Lab report 6 copper and nickel sample report PDF

Preview

Summary

LAb report...

Description

Falcone 1

Copper and Nickel Coordination Compounds and Analysis of a Nickel Ethylenediamine Complex A Laboratory Report for CHEM 2145 Performed by: Kayla Falcone Performed: 24 October, 31 October, and 7 November 2013 Date Submitted: 21 November, 2013

Abstract: Coordination compounds contain metals that form ionic and covalent bonds with ligands. Two copper coordination compounds, CuSO4 and [Cu(NH3)4]SO4•H2O, were formed by either the addition of heat or ammonia. After the new solids were formed, the percent yield of CuSO4 was 101.4% and the percent yield for [Cu(NH3)4]SO4•H2O was 82.3%. When ammonia and ethylenediamine were added to the nickel coordination compound, [Ni(H2O)6]Cl2, the nickel atoms formed coordinate covalent bonds with water, ammonia, and ethylenediamine. When the color changed from green to lavender after the addition of ammonia, [Ni(NH3)6]Cl2 was formed with a percent yield of 85.2%. When ethylenediamine was added, violet [Ni(en)3]Cl2 was formed with a percent yield of 81.2%. The amount of nickel and en in [Ni(en)3]Cl2 was determined by measuring the absorbance of three samples with a spectrophotometer, and a titration with HCl. The average value of moles of Ni2+ per gram sample was 2.5x10-3 moles, and the average percent weight was 14.4%. The average value of moles of en per gram sample was 9.04x10-3 moles, and the average percent weight was 54.4 %. These value do not compare to the theoretical values, so the [Ni(en)3]Cl2 sample was not pure because there was not a 3:1 ratio.

Falcone 2

Introduction: The goal of the three experiments was to react and synthesize compounds that contained metal ions that were combined with one or more ligands, and analyze the nickel ethylenediamene complex. These compounds contain complex ions, and the compounds that contain complex ions are known as coordination compounds. Coordination compounds contain metals that can form ionic and coordinate covalent bonds (Jespersen, 2012). One example of this type of compound is CuSO4•5H2O because it has four water molecules that are connected by a coordinate covalent bond to copper, and one water molecule that is in the solid structure with the sulfate ion. Once the compound is heated, the water will evaporate and white anhydrous copper sulfate will form. With the addition of ammonia molecules, the water molecules will be replaced, and the Cu2+ ion will be hydrated to create [Cu(H2O)4]2+ complex. The new compound, [Cu(NH3)4]SO4•H2O, will be formed by this reaction(Barlatt, Hallock-Waters, Paul, Richard, 2013-2014). The equation is CuSO4 + H2O + 4NH3→ [Cu(NH3)4]SO4•H2O A second example of a coordinate compound is [Ni(H2O)6]Cl2. The nickel atoms formed coordinate covalent bonds with water and ammonia to create a lavender nickel coordination compound, [Ni(NH3)6]Cl2. When a bidentate ligand, ethylenediamine, was added, the Lewis base attached itself to the metal ion thus creating a violet [Ni(en)3]Cl2 (Barlatt, Hallock-Waters, Paul, Richard, 2013-2014). The equation for this reaction is NiCl2•6H2O + 3en→ [Ni(en)3]Cl2 + 6H2O These molecules or ions other than water, called ligands, are Lewis bases which will bond directly to the metal ion, Cu2+ or Ni2+, producing a change in the electronic energy levels of the metal ion (Jespersen, 2012). The energy of light absorbed by the electrons in the metal ion will

Falcone 3

change, and the formed compound has a new color. A spectrophotometer can be used to determine the molar concentration of nickel in the [Ni(en)3]Cl2 solution by measuring the absorption of light and wavelength produced (Barlatt, Hallock-Waters, Paul, Richard, 2013-2014). The spectrophotometer can also be used to calculate the concentration of certain ions in a solution. Beer’s Law helped to describe the relationship between the concentration of the sample and the absorption of light. The equation can be written as A=ԑbc. A represents the absorbance of the sample, ԑ is the molar absorptivity (7.4 L mol-1 cm1), c is the molar concentration of the absorbing ion in the solution, and b is the length of the path taken (Barlatt, Hallock-Waters, Paul, Richard, 2013-2014). The amount of moles of en in [Ni(en)3]Cl2 can be determined by the titration with HCl. The process will determine how many moles of the product are being released in a liter. By knowing how many liters it took for the titrant to turn from blue to pale yellow, the actual molar concentration of the product can be calculated. This concentration will represent how many moles of the product there were in each liter of the solution. Experimental: During the synthesis of CuSO4•5H2O, and [Cu(NH3)4]SO4•H2O, a few procedures were followed to form these compounds. About five grams of blue copper (II) sulfate pentahydrate was weighed and placed into an evaporating dish. The solid was heated gently on a hotplate and stirred until the color turned from blue to white. The white product, CuSO4, was then cooled and weighed. All of the CuSO4 was then placed into a 50 mL beaker, and 15 mL of water were added. The solution was heated gently on the hotplate until the solid was dissolved and then cooled to room temperature. Concentrated ammonia was added a few millimeters at a time until the solution was a dark blue. Ten mL of methanol in a test tube were placed into an ice

