Analysis Experiment

EXPERIMENT 4 : Preparation of Double Salt and Complex Salt

OBJECTIVES: 1. Prepare complex and double salt 2. Differentiate between complex and double salt 3. Identify the bond character between complex and double salt

THEORY In this experiment, we are preparing different salt that is double salt and complex salt. For the first one, double salts salts containing containing more than one cation or anion. They form when one salt and more dissolved in a liquid then together crystallize in a regular pattern. They have their own crystal forms which need not be the same as that of either of their  compon componen entt salt salts. s. This This is a soli solid d stat statee phemn phemnom omen enon on where where in solu soluti tion on they they are are decomposed completely, or nearly so, into of their component salts. In this respect double salt are distinguished from complex salts, which give complex ions of their own in solution. Double salts are extremely numerous. Complex salt is another type of salt. It is a salt that does not dissociate in solution. When ammonia is added to a solution of a cupric salt, a light blue precipitate of cupric hydroxide is first formed which dissolves in excess of ammonia to form a deep purplish blue solution. solution. The colour is due to the complex ion Cu(NH3)4+. The sulfate of this ion is easily obtained in solid form as the hydrate Cu(NH3)4SO4. H2O.

METHODOOGY Double salt, CuSO4.(NH4)2SO4.6H2O 0.03mole of copper sulfate + 0.03mole ammonium sulfate was added into a beaker  contain 15ml of hot water  ↓ Coll filter  ↓ Dry, weight ↓ Observe

Complex salt, Cu(NH3)4SO4. H2O. 10ml [NH3] + 6ml H2O and 6.25g copper sulfate was put into a beaker  ↓ 10ml ethyl alcohol was added ↓ 1 hour  ↓ Cool ↓ Filter  ↓ Wash with 10ml alcohol + 10ml [NH3]

↓ Wash with 10ml ether  ↓ Dry in oven ↓ weight

RESULT AND CALCULATION

A) Double salt

Sample

Number of mole

Mass of theory

Mass used in

CuSO4.5H2O (NH4)2.SO4

(mole) 0.03 0.03

(g) 7.49 3.96

experiment (g) 7.49 3.69

Mass of filter paper Mass of filter paper + sample Mass of sample

1.12 g 7.89 g 6.74 g

Calculation Salt CuSO4.5H2O

No. of mole Mass of relative molecule

= 0.03 mole = [(63.546) + (32.066) + 9 (16) + 10 (1.0079)] = 249.691

Mass

= (0.03) (249.691) = 7.49 g

Salt (NH4)2.SO4

No. of mole

= 0.03 mole

Mass of relative molecule

= [2 (14.007) + 8 (1.0079) + 32.066 + 4 (15.999)] = 132.13292

Mass

= 3.96 g

Reaction equation:

CuSO4.5H2O + (NH4)2.SO4 + H2O → CuSO4.(NH4)2SO4.6H2O

The mass of sample of CuSO4.(NH4)2SO4.6H2O from this experiment

= 6.74 g

From the theory, mass of CuSO4.(NH4)2SO4.6H2O Mass = no. of mole x mass of relative molecule

Mass of relative molecule : (63.546) + 2 (32.066) + 14 (15.999) + 20 (1.0079) + 2 (14.007) = 399.836 g/mole

Mass in theory

: (0.08) (399.836) = 11.005 g

% of sample from experiment = experiment sample

x

100

Mass in theory = 6.47 g 11.005 g

x

100

= 61.24 %

% of error

= (11.005 g – 6.74 g) 11.005 g

x

100

= 38.76 %

B) Complex salt, Tetrammine Cupric Sulfate CuSO4.(NH4)2SO4.6H2O

Sample

Mass of theory

Mass used in

Volume

CuSO4.5H2O

(g) 6.24205

experiment (g) 6.25

(ml) -

 NH3

-

-

10

Mass of filter paper Mass of filter paper + sample Mass of sample

Calculation : Salt CuSO4.5H2O

1.13 g 5.13 g 4.00 g

No. of mole

: 0.025 mole

Mass of relative molecular

: [(63.546) + (32.066) + 9 (15.999) + 10 (1.0079)] = 249.682 g/mole

Mass

: (0.025) (249.682) = 6.24205 g

The equation of reaction : CuSO4.5H2O + 4NH3 → Cu(NH3)4SO4.H2O + 4H2O

From theory, mass of Cu(NH3)4SO4.H2O = no. of mole x mass of relative molecule

Mass of relative molecule

= 63.546 + 4 (14.007) + 32.066 + 5 (15.999) + 14 (1.0079) = 245.7456 g/mole

Mass from theory

= 0.025 x 245.7456 = 6.14364 g

% of sample from experiment = mass from experiment Mass from theory =

4.00 x 6.14364 = 65.108 %

100

% errors

: (6.14364 - 4.00) 6.14364 = 34.892 %

Observation :

