3)2 + Na3PO4

    Concentration of Stock Co(NO3)2 _________________ g/mL

    Concentration of Stock Na3PO4 _________________ g/mL

    Beaker

    Volume (mL) of Co(NO3)2

    Volume (mL) of Na3PO4

    Grams of Co(NO3)2

    Grams of

    Na3PO4

    #1


         

    #2


         

    #3


         

    #4


         

    Data Table 5. The Testing of the Supernatants

    Supernatant from Beaker # 1

    Supernatant from Beaker # 2

    Supernatant from Beaker # 3

    Supernatant from Beaker # 4

    To half of the supernatant, add…

    To half of the supernatant, add…

    To half of the supernatant, add…

    To half of the supernatant, add…

    5 drops of Co(NO3)2

    5 drops of Na3PO4

    5 drops of Co(NO3)2

    5 drops of Na3PO4

    5 drops of Co(NO3)2

    5 drops of Na3PO4

    5 drops of Co(NO3)2

    5 drops of Na3PO4

    Did a solid form?

    Did a solid form?

    Did a solid form?

    Did a solid form?

    Did a solid form?

    Did a solid form?

    Did a solid form?

    Did a solid form?

                 

    If yes, which reagent was still present in Beaker #1?

    If yes, which reagent was still present in Beaker #1?

    If yes, which reagent was still present in Beaker #2?

    If yes, which reagent was still present in Beaker #2?

    If yes, which reagent was still present in Beaker #3?

    If yes, which reagent was still present in Beaker #3?

    If yes, which reagent was still present in Beaker #4?

    If yes, which reagent was still present in Beaker #4?

                 
    1. CALCULATIONS AND DATA ANALYSIS

    7.1 Investigation: Conduct and analyze the chemical reaction between Co(NO3)2 and Na3PO4 (Part 1).

    1. How did the reaction mixtures in Data Table 2 compare with the contents of the beaker labeled “Reaction between Co(NO3)2 and Na3PO4” from Data Table 1? Use and discuss these experimental results to identify the solid formed in the beaker labeled “Reaction between Co(NO3)2 and Na3PO4”.



    1. Now that you have identified the solid formed in the reaction between Co(NO3)2 and Na3PO4, write the BALANCED chemical equation for this reaction. Include physical states in your balanced equation. Your balanced equation should contain two reagents and two products (one product is a solid and one product is aqueous).

    1. Investigation: Conduct and analyze the chemical reaction between Co(NO3)2 and Na3PO4 (Part 2).
    1. Review your results for the “The Testing of the Supernatants” in Data Table 4. Did all four supernatants give the same result? Discuss why or why not.





    1. Now confirm your experimental results by calculating the limiting reagent for each reaction #1, #2, #3, #4. The following data tables will help you with this.

    Beaker 1

    Line 1

    Number of grams of Co(NO3)2 present (refer to Quantitative Data Table 4)

     

    Line 2

    Molar mass of Co(NO3)2

     

    Line 3

    Number of moles of Co(NO3)2 present

     

    Line 4

    Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 3?

     

    Line 5

    Number of grams of Na3PO4 present (refer to Quantitative Data Table 4)

     

    Line 6

    Molar mass of Na3PO4

     

    Line 7

    Number of moles of Na3PO4 present

     

    Line 8

    Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 7?

     

    If Line 8 is larger than Line 3 AND if Line 7 is larger than Line 4, then Co(NO3)2 is the limiting reagent.

    However, if Line 4 is larger than Line 7 AND if Line 3 is larger than Line 8, then Na3PO4 is the limiting reagent.

    Identify the limiting reagent for Beaker #1 _______________

    Beaker 2

    Line 9

    Number of grams of Co(NO3)2 present (refer to Quantitative Data Table 4)

     

    Line 10

    Molar mass of Co(NO3)2

     

    Line 11

    Number of moles of Co(NO3)2 present

     

    Line 12

    Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 11?

     

    Line 13

    Number of grams of Na3PO4 present (refer to Quantitative Data Table 4)

     

    Line 14

    Molar mass of Na3PO4

     

    Line 15

    Number of moles of Na3PO4 present

     

    Line 16

    Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 15?

     

    If Line 16 is larger than Line 11 AND if Line 15 is larger than Line 12, then Co(NO3)2 is the limiting reagent.

    However, if Line 12 is larger than Line 15 AND if Line 11 is larger than Line 16, then Na3PO4 is the limiting reagent.

    Identify the limiting reagent for Beaker #2 _______________

    Beaker 3

    Line 17

    Number of grams of Co(NO3)2 present (refer to Quantitative Data Table 4)

     

    Line 18

    Molar mass of Co(NO3)2

     

    Line 19

    Number of moles of Co(NO3)2 present

     

    Line 20

    Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 19?

     

    Line 21

    Number of grams of Na3PO4 present (refer to Quantitative Data Table)

     

    Line 22

    Molar mass of Na3PO4

     

    Line 23

    Number of moles of Na3PO4 present

     

    Line 24

    Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 23?

     

    If Line 24 is larger than Line 19 AND if Line 23 is larger than Line 20, then Co(NO3)2 is the limiting reagent.

    However, if Line 20 is larger than Line 23 AND if Line 19 is larger than Line 24, then Na3PO4 is the limiting reagent.

    Identify the limiting reagent for Beaker #3 _______________

    Beaker 4

    Line 25

    Number of grams of Co(NO3)2 present (refer to Quantitative Data Table)

     

    Line 26

    Molar mass of Co(NO3)2

     

    Line 27

    Number of moles of Co(NO3)2 present

     

    Line 28

    Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 27?

     

    Line 29

    Number of grams of Na3PO4 present (refer to Quantitative Data Table)

     

    Line 30

    Molar mass of Na3PO4

     

    Line 31

    Number of moles of Na3PO4 present

     

    Line 32

    Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 31?

     

    If Line 32 is larger than Line 27 AND if Line 31 is larger than Line 28, then Co(NO3)2 is the limiting reagent.

    However, if Line 28 is larger than Line 31 AND if Line 27 is larger than Line 32, then Na3PO4 is the limiting reagent.

    Identify the limiting reagent for Beaker #4 _______________

    1. Record the identities of the limiting reagents in the table below.

    Beaker

    Limiting Reagent By Testing the Supernatants

    Limiting Reagent By Calculations

    #1


     

    #2


     

    #3


     

    #4


     

    Do your results make sense? Suggest reasons for any unusual result(s).





















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