Falcone 4

bath, so it could become cold. The entire methanol was mixed with the solution, and a precipitate formed. An ice bath was used to cool the system and help the precipitate form. A Buchner funnel and suction flask was used to filter the solid, and it was washed with cold methanol. The solid was dried by vacuum filtration and pressed it in between two filter papers. The product, [Cu(NH3)4]SO4•H2O, was placed into a clean vial and weighed. The next part of the experiment started with solid [Ni(H2O)6]Cl2, and it was transformed into two other nickel coordination compounds, [Ni(NH3)6]Cl2 and [Ni(en)3]Cl2. The process of synthesizing [Ni(NH3)6]Cl2 started by 4g of NiCl2•6H2O were weighed and dissolved in 10 mL of water in a 150 mLbeaker. Ten mL of concentrated ammonia were slowly added to the beaker, and the solution was cooled in an ice-water bath. Then, 20 mL of cold 95% ethanol were added, and a lavender precipitate began to form. The solution was cooled again in the ice bath until the mixture was settled. The mixture was vacuum filtered by a Buchner funnel and washed with portions of cold 95% ethanol. The dry product, [Ni(NH3)6]Cl2, was weighed in a clean vial. The coordination compound, [Ni(en)3]Cl2, was prepared by weighing out 4g of NiCl2•6H2O, and the solid was dissolved in 10 mL of water in a 150 mL beaker. The solution was cooled in an icewater bath, and 5 mL of ethylenediamine were carefully added. The mixture was placed in the ice bath again, and 15 mL of cold 95% ethanol were added. The mixture was cooled until it became slushy, and there was a violet precipitate. The solid was vacuum filtered with the Buchner funnel and washed with 95% ethanol. Once dry, the product [Ni(en)3]Cl2, was placed into a clean vial and weighed. Spectrophotometers and a titration with HCl were used to determine the amount of nickel and ethylenediamine that was in the [Ni(en)3]Cl2 product. Three samples of solid [Ni(en)3]Cl2 were dissolved in water and diluted to make three different samples used to compare the

Falcone 5

concentration and absorption. About 0.3g, 0.4g, and 0.5 g of solid [Ni(en)3]Cl2 were placed in three different beakers, and each solid was dissolved in 20 mL of distilled water. Then 10 mL of 25% ethylenediamine solution were added to each. The three solutions were placed in separate 100 mL flasks and each was filled with distilled water to the 100 mL mark. The solutions were capped and the flask was inverted. A spectrophotometer was connected to a laptop, and an absorbance was recorded for each diluted solution.The absorbance was recorded three times for each diluted solution with the maximum wavelength at 540 nm. A titration with HCl was performed to determine the number of moles of en in each three samples of [Ni(en)3]Cl2. The three samples consisted of about 0.15 g of [Ni(en)3]Cl2 and each was dissolved in 10 mL of distilled water in an Erlenmeyer flask. Four drops of bromocresol green indicator were added to each flask, and each sample was titrated with HCl. The reaction was complete when the solution turned from blue to a pale yellow (Barlatt, Hallock-Waters, Paul, Richard, 2013-2014). Results and Discussion: The final mass of each copper and nickel coordination compound formed was used to calculate the percent yield of each compound. The table below shows each coordination compound’s calculated percent yield from the experimental mass divided by the actual mass. Table 1. Percent yields for copper and nickel coordination compounds CuSO4 3.242

