Salahaddin University – Erbil College of Science Chemistry Department
Lab Report
Inorganic Chemistry Name of experiment: i. ii.
iii.
Preparations of tetraamminecopper (II) sulfate monohydrate. Determination NH3 in the complex Cu(NH3)4]SO4.H2O). Determination Cu (II) in the complex Cu(NH3)4]SO4.H2O).
Prepared by Students: i. Kosary Yasin Ahmed ii. Omer Taha Abdulqader iii. Aram Aziz Qader
Started date 29/10/2015, ended date 5/11/2015 Supervised by Dr. Azad H Mahdy, MSc. Sardar, & MSc. Adnan
Introduction
Tetraamminecopper (II) sulfate is the inorganic compound with the formula [Cu(NH3)4(H2O)n]SO4. This dark blue solid is a metal complex with faint odor of ammonia. It is closely related to Schweizer's reagent, which is used for the production of cellulose fibers in the production of rayon. It is used to print fabrics, used as a pesticide and to make other copper compounds like copper nano-powder .
Synthesis
synthesis the coordination compound tetraamminecopper (II) sulfate m onohydrate [Cu(NH3)4]SO4•H2O. This will be accomplished by adding concentrated ammonia (NH3) to copper (II) sulfate sulf ate pentahydrate which will displace the water molecules bound in theoriginal copper complex, and a dramatic color change occurs. The reaction of ammonia with the copper(II) sulfate pentahydrate is a two-step process. In the first step, solid copper (II) hydroxide is formed which is light blue in color. The Cu(OH)2(s) dissolves as additional quantities of ammonia are added in the second step to form the dark blue [Cu(NH3)4]2+ complex.
Reaction 1:
[Cu(H2O)4]SO4•H2O NH4+(aq)
+ 2NH3
(aq)
+2
(s)
+ 2 NH4+(aq) + 2 NH3
(s)
(aq)
[Cu(NH3)4]
⎯→
The overall net equation for the reaction is
Cu(H2O)4]SO4•H2O
Cu (H2O)2(OH)2]SO4 •H2O
⎯→
Reaction 2:
Cu(H2O)2(OH)2]SO4 •H2O SO4•H2O (aq) +4 H2O (l)
(aq)
(aq)
+ 4 NH3
[Cu(NH3)4]SO4•H2O + +4 H2O
(aq) ⎯→
(l)
Chemical Reaction and Solubility
The deep blue crystalline solid tends to hydrolyse and evolve (release) ammonia upon standing in air.[1] It is fairly soluble in water. The brilliant dark blue-violet color of tetraamminecopper(II) sulfate solution is due to presence of [Cu(NH3)4]2+. Often, the dark blue-violet color is used as a positive test to verify the presence of Cu2+ in a solution.
Structure and Properties
The solid state salt of tetraammine copper (II) sulfate contains the [Cu(NH3)4H2O]2+, which has a square pyramidal molecular geometry. The bond length between the atoms in the crystal are measured using X-ray crystallography; the Cu-N and Cu-O distances dis tances are about 210 and 233 pm.[3] Cu(NH3)The correct concentrations of ammonia and copper sulfate solution can be determined by colorimetry. The combination of the correct concentrations will produce the highest absorbance read out on the colorimeter and as a result the formula of the complex can be verified.
Uses
Most pesticides contain ammonium sulfate. Tetraammine copper sulfate is often used as a starting material to make ammonium sulfate. Ammonium sulfate is used as an agricultural spray adjuvant for water-soluble insecticides, herbicides, and fungicides. There, it functions to bind iron and calcium cations that are present in both well water and plant cells. It is particularly effective as an adjuvant for 2, 4-D (amine), glyphosate, and glufosinate herbicides.[4]The brilliant dark blue-violet color and a good solubility make tetraammine copper (II) sulfate an excellent chemical to dye fabrics. Some of the recent research and development for copper include various studies of tetraaminecopper (II) sulfate. One such research is “Chemical reduction method for preparing copper nano-powder nano -powder with high purity using sodium hypophosphite as reductant”, which uses tetraaminecopper (II) sulfate.
