Percent Yield Experiment. The limiting reagent for this experiment is strontium chloride hexahydrate. The two products will be strontium sulphate as a solid and copper (II) chloride in an aqueous state.

14. Dry the filter paper over the duration of 24 hours.

15. Record the mass of the filter paper with the dried precipitate using the control scale.

Observations:

Table 1: Recorded mass of the filter paper, the filter paper with the precipitate and finally the mass of the precipitate. Mass values measured on teacher's control digital scale.  

Mass of filter paper (g)

        Mass of filter paper and precipitate (g)

        Mass of precipitate (g)

        1.21

        1.87

        0.66

        

Calculations:

Calculation 1:  Determining the molar mass of strontium chloride hexahydrate

Given:                Mass of strontium                                                        87.62 amu

                Mass of chlorine                                                        35.45 amu

                Mass of hydrogen                                                        1.01 amu

                Mass of oxygen                                                        15.99 amu

Procedure:

                Molar mass        = Sr+(Clx2)+(((Hx2)+O)x6)

                                = 87.62+70.9+108.06

                                = 266.58 g/mol

∴ Therefore the molar mass of strontium chloride hexahydrate is 266.58 g/mol

Calculation 2:  Converting from grams to moles for strontium chloride hexahydrate

Given:                Mass of strontium chloride hexahydrate                                1.00g

                Molar mass of strontium chloride hexahydrate                        266.58 amu

Procedure:

                Moles                = Mass / molar Mass

                                = 1.00/266.58

                                = 3.751x103-

∴ Therefore there are 3.751x103- moles of stronium chloride hexahydrate.

Calculation 3:  Converting from moles to grams for strontium sulphate.

Given:                Moles of strontium sulphate                                                3.751x103-

                Molar mass of strontium sulphate                                        183.64 g/mol

Procedure:

                Grams                = Moles x molar mass

                                = 3.751x103- x 183.64

                                = 0.6888 g

∴ Therefore there is 0.6888 grams of strontium sulphate

Calculation 4:  Percent Yeild

Given:                Mass of strontium sulphate precipitate                                 0.66 g

                Theoretical mass of strontium sulphate                                0.6888 g

Procedure:

                Yeild                = (Experimental mass/theoretical mass) x 100

                                = 0.9582 x 100

                                = 95.82 %

∴ Therefore the percent yeild of strontium sulphate in this experiment is 95.82 %

Calculation 3:        Percent Error

Given:                Mass of strontium sulphate precipitate                                0.66 g

                Theoretical mass of strontium sulphate                                 0.6888 g

Procedure:

                Error                = ((Theoretical yeild – yeild) / theoretical yeild) x 100

                                = 0.0418 x 100

                                = 4.18 %

∴ Therefore the percent error of the strontium sulphate yeild in this experiment is 4.18 %

Table 2: Theoretical calculations of the masses and moles of the reactants and products.

SrCl2 - 6H20

        Cu(II)SO4 - 5H20

        SrSO4

        Cu(II)Cl2

        11H2O

        1.00g

        1.00g

        0.6888g

        0.5043g

        0.7431g

        266.58 g/mol

        249.62 g/mol

        183.64 g/mol

        134.45 g/mol

        18.01 g/mol

        3.751x103- mol

        4.006x103- mol

        3.751x103- mol

        3.751x103- mol

        4.126x102- mol

        

Analysis:

2. The percentage yeild in the experiment is 95.82 %, which is greater than the target yeild of 95 %.

 The following are possible factors that may contribute to acheiving a higher yeild. Firstly, it is possible that there was contamination from outside sources, such as lint or dust particles that could have fallen into the drying precipitate. Secondly are impurities accumulated through water. Non-distilled water can contain many  minerals and impurities , aswell as absorbing chemicals in the surrounding air which can skew results. According to the city of Ottawa's website, there are  many contaminants in water, the two of those being fluoride and chlorine. Fluoride is naturally present in the air and soil, and can dissolve into water. Chlorine is used by the city in the water to kill bacteria. Average tap water contains 0.7 mg/L  of fluoride and 100 ppb, or parts per billion of chlorine. These insignificant substances, in additions to those not named here, can change the way the reaction takes place. Thirdly is lingering moisture, which can be present because of thick acumulation of precipitate which causes moisture to remain at its center. Water could also be present due to outside sources, such as higher than normal humidity levels present in the laboratory or water bottle fights that may have taken place and interacted with the results.  To validate this reasoning, another student who acheived a higher yeild, Yannick Brisebois notes in his analysis that he was closely located to the water fight, similarily to this experiment. Lastly, misreaction is another way the precipitate was higher than expected. The reactants could have possibly reacted with the levels of fluorine or chlorine in the water, as covered in the example above. Since perfect reactions are impossible, it is likely that some of the reactants were not used up in the reaction, and were left in the precipitate. This would increase the mass of the precipitate because both the strontium chloride and the copper sulphate were hydrates, which have a higher molar mass than the products because of the attached waters. For example, according to table 2, the masses of the reactants strontium chloride and copper sulphate are 266.58 and 249.62 g/mol respectively, while  the precipitate, strontium sulphate only has a molar mass od 183.64. Any ammount of extra reactant would weigh down the mass of the precipitate.

3. The following steps were taken to ensure the reaction went to completion. First, the ammount of transfers were kept to a minimum in order to preserve as much of the orginal reactants as possible. Multiple transfers can cause reactants or precipitate to adhere to the walls of the beakers or the funnel. There are only two transfers present in this procedure. Second,  the solutions were dissolved into aqeous solutions to facilitate a reaction and increase the ammount of reaction taking place. Without a solution, the two substances would not have reacted in a solid state. Solutions also increase the likeliness of the most possible reaction, because of its containment, as opposed to a gas, and the potion of the particles within, unlike a solid. Both reactants were dissolved into water in order to maximise the reaction and ensure it took place. The reaction was finally stirred for a mintute to maximise the reaction. The stirring added heat and motion, which is another form of heat, which allows more reactant to react properly. The heat increases the speed at which the particles move within the liquid, which leads to more collisions, and finally more reaction taking place. Finally, the original beakers and the funnel were washed down with water and passed through the filter to ensure all possible remaining reactant had been added to the apparatus.

Refrences:

1. Nelson 11 Chemistry (2005)

2. http://ottawa.ca/en/env_water/water_sewer/water_wells/quality/facts/index.html

3. http://sargentwelch.com/pdf/msds/Strontium_Chloride_6-Hydrate_723.00.pdf

4. https://www.sciencelab.com/msds.php?msdsId=9923597