[Cu(NH3)4]SO4•H2O 4.050

[Ni(NH3)6]Cl2 3.365

[Ni(en)3]Cl2 4.249

Experimental mass (g) Theoretical 3.196 4.924 3.920 5.235 mass (g) Percent yield 101.4 82.30 85.20 81.17 (%) All calculations for the theoretical mass and percent yield can be seen in the appendix. The

percent yield was greater than 100% for the CuSO4 compound because there was excess water in

Falcone 6

the solid. The solid, CuSO4•5H2O, was heated very gently because if it was dehydrated too much then product would have been lost and the yield would have been significantly less than 100%. The percent yield was less than 100% for the [Cu(NH3)4]SO4•H2O compound because some product was lost during the transfer of the solid from the beaker to the Buchner funnel. The ligand present during this reaction was water which was also the Lewis base that attached to the Lewis acid, CuSO4, and that is the reason why water dissolved the solid. The percent yield of the nickel coordinate compounds, [Ni(NH3)6]Cl2 (85.2%) and [Ni(en)3]Cl2 (81.2%) were also less than 100%. During the transfer of the solid product into the vial for both compounds was difficult and some solid was lost during the process. Another reason for the percent yield being less than 100% could be that the reaction of when the precipitate was forming was disturbed too soon. The solid was not completely formed before it was filtered. The 95% ethanol was used to wash the solid rather than water because it would not dissolve the solid. Water was used to dissolve each nickel compound and the ammonia and ethylenediamine were replacing the water molecules. The following figures are the two nickel coordinate compound structures formed during this experiment. Figure 1. Structure of [Ni(NH3)6]Cl2

Figure 2. Structure of [Ni(en)3]Cl2

Falcone 7

[Ni(NH3)6]Cl2 was a lavender color because the concentrated ammonia solution that was added created the hexamminenickel (II) chloride, and [Ni(en)3]Cl2 was a violet because ethylenediamine was added rather than ammonia. The green original color of the compound came from nickel, but it turned lavender and violet after the addition of ions other than water to bond to the metal ion to form a complex. [Ni(en)3]Cl2 would be more stable because its coordination number is greater than [Ni(NH3)6]Cl2. The ethylenediamine was a bidentate ligand which meant both nitrogen atoms bonded with the nickel ion. The average value for the moles of Ni per gram and average weight percent of Ni was calculated by calculating the concentration of Ni by measuring the absorbance of each diluted solution of [Ni(en)3]Cl2. The tables below show the three absorbance measurements for three different diluted samples of [Ni(en)3]Cl2 at a maximum wavelength of 540 nm. It also demonstrated the values that led to the calculation of moles of Ni per gram and weight percentage of Ni.

Table 2. Absorbance of [Ni(en)3]Cl2 with mass of 0.312 g

Falcone 8

Sample mass (g) Absorbance [Ni2+] Moles of Ni2+(g) Mass of Ni2+(mol) Moles of Ni2+ per gram (mol) Weight percent Ni2+ (%) Average moles of Ni2+ per gram (mol) Average weight percent Ni2+(%)

Sample 1 0.312 0.057 7.7x10-3 7.7x10-4 0.045 2.5x10-3

Sample 2 0.312 0.057 7.7x10-3 7.7x10-4 0.045 2.5x10-3

Sample 3 0.312 0.053 7.2x10-3 7.2x10-4 0.042 2.3x10-3

14.4

14.4

13.5

2.4x10-3 14.1

Table 3. Absorabnce of [Ni(en)3]Cl2 with mass of 0.401 g

Sample mass (g) Absorbance [Ni2+] Moles of Ni2+(g) Mass of Ni2+(mol) Moles of Ni2+ per gram (mol) Weight percent Ni2+ (%) Average moles of Ni2+ per gram (mol) Average weight percent Ni2+(%)

