In this experiment, we are required to find the composing of complex ion by uninterrupted fluctuation method. Complex ions refer to a metal cation bonded to either one or more than one molecules. It is a stepwise procedure to bring forth the complex ion because every procedure has its ain equilibrium invariable ( Gretchen E. Potts,2001 ) . However, uninterrupted fluctuation method involves the continue changing of the different concentration of the solution.
Besides that, spectrophotometric method can be used to quantitatively place the unknown composing or concentration of a sample solution with comparison to a sample with known concentration. Then, spectrophotometer refers to an instrument which we can utilize it to mensurate the light strength. As we know, most of the UV-Vis spectrophotometers have a scope of the wavelength between 190nm-1100nm. This scope lies between UV and Visible light part. ( Frans F,2004 )
Figure 1: UV-visible spectrophotometer working mechanisms
In this instrument, it has 2 visible radiation beginnings. D2 and W lamp are used for UV and Visible light severally. It will guarantee that merely monochromatic visible radiation will flux through the slit. Reference cuvette is used as a space. At the terminal we can acquire the reading from the sensor.
Furthermore, Beer – Lambert jurisprudence provinces that when a monochromatic radiation base on ballss through a crystalline solution, the strength of the captive radiation is straight relative to the concentration ( degree Celsius ) and the optical pathlength, ( cubic decimeter ) of the solution. So, Absorbance, A = ? x cubic decimeter x degree Celsius, where ? is the molar absorption factor.
The stuffs we used during the experiment are Ammonium Fe ( III ) sulfate and Salicylic acid. Therefore, we used the undermentioned method to find the concentration of the Fe ( III ) – salicylic acid composites.
Materials and Methods:
500 cm3 of Ammonium Fe 500 cm3 of salicylic acerb solution
( III ) sulphate solution was prepared. was prepared.
Transferred into burette
A series of mixture was prepared in each trial tubing and the volume of the solution added was in the tabular array below.
Fe3+ solution ( milliliter )
Salicylic acid ( milliliter )
Table 1 The Mole fraction of each constituent
Optical denseness of the other samples were determined utilizing the same instrument and wavelength.
The most suited wavelength for measurement was determined.
These mixture was so measured utilizing spectrometer over the scope of 350-700nm.
From the spectrum, the maximal extremum has a wavelength of 531.5 nanometers.
With the same wavelength, we obtained the undermentioned Optical density for different samples and the information was recorded in the undermentioned tabular array.
Salicylic acid ( cm3 )
Fe ( III ) ( cm3 )
A graph of Absorbance against mole fraction was plotted.
From the graph, X = 0.495
To acquire y,
Y = ax / a ( 1-x )
Y = 0.495 / ( 1- 0.495 )
=0.98 ? 1
So the molecular ratio of the Fe3+- salicylic acid composite is 1: 1
A graph of Abs against mole fraction of L was drawn.
From the consequences above, the molecular ratio of the Fe3+- salicylic acid composite by utilizing Job ‘s method was 1:1. The composite is formed by which the salicylic acid donated its lone brace negatrons from hydroxyl O atom to press metal. This is because, salicylic acid is a bidentate to the metal ion. Therefore, it needed three salicylic acid to donate its lone brace negatrons to the Fe ( III ) ion. So, the composite formed is trisalicylateferrate ( III ) . The construction will be drawn as follow:
Figure 1- trisalicylateferrate ( III ) composite
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In this experiment, we measured the optical density of our samples from UV-Vis spectrometer. The sample was poured into a cuvette. The sample was non destroy which means that with the utilizing of this spectrometer, the sample was non- destructive. The UV- Vis visible radiation base on balls through the cuvette and the visible radiation was absorbed by the sample. Therefore, the sample must be in liquid signifier.
Besides that, before commixture of Fe3+ and salicylic acid, the two solutions were colourless. However, after blending the two solutions, the sample had a violet in coloring material. So, they can absorb seeable visible radiation and because of the negatrons from 500 orbital was excited from one to another electronic province. The complex gave violet in coloring material is because it absorbed green visible radiation and allow the other visible radiation passed through. Green visible radiation is a complementary coloring material to the violet visible radiation, so the complex gives the maximal optical density at wavelength 531.5 nanometer.
In add-on, we usually will choose the maximal optical density is because its sensitiveness to the concentration of the solution is the greatest at the maximal wavelength. If the ?max is non the analytical wavelength, strong radiation may be strongly absorbed and caused divergence from the Beer Lambert Law. However, in this experiment, if let say we did non utilize the?max, the consequence we obtained from graph will non be affected much. We will besides necessitate to round off it to integer so that we can acquire the ratio.
Furthermore, stoichiometry expression of a complex ion can be obtained through uninterrupted fluctuation method. Besides that, this method is really help in the keeping the figure of moles of the sample throughout a series of different mixture in the sample. However, merely different is the mole fraction of the different samples.
The maximal extremum for Fe ( III ) -salicylic acid composite was 531.5 nanometer.
The molecular ratio of the Fe3+- salicylic acid composite is 1: 1