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What Is Job’s Method In Chemistry

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Inorganic Chemistry Lecture 90 ( Job’s Method and Mole Ratio Method)
  • Spectroscopy: Spectroscopy is the method of imparting electromagnetic radiation on a body and recording its reaction to it. Used to measure samples by absorption spectroscopy. Also, in measuring toxic samples in blood.
  • Chromatography: When the substance to be texted is impure, forensic chemists use chromatography. Chromatography breaks down the mixture into its component constituents which can be analyzed separately.

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What Is The Difference Between Jobs Method And Mole Ratio Method

Jobs method is a process we can use in analytical chemistry to determine the stoichiometry of binding of different chemical species. The key difference between Jobs method and mole ratio method is that in Jobs method the molar concentrations of reactants are held a constant while, in mole ratio method, the molar concentration of a reactant is kept constant and the molar concentration of other reactant varies. Jobs method is the most common method for the determination of stoichiometry of binding event while mole ratio method is an alternative method for Jobs method.

Below infographic summarizes the difference between Jobs method and mole ratio method.

What Is Forensic Chemistry

Forensic Chemistry can be defined as the practice of application of our knowledge in the field of chemistry to solve crimes. A forensic chemist can assist in the identification of unknown materials found at a crime scene

There are several methods that a chemist can adopt from chemistry to help solve uncertainties at a crime scene. Forensic chemists use a variety of instruments to identify unknown substances found at a scene.

Some examples of applications of forensic chemistry

  • Spectroscopy techniques are used to check the purity of materials.
  • Detecting illegal drugs and narcotics using identification and separation techniques.

As we know, every subdivision of science has its foot in one or the other aspect of our lives. From developing technologies improving the quality of the food we eat to sending rockets to space, science is everywhere. Let us look at one such field of science known as Forensic Chemistry.

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Summary Jobs Method Vs Mole Ratio Method

Jobs method is a process we can use in analytical chemistry to determine the stoichiometry of binding of different chemical species. Mole ratio method is an alternative method for Jobs method. The key difference between Jobs method and mole ratio method is that in Jobs method the molar concentrations of reactants are held constant while in mole ratio method the molar concentration of a reactant is kept constant and the molar concentration of other reactant varies.


1. Jobs Method. Scribd, Available here.2. Job Plot. Wikipedia, Wikimedia Foundation, 25 Sept. 2019, Available here.3. Mole-Ratio Method for Determining Metal-Ligand Stoichiometry. Image and Video Exchange Forum, Available here.

Image Courtesy:

1. Synthesis of nano-TiO2 stellerite composite By Vicente Neto Own work via Commons Wikimedia

Complex Ion Composition Determination By Jobs Method

8. Job

Inorganic Chemistry

Writing Objective: Laboratory Report

The composition of the complex ion nickel ethylene-diamine, Nix. in aqueous solution, is determined by the method of continuous variations, or Jobs method.

Often in inorganic chemistry, two or more species can interact to form a complex that cannot be isolated as a stable compound. In this case, the composition of the complex must be determined by other methods. One such method, the Jobs method, is concerned with evaluating n for the equilibrium below. In this experiment Z is Ni2+ and L is the ligand ethylenediamine .

Experimentally, the absorption at a given wavelength of a series of solutions containing varying molar fraction of Z and L is measured. If the equilibrium lies far to the right in equation , then the absorption will be greatest when the in the solution Is exactly n times greater than . Therefore, we can determine n and thus the composition of ZL by knowing the ratio of L to Z in the solution that contains a maximum absorbance of ZLn.

Depending on the value of the equilibrium constants, certain species will predominate in solution.

where K is the equilibrium constant for the reaction . Since the condition of a maximum in a curve of [ZLnl verses X is that we can differentiate equations , , and with respect to X and combine the differential equations with equations , , and to yield.

The difference between Ameas and AZ+L Is denoted as Y Where Az is the absorbance of the pure M molar N12+ solution.

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Simple Observable Associations: Main Group Metals

One finds a seemingly disproportionate use of MCV by maingroup organometallic chemists. This may arise from a relatively greater emphasis on solvation, aggregation, and Lewis acid-base complexation or simply from different cultural biases.

Taylor and co-workers reported that borinic esters can effect the regioselective monofunctionalization of diols. Rate studies combined with MCV determined that the resting state in the catalytic cycle was a 1:1 complex 18 constituted from diol 16 and borinic acid 17 .

Organolithium chemists have gravitated toward MCV, possibly owing to their requisite obsession with aggregation and solvation. Tokitoh and co-workers isolated unsolvated lithium diketiminate 19 as a crystalline solid. MCV revealed that solvation by tetrahydrofuran affords a 1:1 complex , presenting a direct measure of the primary solvation shell. The equilibrium constant was determined independently through a titration experiment rather than via the Job plot.