Determination ammonia (NH3) and Copper (CU) percentage
To determine the percentage ammonia and copper in the amine-copper sulfate coordination compound, [Cu(NH3)x]SO4 * y H2O, synthesized in a previous lab period and from this deduce a value for the number of coordinated ammonia molecules x and the number of waters of hydration, y, in the molecular formula. The moles of ammonia present in a sample of the solid salt will be determined by an acid-base titration using standardized st andardized hydrochloric acid. Upon dissolution of the compound in water the ammonia ligands are displaced by water: 1) [Cu(NH3)x]SO4*yH2O + xH2O -->[Cu(H2O)x]2++xNH3+SO42-+y H2O The basic ammonia molecules are then neutralized with HCl to a methyl-orange end-point according to the 1:1 reaction: 2) x NH3 + x HCl --> x NH4+ + x ClThe moles of copper in the sample will be determined by an oxidation-reduction titration involving first reduction of Cu (II) to Cu (I) with excess iodide ion: 3) 2 Cu 2+ + 5 I- --> 2 CuI + I3The dark-brown colored triiodide ion, I3-, will then be titrated with standardized sodium thiosulfate solution according to the reaction: 4) I3- + 2 S2O3 2- --> 3 I- + S4O6 2The endpoint is to be detected using a starch solution as an indicator. By adding reactions 3) and 4) and dividing through by the common factor of two, the mole relationship between copper-present and the thiosulfate used is i s determined to be 1:1. 5) Cu2+ + I- + S2O3 2- --> CuI + 1/2 S 4O6 2To obtain the percentages of other consitituents of the solid, namely the sulfate s ulfate anion and the water content, an indirect means mea ns will be used. The % SO4 2- will be taken to be 1.51 times the average % Cu found in the sample on the assumption as sumption that for every mole of copper (2+) cation there must be a mole of sulfate (2-) anion. Finally the percent by weight of water in the sample can be taken to the difference between the sum of the percent by weights of the other three species and 100%. To deduce the chemical formula for the coordination compound containing the copper-ammonia complex cation, sulfate anion and waters of hydration, [Cu(NH3)x]SO4 * y H2O that was synthesized during a previous laboratory session.
The percent ammonia in a sample of the solid salt will be determined by an acidbase titration based on the reaction between ammonia and hydrochloric acid. x NH3 + x HCl --> x NH4Cl The percent copper in the sample will be dtermined by an oxidation-titration involving the overall reaction: Cu 2+ + I- + S2O3 2- --> CuI + 1/2 S 4O6 2The percent sulfate in the sample sampl e will be taken as 1.51 times the t he percent copper in the sample based on the th e assumption that for every copper ion in the sample there must be a sulfate anion. The factor of 1.51 comes from the ratio of the molecular weights of SO4 2- and Cu2+. The percent by weight of water in the sample can then be taken to be the difference between the sum of the t he percent by weight of the other species and 100%. Ok here is what I need after all the information. % NH3 and % Cu based upon the calculations given at the beginning.
i.
Materials Used In: Preparations of tetraamminecopper (II) sulfate monohydrate: a) Cupper sulfate (CuSO4) use for the sample b) Water (H2O) use for dissolving the sample c) Ammonium hydroxide (NH4OH) The addition of ammonia can shift the equilibrium, because The precipitate Cu(OH) 2 which is formed is not stable, so it can be dissolved again., which causes the formation of complexes [Cu (NH 3)4]SO4 according this equations: CuSO4 (aq) + NH4OH CuSO4 (aq) + 4NH3 (aq)
Cu(OH)2 (s) + (NH4)2SO4 [Cu(NH3)4]SO4 (aq)
→ →
d) Ethanol use for precipitating agent and for washing the precipitate and dissoving . ii.
Determination NH3 in the complex Cu(NH3)4]SO4.H2O): for dissociating the complex to ions. a) Hydrochloric Acid (HCl) use for dissociating for (as titrant) b) Sodium hydroxide (NaOH use for (as c) Methyl Red use for ( (as indicator for detecting the end point by changing the color )
Procedure
Preparations of tetraamminecopper (II) sulfate monohydrate:
1 gm of cupper sulfate
(CuSO4)
dissolve in
3 ml of Water H2O
then add
10 ml Ammonium hydroxide (NH4OH) n e h t
Stir the mixture for 5 min d d a t a h t r e t f A
5 ml of Ethanol
Stir for 15 min. and
cool the mixture in ice bath
Dry the ppt. in air
Wash ppt. by 2ml of ethanol
Filter the mixture
Determination NH3 percentage in the complex Cu(NH3)4]SO4.H2O):
0.1gm of complex Cu(NH3)4]SO4.H2O
dissolve in
35 ml of HCl 0 .1 M
Then titrated with
NaOH solution (o.1M) d d a n e h T
At end point change the color from pink to light orange
Methyl red as indicator
Determination Copper(И) percentage in the complex Cu(NH3)4]SO4.H2O):
0.1gm of complex Cu(NH3)4]SO4.H2O
dissolve in
20 ml of HCl 2M
Add
NH4OH (Conc.) drop wise until the color of the mixture changed to dark blue d d a n e h T
CH3COOH solution (2N) slowly until the color of the mixture changed to light greenish Blue blue d d a n e h T
Titrated I2 Liberated with standard solution of Na2S2O3 (0.1N) by using starch as indicator
Then
0.6
of KI to the solution
Result Preparations of tetraamminecopper (II) sulfate monohydrate: Weight of filter paper Weight of complex + filter paper
1.34 gm 2.0 gm
Weight of complex
0.66 gm
Percentage of yield
42.88 %
Determination NH 3 in the complex Cu(NH 3)4]SO4.H2O): Weight of NH 3 in Complex
0.0272 gm
Percentage of NH3 in Complex
27.2 %
Percentage of error
1.69 %
Determination Cu (II) in the complex Cu(NH 3)4]SO4.H2O): Weight of Cu (II) in Complex Percentage of Cu (II) in Complex Percentage of error
0.3087 gm 30.87 % - 19 %
Discussion & conclusion 1-To synthesis tetraamminecopper(II) sulphate(VI) monohydrate Cu(NH3)4]SO4.H2O. 2- To Determination NH3 in the complex complex Cu(NH3)4]SO4.H2O. 3- To Determination Cu (II) in the complex Cu(NH3)4]SO4.H2O.
