Salahaddin University – Erbil

College of Science

Chemistry Department

Lab Report

Inorganic Chemistry

Name of experiment:

i. Preparations of tetraamminecopper (II) sulfate monohydrate.

ii. Determination NH3 in the complex Cu(NH3)4]SO4.H2O).

iii. 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 monohydrate

[Cu(NH3)4]SO4•H2O. This will be accomplished by adding concentrated ammonia

(NH3) to copper (II) sulfate 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 (aq) + 2NH3 (aq) ⎯→ Cu (H2O)2(OH)2]SO4 •H2O (s) +2

NH4+

(aq)

Reaction 2:

Cu(H2O)2(OH)2]SO4 •H2O (s)+ 2 NH4+

(aq) + 2 NH3 (aq) ⎯→ [Cu(NH3)4]

SO4•H2O (aq) +4 H2O (l)

The overall net equation for the reaction is

Cu(H2O)4]SO4•H2O (aq) + 4 NH3 (aq) ⎯→ [Cu(NH3)4]SO4•H2O + +4 H2O (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 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 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 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 Cl-

The 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 + I3-

The 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 2-

The 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 determined to be

1:1.

5) Cu2+

+ I- + S2O3

2- --> CuI + 1/2 S4O6

2-

To obtain the percentages of other consitituents of the solid, namely the sulfate

anion and the water content, an indirect means will be used. The % SO4 2- will be

taken to be 1.51 times the average % Cu found in the sample on the assumption

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 acid-

base 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 S4O6

2-

The percent sulfate in the sample will be taken as 1.51 times the percent copper

in the sample based on the 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 Cu

2+. The percent by weight of water in the

sample can then be taken to be the difference between the sum of the 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.

Materials Used In:

i. 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 (NH3)4]SO4 according this equations:

CuSO4 (aq) + NH4OH → Cu(OH)2 (s) + (NH4)2SO4

CuSO4 (aq) + 4NH3 (aq) → [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): a) Hydrochloric Acid (HCl) use for dissociating the complex to ions.

b) Sodium hydroxide (NaOH use for (as titrant)

c) Methyl Red use for (as indicator for detecting the end point by changing the color)

dissolve in then add

then

A

fter that add

Procedure

Preparations of tetraamminecopper (II) sulfate monohydrate:

1 gm of cupper sulfate

(CuSO4)

3 ml of Water

(H2O)

10 ml

Ammonium hydroxide

(NH4OH)

Stir the mixture for 5 min

5 ml of Ethanol

Stir for 15 min. and

cool the mixture in ice

bath

Filter the mixture Wash ppt. by 2ml of

ethanol

Dry the ppt. in

air

dissolve in Then titrated with

Then add

dissolve in Add

Then add

Then add

Then

Determination NH3 percentage in the complex Cu(NH3)4]SO4.H2O):

Determination Copper(И) percentage in the complex Cu(NH3)4]SO4.H2O):

0.1gm of complex

Cu(NH3)4]SO4.H2O

35 ml of HCl

(0.1M)

NaOH solution

(o.1M)

Methyl red as

indicator

At end point change the

color from pink to light

orange

0.1gm of complex

Cu(NH3)4]SO4.H2O

20 ml of HCl

(2M)

NH4OH (Conc.) drop wise

until the color of the mixture

changed to dark blue

CH3COOH solution (2N) slowly

until the color of the mixture changed

to light greenish Blue blue

0.6 g of KI to the solution

Titrated I2 Liberated with standard

solution of Na2S2O3 (0.1N) by

using starch as indicator

Result

Preparations of tetraamminecopper (II) sulfate monohydrate:

Weight of filter paper 1.34 gm

Weight of complex + filter paper 2.0 gm

Weight of complex 0.66 gm

Percentage of yield 42.88 %

Determination NH3 in the complex Cu(NH3)4]SO4.H2O):

Weight of NH3 in Complex 0.0272 gm

Percentage of NH3 in Complex 27.2 %

Percentage of error 1.69 %

Determination Cu (II) in the complex Cu(NH3)4]SO4.H2O):

Weight of Cu (II) in Complex 0.3087 gm

Percentage of Cu (II) in Complex 30.87 %

Percentage of error - 19 %

Discussion & conclusion

1-To synthesis tetraamminecopper(II) sulphate(VI) monohydrate

Cu(NH3)4]SO4.H2O.

2 - To Determination NH3 in the 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 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 due to the

impurities from the previous experiment that was left inside it.

In the second experiment 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, 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

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