Brown and co-workers investigated the solvation of ethyllithium hexamer by triethylamine . The change in dielectric constant of the mixture accompanying formation of disolvated ethyllithium dimer was monitored. When the mole fraction is normalized per subunit, the maximum occurs at XA = 0.5, showing the 1:1 Et3N-Li ratio. Although we are somewhat surprised by the dimer assignment, this represents one of the earliest measurements of a lithium ion solvation number.

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We are looking for a dedicated, analytical chemist to be responsible for studying the chemical make-up of materials that are essential in manufacturing business to ensure product safety. The chemist’s responsibilities include preparing test solutions, analyzing organic and inorganic compounds, and conducting quality control tests. The Chemist will conduct research and explore how products, processes, and equipment may be improved.

To be a successful chemist, you should be analytical, detail oriented, and logical. You should be dedicated to furthering scientific knowledge and improving processes and products.

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Popular Chemistry Degree Jobs

If you have a bachelor’s or master’s degree in chemistry, there are many great careers you can pursue. You may consider many fields, such as science, research, healthcare, or business. Knowing more about the roles you can pursue with a chemistry degree can help you find a career that suits your interests and skills. In this article, we explore 15 chemistry degree jobs, their national average salary, and primary job duties.


Here is a list of 15 jobs you may consider that require a chemistry degree:

What Is Jobs Method

Organic Chemistry – Basic Introduction

Jobs method is an analytical technique we can use to determine the stoichiometry of a binding event by keeping the molar concentrations of reactants constant. This method is named after the scientist Paul Job, who developed the technique in 1928.

Let us consider an example to understand the method. Consider a reaction mixture which has two chemical species that can bind with each other. The stoichiometry for this binding reaction can be obtained using the Jobs method. This means we dont know exactly how much of B binds with D, or vice versa. Using this method, we can find these exact amounts. For this determination, we have to keep the sum of the molar concentrations of binding partners constant. However, their molar fractions may vary. Therefore, we can run an experiment in order to get readings for the mole fraction and the physical property that we are going to measure. i.e. UV absorbance.

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What Is A Job Plot

Imagine the binary complexation in eq 2. Complexation could be probed by holding the concentration of B fixed, systematically varying the concentration of A, and monitoring a physical property, P, that serves as a proxy for the concentration of binary complex AB . The asymptotic approach to complete conversion to AB is often referred to as saturation. The curvature provides the relative stoichiometries of A and B and even a quantitative measure of binding but only to the most discerning eye or with the aid of a nonlinear least squares fit. An analogous plot could be obtained by holding the concentration of A constant and varying the concentration of B. Taken together, the two plots provide insights into the relative stoichiometries of A and B.

Plot showing saturation indicative of full conversion of A to AB with increasing concentration of A .

Instead of varying the concentration of one component at a time, MCV holds the total concentration of added A and B constant and varies the relative proportions of A and B. The units on the x axis morph from concentration to mole fraction of A or B . The use of mole fraction or its equivalent along the x axis is shared by all Job plots. The result is a very different view of the same equilibrium .

Job plots corresponding to the binary 1:1 combination using a normalized physical property, P, and Keq = 1, Keq = 10, and Keq = 100.


Job plots corresponding to the binary 2:2 combination.

What Is The Difference Between Quantitative And Qualitative Chemistry

The difference between qualitative and quantitative analysis in chemistry is that the qualitative analysis does not measure the amount of the substance but measures the quality of that material whereas quantitative analysis in chemistry gives the absolute or relative quantity regarding the concentration of one or more substances present in a sample or compound.

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Job’s Method Of Continuous Variation

The equilibrium of complexometric reaction between metal and ligand can be represented as

The stoichiometry of MLn can be determined by knowing the value of n. In this method, a series of solution of metal ion and ligand is prepared where the total numbers of moles of metal and ligand remain constant means nM and nL are variables, whereas is constant. Now, the absorbance of all solution are monitored at a particular wavelength where the metal-ligand complex is only absorbing, but metal and the ligand are non-absorbing.

The graph is plotted between absorbance and mole fraction of ligand/metal. Two linear graphs are obtained one when mole fraction of ligand is plotted versus absorbance and another for mole fraction of metal versus absorbance. The point of intersection represents the stoichiometric composition of metal complex which is equal to XL/XM.


For exampleFe2+ o-phenanthroline Fe2+ o-phenanthroline Fe32+

Observations On Job’s Method Of Continuous Variations And Its Extension To Two

What Is Job Analysis? Components, Process, Methods, Uses

H. Irving and T. B. Pierce,J. Chem. Soc., 1959, 2565DOI: 10.1039/JR9590002565

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Applications Of Analytical Chemistry

Some important applications of this branch of chemistry are listed below.

  • The shelf lives of many medicines are determined with the help of analytical chemistry.
  • It is used to check for the presence of adulterants in drugs.
  • Soil can be tested to check for appropriate concentrations of minerals and nutrients that are necessary for plant growth.
  • It is employed in the process of chromatography where the blood samples of a person are classified.
  • The concentration of the pesticide residues and the contaminants in a given food sample can also be determined via analytical chemistry.
  • It also has many important applications in medicine, with its use in the testing of cholesterol and glucose levels in a blood sample.
  • Analytical chemistry is an integral part of forensic science, clinical analysis, and even environmental analysis.