During of the experiment one , the complex salt Cu(NH3)4 SO4.H2O was produced when the cupric salt is dissolved in excess ammonia. It will formed a dark blue solution due to the formation of Cu(NH3)4
2+
complex ions, Then put the solution
in ice bath for an quarter hour, This steps is important to make sure that the complex ions will form completely. The reason that we used ice bath in this experiment is to help the process of recrystallization occur a lot faster than the usual. After the filtration process The crystal of complex are formed in dark blue color precipitate of [Cu(NH3)4SO4] on filter paper and the filtrate is clear blue. In the second part of the experiment , determined of NH3 in the complex salt Cu(NH3)4 SO4.H2O by (indirect method) using titration, after dissociating the complex by (HCl) titrating with (NaOH) using the methyl red for detecting end point, at end point the color change from pink to light orange. In the third part of the experiment , we determined of Cu (II) in the complex salt Cu(NH3)4 SO4.H2O by iodometric method (indirect method) meaning we cannot direct use I2 therefore we use KI as reducing agent, KI reduced the Cu+2 to Cu+ and itself (KI) is oxidized to I2 ,thus the number of equivalent of Cu+ equal to number of equivalent I2 therefor by these way we can determine number of equivalent equival ent of Cu+2 in the complex salt Cu(NH3)4 SO4.H2O, during titration we use starch as indicator the color of the solution changed to dark brown when titrated the solution with Na2S2O3 at end point the color changed to colorless.
While in the first experiment the mass that we obtained for complex salt, Cu(NH3)4SO4 .H2O is (0.66gm), which is less than the theoretical value,(1.539 gm). Thus the yield percentage that is obtained is (42.88 %). While carrying out this experiment there might be some errors occurred that may effects the percentage of yield to be less than the theoretical value. For example not completely dissolved the sample, some of the samples remain in the flask or when we filtered the salt, we might not do it the right way. There might be a salt that is not well filtered. Besides that, loss some of the complex during transferred the precipitate during weighting it. There are also some problems when we need to take the weight of the salts. The reading of the balance was not stable maybe m aybe due to the impurities from the previous experiment that was left inside it . In the second experiment second experiment the the mass that we obtained for NH3 (0.0272 gm) which is less than the theoretical value,(0.02769 gm).Thus the error percentage that is obtained is (1.69 %), so I think this value of error returned for bad precaution special during reading the buret at end point. In the second experiment, second experiment, the practical weight of the Cu+2 equal to (0.03087 gm) which is greater than the theoretical value (0.02585 gm). Thus the error percentage that is obtained is (-19 %), so I think this value of error returned for presence of impurity in the complex salt Cu(NH3)4 SO4.H2O and bad precaution special during reading the buret at end point & many factors.
References
1. www.chemistrylabmanual.com 2. Wikipedia: i. American Elements – The material science company; tetraammine copper(II) sulfate monohydrate; CAS 10380-29-7 ii. Morosin "The Crystal Structures of Copper Tetraammine Complexes. A. Cu(NH3)4SO4.H2O and Cu(NH3)4SeO4" Acta Cryst. 1969, vol. B25, pp. 19-30. doi:10.1107/S0567740869001725 doi:10.1107/S0567740869001725 iii. Li, Yudan; Wang, Wenjie; He, Chuan.; Chemical reduction method for preparing copper nanopowder with high purity using sodium hypophosphite as reductant, Faming Zhuanli Shenqing, Dec 4, 2013, CN 103418801
