How to Calculate Theoretical And Practical Yeild

Calculation of % Yield Percent Yield: The percentage yield is the ratio between the actual yield and the theoretical yield multiplied by 100%.  It indicates the percent of theoretical yield that was obtained from the final product in an experiment.  The general mechanism for finding percentage yield is as follows:  1.  Balance the chemical equation 2.  Find the limiting reagent 3.  Find the theoretical yield 4.  Find the actual yield 5.  Find the percentage yield     1.  Balancing The Chemical Equation: The first step in finding theoretical and percentage yield is to balance the relevant chemical equation.  The first step in balancing any equation, is to write out the correct chemical formula: For Example:           CH4 + O2 -->  CO2 + H2O Is the reaction for the combustion of methane (CH4) in excess oxygen (O2) To balance the equation, you need to find the smallest whole number coefficients so that each element is balanced in the reaction. To solve for these coefficients, use a system of equations:  For the current example:                               aCH4 + bO2 -->  cCO2 + dH2O Multiplying each element by the coefficient gives you the following equations: Equation 1: a = c When the equation is balanced, there will be (1 x a) Carbon atoms from methane on the reactants side and (1 x c) Carbon atoms from carbon dioxide on the products side Equation 2: 4a = 2d When the equation is balanced, there will be (4 x a) Hydrogen atoms from methane on the reactants side and (2 x d) hydrogen atoms from water on the products side Equation 2(i): 2a = d Note that Equation 2 can be simplified to this format Equation 3: 2b = 2c + d When the equation is balanced, there will be (2 x b) oxygen atoms from oxygen gas on the reactant side, (2 x c) oxygen atoms from carbon dioxide on the products side and (1 x d) oxygen atoms from water on the product side. Equation 3(i): b = 2a Note that this formula results by substituting Equation 1 and Equation 2(i) into Equation 3 and simplifying  To solve for a, b, c and d: First take the smallest whole number that satisfies Equation 1, which is simply a = c =1 Then, substitute that value into Equation 2(i): 2a = d 2(1) = d d = 2 and Equation 3(i): b = 2a b = 2(1) b = 2 Your coefficients are a = 1, b = 2, c = 1 and d = 2 When writing your balanced equation, the coefficient 1 is assumed and can be omitted, yielding the formula:                    CH4 + 2O2 -->  CO2 + 2H2O 2.  Finding The Limiting Reagent:  This is the reactant which the product yield depends on, as it is not in excess. To determine which reactant is the limiting reagent:-     1(a). Divide the mass (in grams) of the reactant by its molecular weight (g/mol)                                                                   OR      (b). Multiply the amount used (in ml) by its density, then divide by its molar mass                   2.  Multiply the mass (your answer from steps 1(a) or 1(b)) by the number of moles of the reactant used in the reaction. Example:  salicylic acid + acetic anhydride « acetylsalicylic acid (ASA) + acetic acid Salicylic acid:  (0.211 g) / (138.1 g/mol) x 1 = 0.00153 mol Acetic anhydride:  (0.480 mL) x (1.08 g/mL) / (102.1 g/mol) x 1 = 0.00508 mol Therefore, salicylic acid is the limiting reagent, since there are less moles of that than there are of acetic anhydride. Pic source: www.khanacademy.org 3.  Theoretical Yield:

This is how much product will be synthesized in ideal conditions. To determine theoretical yield, multiply the amount of moles of the limiting reagent by the ratio of the limiting reagent and the synthesized product and by the molecular weight of the product.

Example: Theoretical Yield salicylic acid + acetic anhydride « acetylsalicylic acid (ASA) + acetic acid Theoretical yield =     0.00153mol sal. acid x      1 molASA      x   180.2g ASA   .                                           1 mol sal. acid          1 mol ASA                                                            = 0.276 g ASA Therefore, in a perfect experiment, 0.276 g of acetylsalicylic acid will be synthesized

Pic Source: www.premedhq.com

4.  Find the actual yield:

The actual yield you got after the completion of the reaction. 

