Experiment 5 (full report) PDF

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SYNTHESIS AND STOICHIOMETRIC ANALYSIS OF HEXAAMMINENICKEL(II)CHLORIDE Abstract In this experiment, we synthesize complex salt hexaamminenickel (II) chloride via crystallization and purification methods. We also add a known excess quantity of an acid to neutralize the ammonia hydroxide. This is to obtain the amount of ammonia present in the product. We start the experiment by adding the green solution which is the nickel (II) chloride with the concentrated ammonia. Then, the solution turns into purple colour. Based on the calculations, average amount of N H 3 found in the product is 33.67% while for chloride ions is 19.84%.

1.0 Introduction ¿ ( N H 3 )6 ] Cl2 , is a coordination compound whose ¿ nickel atom and six ammonia molecules constitute the cation ; the anion is the chloride ion. In 2+¿ aqueous solution nickel ion ( ; Ni(II)) is surrounded by six water molecules which are N i¿ actually bonded to the central metal ion. This complex is called the hexaquanickel(II) ion. When aqueous nickel chloride is precipitated from solution, the nickel ions carry their six water molecules into the crystals and so solid nickel(II) chloride is hydrated, has the formula [ ¿(H 2 O)6 ¿ Cl2 , and is more properly called hexaquanickel(II) chloride. If ammonia is added to a solution of this salt, ammonia molecules compete with the water in bonding Ni 2+ and, because the ammonia forms a stronger bond than water, the ammonia replaces the water according to: Hexaamminenickel (II) chloride,

[ ¿(H 2 O)6 ¿ Cl2

(aq) + 6 NH 3 (aq)

→

¿ ( N H 3)6 ] Cl2 (aq) + ¿

6 H 2 O (l)

Objective of this experiment is to synthesis a complex which is complex salt hexaamminenickel (II) chloride via crystallization and purification methods. Other than that, to quantify chemical component in a chemical complex via back titration method.

2.0 Experimental 2.1 Materials Nickel(II)chloride, distilled water, concentrated ammonia, ethanol, acetone, standard hydrochloric acid, bromocresol green, standard sodium hydroxide, bromophenol blue indicator, nitric acid, diphenycarbazone, 2-propanol, standard mercury(II) nitrate solution were used in this experiment. 2.2 Synthesis of hexaamminenickel(II) chloride Nickel (II) chloride (4.413g , 0.030 mol) was dissolved in 6ml distilled water. In the fume cupboard, 12ml concentrated ammonia was added to the above solution and the mixture was warmed for about 10 minutes. The solution was cooled in an ice-bath, and 6ml ethanol was added while stirring the solution with glass rod. The formation of solid was noted. When all of the solid has formed, the solution was filtered under suction and washed with ethanol , followed by acetone. The weight of solid was recorded. 2.3 Analysis of ammonia Hexaamminenickel(II) chloride ( 0.206g , 0.894 mmol ) was weighed and dissolved by adding standard hydrochloric acid (25.0 ml, 0.28 M). 3-5 drops of bromocresol green was added to the solution. The solution was titrated with standard sodium hydroxide solution until the colour of the indicator changed to pale blue. 2.4 Analysis for chloride ion Hexaamminenickel(II) chloride (0.209g , 0.894 mmol ) was weighed and dissolved in 10ml distilled water. 2 drops of bromophenol blue indicator was added to the solution and nitric acid (1M) was added using dropper until the color of the solution changes to green. 5 drops of diphenycarbazone and 25 ml of 2-propanol was added to the mixture. The mixture was titrated with standard mercury (II) nitrate solution until the colour of the indicator changed to pale purple.

3.0 Results and Discussion Table 1 : Weight of hexaamminenickel(II) chloride Weight/(g) ¿ ( N H 3 )6 ] Cl2 + plastic ¿ Plastic ¿ ( N H 3 )6 ] Cl 2 ¿

1 1.6880

2 1.3454

0.9963 0.6717

0.9655 0.3799

Green hydrated nickel (II) chloride [ ¿(H 2 O)6 ¿ Cl2 was dissolved in water. When adding concentrated ammonia, the solution turns purple colour. Violet crystals formed in the pale navy blue solution, which was cooled in an ice bath. Then, violet crystals were filtered under suction. The procedure to synthesis hexaamminenickel(II) chloride was repeated twice because the solid of hexaamminenickel(II) chloride obtained is insufficient to proceed for −¿ analysis N H 3 and Cl ¿ .The data in table 2 show the average amount of NH 3 in the product is 33.67% which a bit far from the theoretical value which is 44.42%. The theoretical value is calculated by dividing the molar mass of 6 mole of N H 3 with molar mass of ¿ ( N H 3 )6 ] Cl2 . ¿ Table 2 : Analysis for

NH3

¿ ( N H 3)6 ] Cl2 /g ¿ Molarity of HCl Initial volume of HCl , V initial /ml Molarity of NaOH Final burette reading/ml Initial burette reading/ml Volume of NaOH /ml ¿ Volume of excess HCl , V excess /ml Volume of reacted HCl , V reacted /ml Moles of NH 3 # Weight of NH 3 ¿( N H 3) ¿ % NH 3 in ] Cl2 ¿ ¿