x

x 100

100

Observation Homogeneous Appearances

Double salt Homogeneous Sky blue

Complex salt Heterogeneous Deep blue

- colour, crystal size Behaviour in solution

Diamond shape Dissolve

Rod shape Cannot dissolve

DISCUSSION Preparation of CuSO4.(NH4)2SO4.6H2O and Cu(NH3)4SO4.H2O show the difference in constitution of structure and behaviour in solution b etween double salt and complex salt.

From the experiment, we found out that double salt can dissolve in water. Double salt  produce a homogeneous solution. The appearance are diamond shape. Formation of Cu2+ make the solution colour are sky blue.

From the experiment, double salt is CuSO4.(NH4)2SO4.6H2O. The formation of crystal is observed in sky blue colour and has a shining and coarse surface. Do not stir during the cooling process to get the right result. The salt is highly soluble to form homogeneous solution. 6.74 g salt mass formed while the theory value is 9.9959 g. The percentage error  is 38.76%

Equation reaction: CuSO4.5H2O + (NH4)2SO4 → CuSO4.(NH4)2SO4.6H2O The mass of double salt that we get is very little compare to the theory value. This might  be happen because of not all the crystal is fully transferred into the filter paper by using Buchner funnel. There might have many errors occur in the electrical balance that make the reading not precise. The filtering process is not perfect and caused some crystal lose.

The complex salt is Cu(NH3)4SO4.H2O. The colour of the crystal formed is deep blue. The structure are weak and not shining. Complex salt cannot dissolve in water. The formation of Cu(NH4)44+ turn the solution into deep blue colour. It is more concentrated and easy to formed Cu(NH4)4+4 complex ion by leaving the solution for 1 hour. To get the best result the solution must be cooling in natural. The shape of crystal is small and tiny like rod. Mass of complex salt is 4.00g while the theory is 6.14364g. the percentage error is 34.892%

The reaction is : CuSO4.5H2O + 4NH3 → CuSO4.(NH4)2SO4.H2O + 4H2O

The result that we get from experiment and theory are different due to some errors which are, the cooling process is not complete, the error in the electrical balance during take the weight value, some salt is still leaving on the glass when prepare the salt, the crystal lost from the imperfect filtering process and only some the crystal is transfer into the filtering  paper by using Buchner funnel.

PRECAUTION 1. Weight CuSO4.5H2O and (NH4)2.SO4 approximately. 2. Do the mixture in fume cupboard. 3. Do the cooling process slowly and complete.

CONCLUSION 1. From this experiment we got the mass of double salt is 6.47 g while mass of  complex salt is 4.00g. 2. The double salt characteristics are homogenus, dissolve and its appearance is sky  blue and diamond shape. 3. The complex salt characteristics are heterogenus, cannot dissolve and its appearance is deep blue and rod shape.

REFERENCES :

1. Shriver & Atkins , Oxford Inorganic chemistry, fourth edition 2. www.tutornext.com/difference-between-double-salt-complex/2461 3.

www.britannica.com/eb/topic-129980/complex-ion

QUESTIONS

1. Name three double salts that are important in industry or in laboratory practice.

•

Potassium sodium tartrate-in the process of silvering mirror, an ingredient of Fehling’s solution.

•

Calcium double salt - additive in food product (such as French Fries and  potato chips)

•

Alum - purify water and harden plaster of Paris.

2. Metallic cations form complex ions with ammonia. •

•

•

Cadmium, nickel argentum.

3. When the complex salt is dissolved in water, a slight precipitate appears. What is this precipitate, and why is it formed? Cu(OH)2, because Cu is bind to water molecule.

4. What is the difference in constitution between tetrammine cupric sulfate and cupric ammonium sulfate?