                

5.  Percent Yield:

  

The percentage yield can be calculated using the mass of the actual product obtained and the theoretical mass of the product calculated using the balanced equation of the reaction.

Percentage Yield =     Mass of Actual Yield       x   100%

                  Mass of Theoretical Yield

The Principles of Green Chemistry

Green Chemistry

Chemists and chemical engineers applying green chemistry look at the entire life cycle of a product or process, from the origins of the materials used for manufacturing to the ultimate fate of the materials after they have finished their useful life. By using such an approach, scientists have been able to reduce the impacts of harmful chemicals in the environment.

Research and development in the field of green chemistry are occurring in several different areas.

Alternative feedstocks

Historically, many of the materials used to make products often were toxic or depleted limited resources such as petroleum, but green chemistry research is developing ways to make products from renewable and nonhazardous substances, such as plants and agricultural wastes. For example, cellulose and hemicellulose, which constitute up to eighty percent of biomass, can be broken down to sugars, then fermented to chemical commodities such as ethanol, organic acids, glycols, and aldehydes. Converting biomass to ethanol has become economically and technically viable due to a new class of genetically modified bacteria capable of breaking down the different sugars in hemicellulose.

Benign manufacturing

The methods used to make chemical materials, called synthetic methods, have often employed toxic chemicals such as cyanide or chlorine. In addition, these methods have at times generated large quantities of hazardous wastes. Green chemistry research is developing new ways to make these synthetic methods more efficient and to minimize wastes while also ensuring that the chemicals used and generated by these methods are as nonhazardous as possible. For example, a number of industries, such as the pulp and paper industry, use chlorine compounds in processes that generate toxic chlorinated organic waste. Green chemists have developed a new technology that converts wood pulp into paper using oxygen, water and polyoxometalate salts, while producing only water and carbon dioxide as by-products.

Designing safer chemicals

Once it is certain that the feedstocks and methods needed to make a substance are environmentally benign, it is important to ensure that the end product is as nontoxic as possible. By understanding what makes something harmful (the field of molecular toxicology), scientists are able to design the molecular structure so that it is not dangerous.

Green analytical chemistry

The detection, measurement, and monitoring of chemicals in the environment through analytical chemistry have long been a tool for environmental protection. Instead of measuring environmental problems after they occur, however, green chemistry seeks to prevent the formation of toxic substances and thus prevent such problems. By making sensors and other instruments part of industrial manufacturing processes, green analytical chemistry is able to detect even tiny amounts of a toxic substance and to adjust process controls to minimize or stop its formation altogether. In addition, although traditional methods of analytical chemistry employ substances such as hazardous solvents, green analytical methods are being developed to minimize the use and generation of these substances while conducting analysis.

Principles

Paul Anastas, then of the United States Environmental Protection Agency, and John C. Warner developed 12 principles of green chemistry, which help to explain what the definition means in practice. The principles cover such concepts as:

• the design of processes to maximize the amount of raw material that ends up in the product;
• the use of safe, environment-benign substances, including solvents, whenever possible;
• the design of energy efficient processes;
• the best form of waste disposal: not to create it in the first place.

The 12 principles are:

1. It is better to prevent waste than to treat or clean up waste after it is formed.

2.  Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

3. Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

4. Chemical products should be designed to preserve efficacy of function while reducing toxicity.

5. The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary wherever possible and, innocuous when used.

6.  Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.

7.  A raw material or feedstock should be renewable rather than depleting wherever technically and economically practicable.

8.  Reduce derivatives - Unnecessary derivatization (blocking group, protection/ deprotection, temporary modification) should be avoided whenever possible.

 9.   Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

10.  Chemical products should be designed so that at the end of their function they do not persist in the environment and break down into innocuous degradation products.

11. Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.

12. Substances and the form of a substance used in a chemical process should be chosen to minimize potential for chemical accidents, including releases, explosions, and fires.