Sample 1 0.401 0.072 9.7x10-3 9.7x10-4 0.057 2.4x10-3

Sample 2 0.401 0.073 9.9x10-3 9.9x10-4 0.058 2.5x10-3

Sample 3 0.401 0.073 9.9x10-3 9.9x10-4 0.058 2.5x10-3

14.1

14.5

14.5

2.5x10-3

Table 4. Absorbance of [Ni(en)3]Cl2 with mass of 0.510 g

14.4

Falcone 9

Sample 1 0.510 0.092 0.012 1.2x10-3 0.070 2.4x10-3

Sample 2 0.510 0.094 0.013 1.3x10-3 0.076 2.5x10-3

Sample 3 0.510 0.094 0.013 1.3x10-3 0.076 2.5x10-3

Sample mass (g) Absorbance [Ni2+] Moles of Ni2+(g) Mass of Ni2+(mol) Moles of Ni2+ per gram (mol) 13.8 15.0 15.0 Weight percent Ni2+ (%) 2.5x10-3 Average moles of Ni2+ per gram (mol) 14.6 Average weight percent Ni2+(%) As the mass of the sample of [Ni(en)3]Cl2 increased, the absorbance, average moles of Ni per gram, and average weight percent also increased. Since there was a greater amount of Ni2+ in the least diluted solution, there were more covalent bonds being formed which produced a greater absorbance. This would also explain why the moles of Ni2+ per gram increased because there was more nickel available. The average amount of moles of Ni2+ per gram for each sample was 2.46x10-3 moles, and the average weight percent was 14.4%. All the calculations can be seen in the appendix. The theoretical value of the weight percent was 18.9%, and the theoretical value of moles of nickel per gram sample was 3.24x10-3 mol. The percent error was 24% for the average moles of nickel per gram sample. The different concentrations of nickel for each sample were different, so this could account for this error. The number of moles of en in three samples of [Ni(en)3]Cl2 was calculated by a titration with 0.1482 M HCl. The mass of en and weight percent of en was calculated by finding the amount of moles of en in each sample. The following table demonstrates how the average value for the moles of en per gram and weight percent of en was calculated from the titration with HCl. Table 5. Titration of [Ni(en)3]Cl2 with standardized HCl

Falcone 10

Sample 1 0.144 15.35

Sample 2 0.151 17.10

Sample 3 0.145 30.00

Mass (g) Initial buret reading (mL) Final buret reading 34.25 34.10 47.73 (mL) Volume HCl (mL) 18.90 17.00 17.73 Moles of HCl (mol) 2.801x10-3 2.519x10-3 2.628x10-3 Moles of en (mol) 1.401x10-3 1.260x10-3 1.314x10-3 Mass en (g) 0.0842 0.0757 0.0790 -3 -3 -3 9.73x10 8.34x10 9.06x10 Moles en per gram sample (mol) Weight percent en (%) 58.5 50.1 54.5 -3 Average Moles en per 9.04x10 gram sample (mol) Average weight 54.4 percent en (%) The average moles of en per gram sample was 9.04x10-3 moles and the average weight percent en was 54.4%. The theoretical weight percent of en was 19.4%, and the theoretical value for the amount of moles of en per gram sample was 9.6x10-3 moles. The percent error for this value was 5.8%. This value can be accepted by the calculated weight percent was not close to the theoretical value. The reason for this was a poor titration with HCl. Too much HCl was released into the solution thus lowering the amount of en in the solution. The calculated weight percent for nickel (14.6%) and en (54.4%) are not close to the theoretical value of nickel (18.9%) and en (19.4%). These differences show that the compound was not pure because there was not a 3:1 ratio of en to nickel.

Conclusion: During the process of creating two new copper coordinate compounds from CuSO4•5H2O, the addition of heat made the water molecules evaporate and white CuSO4 was

Falcone 11

formed with a percent yield of 101.4%. With the addition of heat, the Cu2+ ion was hydrated to form blue [Cu(H2O4]2+ with a percent yield of 82.3%. When the new nickel coordinate compound, [Ni(NH3)6]Cl2, was formed after the addition of ammonia to [Ni(H2O)6]Cl2, the color changed from a green to lavender due to new covalent bonds forming with the ammonia ions with a percent yield of 85.2%. When ethylenediamine was mixed with [Ni(H2O)6]Cl2, the nickel atoms formed coordinate covalent bonds with the water and ethylenediamine to form a violet [Ni(en)3]Cl2 with a percent yield of 81.2%. A color change was seen in each experiment due to the ligands bonded with the metal ions thus creating more electrical energy. After the [Ni(en)3]Cl2 sample prepared was evaluated by the use of a spectrophotometer to determine how the concentration of nickel was relatable to the absorbance. From these values the average amount of moles of Ni2+ per gram of sample was determined to be 2.5x10-3 moles, and the average percent weight was 14.4%. The average amount of moles of en per gram of sample was determined after the sample was titrated with a volume of HCl, and the color of the solution changed from a blue to pale yellow. The average value of moles of en per gram sample was 9.04x10-3 moles, and the average percent weight was 54.4 %. These value do not compare to the theoretical values, so the [Ni(en)3]Cl2 sample was not pure because there was not a 3:1 ratio....