Weight of

0.2056

0.2181 0.2803 M

25.00

25.00 0.1009 M

36.71 7.13 29.58 10.65

30.34 3.98 26.36 9.45

14.35

15.55

0.004 mol 0.0685g 33.32

0.004 mol 0.0742g 34.02

* V (HCl, excess)=M ( NaOH) V ( NaOH ) ¿ M ( HCl) # moles of ammonia = moles of HCl = Theoritical value of % NH 3 in

mass of

%

M (HCl) V ( HCl)reacted /1000

¿ ( N H 3) ¿ ] Cl2 =(molar mass of 6 mole of NH 3 ¿ ¿

/ molar

¿ ( N H 3) ¿ ] Cl2 ) × 100 % ¿ ¿

NH 3

¿ ( N H 3) ¿ ] Cl2 =(weight of ¿¿ ¿

NH 3

¿ ( N H 3) ¿ / weight of ] Cl2 ) × 100 ¿ ¿

−¿ In table 3, the chloride analysis show that average amount of Cl ¿ in the product is 19.84%. This value was obtained when the chloride ions is titrated with standard mercury(II) nitrate.

Table 3 : Analysis for Weight of Cl2 /g

−¿ ¿ Cl ion

¿ ( N H 3)6 ]

2+¿ H g¿ Final burette reading /ml Initial burette reading /ml 2+¿ Volume of /ml H g¿ Moles of Cl−¿ −¿ Weight of Cl ¿ −¿ % Cl ¿ in ¿ ( N H 3 )6 ] Cl2

0.1617

0.2093 0.0569 M

Molarity of

12.44 3.35 9.09

21.71 12.89 8.82

0.001 mol 0.03667

0.001 mol 0.03558

22.68

16.99

2+¿ −¿¿ Cl = 2 moles of Hg¿ =

*moles of

%

−¿ ¿ Cl in

2+¿ H g¿ ¿ 2+¿ / 1000 ¿ Hg ¿ ¿ 2M¿

¿ ( N H 3 )6 ] Cl2 = (weight of

¿ ( N H 3 )6 ] Cl2 ) × 100%

¿ ( N H 3 ) 6 ] Cl2 is

The equation for the formation of NiCl2 ( aq )+ 6 NH 3 ( g )→

−¿ ¿ Cl / weight of

¿ ( N H 3)6 ] Cl2 ( aq )

NiCl2 ( aq )+6 NH 3 OH (aq ) → ¿ ( N H 3 )6 ] Cl2 ( aq ) +6 H 2 O (l) n¿CL = 2

4.413 g =0.03405 mole 129.5994 g/mol

n N H OH = 3

12 ml ×14.5 M =0.174 mole 1000

0.03 mole ×6=0.18 mole of NH 3 OH is needed when all amount of

NiCl2

is used

¿ ( N H 3) ¿ ] Cl2 . Ammonium hydroxide, for the synthesis of hexaamminenickel(II) chloride, ¿ ¿ NH 3 OH is the limiting reactant in the reaction because of insufficient amount ammonium hydroxide to react with all of the NiCl2 . To find theoretical yield of hexaamminenickel(II) chloride : ¿ ( N H 3) 0.174 mole [¿ ¿ 6] Cl2= =0.029 mol 6 n¿

Theoretical yield : 0.029 mol Actual yield : 0.6717g

× 230.032 g/mol = 6.67g

Percentage yield = =

% Ni =

actual yield × 100 % theoretical yield 0.6717 g ×100 %=10.07 % 6.67 g

¿ ( N H3) 58.693 molar mass of [¿¿ 6] Cl 2= ×100 %=25.51 % 230.032 molar mass of ∋ ¿ ¿ ¿

¿( N H 3 ) ¿ Average mass of ] Cl2 is 0.199 g ¿ ¿ ¿( N H 3) ¿ Mass of Ni in ] Cl2 = ¿ ¿

25.51 100

×0.199 g=0.0508 g

Empirical formula :

Mass Mol Ratio

2+¿ ¿¿ 0.0508g 0.0008 mol 0.0008 =1 0.0008

NH 3

0.07135g 0.004 mol 0.004 =5 0.0008

−¿¿ Cl 0.036125g 0.001 mol 0.001 =1 0.0008

The empirical formula obtained by the calculation is different from the theoretical ¿( N H 3 ) ¿ formula which is ] Cl2 . This error occurs because of a few error happens when ¿ ¿ conducting the experiment. One of them is we overshoot the end point of the titration and we also need to repeat the procedure of synthesis of hexaamminenickel(II) chloride because we did not get enough hexaamminenickel(II) chloride to proceed with procedure to analysis the ammonia and chloride ions.

4.0 Conclusion In conclusion , hexaamminenickel(II) chloride is successfully synthesis via crystallization and purification methods. The average amount of ammonia, Ni and chloride ions present in the product are is 33.67% , 25.51% , 19.84%.

References 1. Rose, N. J., Elder, M. S., & Busch, D. H. (1967). Complexes derived from the reaction of hexaamminenickel (II) ion with acetone. Inorganic Chemistry, 6(10), 1924-1926. 2. Wieder, G. M. (1986). Preparation and spectrophotometric analysis of hexaaminenickel(II) chloride: A general chemistry experiment. Journal of Chemical Education, 63(11), 988. doi: 10.1021/ed063p988’ 3. Wells, A. F. Structural Inorganic Chemistry, Oxford Press, Oxford, United Kingdom, 1984. 4. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22....