Thus, a brief introduction to the field of analytical chemistry is provided in this article. To learn more about this branch of chemistry along with other branches, such as inorganic chemistry, register with BYJUS and download the mobile application on your smartphone.

Capillary Electrophoresis Facilitates Determination Of Metal Complex Stoichiometry By Jobs Method Of Continuous Variation

A Department of Geography and Environmental Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.

B Corresponding author. Present address: Whitman College, Hall of Science, 345 Boyer Avenue, Walla Walla, WA 99362, USA. Email:

Environmental Chemistry 10 409-416 Submitted: 5 June 2013 Accepted: 5 September 2013 Published: 25 October 2013

Environmental context. Knowledge of metal-chelating agent speciation is integral to our ability to predict and interpret the behaviour of synthetic chelating agents in the environment. Capillary electrophoresis can be used to separate metalligand complexes with similar spectroscopic characteristics but different stoichiometries, thereby providing insight into metalligand speciation that is not possible by any other technique. Here, we demonstrate the utility of capillary electrophoresis for the determination of metalligand stoichiometries and evaluate its limitations.

Additional keywords: chelating agent, diethylenetriaminepentaacetic acid, equilibrium speciation, nickel, polynuclear complex.

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Chemist Skills & Competencies

In addition to formal education, certain soft skills, or personal qualities with which you were either born or acquired through life experience, will contribute to your success in this occupation. They are:

  • Problem Solving and Critical Thinking Skills: Your work as a chemist will identify problems and come up with possible solutions to them. Before implementing those fixes, you will have to evaluate each one and then predict which one will be the most effective.
  • Speaking, Listening, and Interpersonal Skills: Since your job is likely to involve working on a team, the ability to communicate with others is essential.
  • Time Management Skills: Excellent time management skills will allow you to meet deadlines.
  • Analytical Skills: Chemists, like other scientists, must analyze a lot of data
  • Organizational Skills: Strong organizational skills will be needed to keep track of your data, and carefully document all processes and results.

Education Training & Certification

Colorimeter 2: Job’s Method (Method of Continuous Variation).

A chemist job requires at least a four-year college degree, although there are benefits to pursuing higher levels of education.

  • College degree: If you want to be a chemist, you will need to earn at least, a bachelor’s degree in chemistry. However, most research jobs require a master’s degree or, more likely, a Ph.D.
  • Internships: While not mandatory, an internship, work-study program or fellowship can help students gain experience while completing their degree, to help make them better job candidates.
  • Experience: With experience and advanced education in the form of a doctorate, chemists can become lead researchers. Additional experience can mean assignments that include working on bigger and more complex projects.

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One Part Of Chemistry

1. To verify the Beer-Lambert Law

2. To determine the composition of complexes by using Job Method


Job method is also known as method of continuous variation. This method is used to determine the composition of a complex which is formed by two reacting species. It is most effective to be applied when only a single complex is formed in the solution. Jobs method is based on the concept that equimolar solution of metal-ion and ligand are mixed gradually by using different volume ratio. As the concentration of metal ion increase, the concentrations of ligand will decerease. It maintains the total number of mole reactants to be constant in a series of mixture of reactants. In this experiment, the mixture is made up of different fraction of nickel sulfate and ligand ethylene diamine. A wavelength at which the complex absorbs the strongest, max is selected. Then, the absorbance of each solution in the series at the wavelength of maximum absorbance is determined by using spectrometric method.

Job Method is often used to determine the soluble Ni2+ – en complexes in the solution. The n value of the complexes also can be calculated.

Z + nL à ZLn

where Z represents Ni2+ ion, L refers to the ethylene diamine . Different complexes could be formed in a mixture of metal Ni2+ ion and ligand en, for example, Ni2+, Ni22+, Ni32+ and many more. The equilibrium constant of each Ni2+ – en complexes are shown in the following:

Diagram 1




n1 =X /

Difference Between Jobs Method And Mole Ratio Method

November 21, 2019 Posted by Madhu

The key difference between Jobs method and mole ratio method is that in Jobs method, the molar concentrations of reactants are held a constant, while in mole ratio method, the molar concentration of a reactant is kept constant and the molar concentration of other reactants varies.

Jobs method is a process we can use in analytical chemistry to determine the stoichiometry of binding of different chemical species. Mole ratio method is an alternative method for the Jobs method. However, both techniques are useful in different occasions.

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What Is Mole Ratio Method

Mole ratio method is an alternative method for Jobs method. In this method, the molar concentration of one reactant varies, and the molar concentration of other reactant is constant. Here also, we can determine the stoichiometry of a binding event by plotting a graph using the molar fractions and a physical property that varies with the formation of the complex by binding two chemic species.

Figure 01: Use of Mole Ratio Method in the Synthesis of Nano Titanium Dioxide

Generally, the physical property is UV absorption .

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