  

What Is Chemistry?  

"Livings are biology but Life is Chemistry"

Chemistry is the science of the composition, structure, properties and reactions of matter, especially of atomic and molecular systems.

Life itself is full of chemistry; i.e., life is the reflection of a series of continuous biochemical processes. Right from the composition of the cell to the whole organism, the presence of chemistry is conspicuous. Human beings are constructed physically of chemicals, live in a plethora of chemicals and are dependent on chemicals for their quality of modern life. All living organisms are composed of numerous organic substances. 

The readership of this blog could extend up to the students & researchers of various subject areas within, Chemical Sciences, Pharmaceutical Sciences, Food Sciences, Life Sciences and Health Sciences etc

Emerging Fields of Research in Chemistry

Green Chemistry:- Over the past few years, the idea of chemistry has been mobilized to develop new techniques that are less hazardous to human health and the environment. This new approach has received extensive attention and goes by many names including Green Chemistry, Environmentally Benign Chemistry and Clean Chemistry. Green Chemistry with its 12 principles would like to see changes in the conventional ways that were used for decades to make synthetic organic chemical substances and the use of less toxic starting materials. By changing the methodologies of organic synthesis health and safety will be advanced in the small scale laboratory level but also will be extended to the industrial large scale production processes through the new techniques.

 

Synthon approach:- Synthon approach is a very useful analytical approach to Organic synthesis in which the target molecule is broken into fragments through a series of logical disconnection to get the best possible and likely starting or building blocks for the target molecule. In each case the starting material is converted to some desired compound, the target molecule through some key intermediate. Actually, a number of synthetic routes can be written for a given target molecule. But in actual synthesis, generally that route is selected which is economical, safe, and easy to carry out and produces maximum yield in a short reaction time. 

Combinatorial chemistry:- Searching for a compound with the desired biological activity, the more compounds we can screen the more likely we are going to find a useful lead compound.  The traditional method of medicinal chemistry concerned the preparation, purification and characterization of individual compounds. if this process is speeded up then faster progress can be made. In the process of finding new drug candidates medicinal chemists nowadays have a variety of options to choose from, one is to apply combinatorial chemistry techniques. The technique of combinatorial chemistry (‘CombiChem’) has helped the way chemists go about searching for lead compounds and also at the stage of lead optimization. Applying these techniques has resulted in the production of large numbers of compounds. A trend is observed towards smaller libraries of compounds with more drug-like properties.

Chemical Category Formation Read-across analysis:- Chemical category formation and subsequent read-across analysis have been suggested as the scientific method. In this approach scientific background are using the formation of chemical categories, or groups, of molecules to allow for read-across i.e. the prediction of toxicity from chemical structure. The approaches to perform read-across within a chemical category are also described without the excessive use of animals.

                                                       
Green solvents:- The use of hazardous and toxic solvents in chemical synthesis considered a very important problem for the health and safety of researchers, students, workers and environmental pollution. Green Chemistry aims to exchange the use of toxic solvents with greener alternatives, with replacement and synthetic techniques, separation and purification which do not need the use of solvents. Green Chemistry has placed the solvent issue of synthetic organic chemistry and practices in their use at the same level with alternative synthetic routes in chemical industry. Green solvents have been characterized for their low toxicity, higher low solubility in water (low miscibility), easily biodegradable under environmental conditions, high boiling point (not very volatile, low odor, health problems to workers) and easy to recycle after use.

In silico studies:- The use of computers and computational methods permeates all aspects of drug discovery today and forms the core of structure-based drug design. Drug discovery is mostly portrayed as a linear, consecutive process that starts with target and lead discovery, followed by lead optimization and pre-clinical in vitro and in vivo studies to determine if such compounds satisfy a number of pre-set criteria for initiating clinical development. In silico methods are an expression used to mean "performed on computer or via computer simulation." To test these hypotheses they have consistently used traditional pharmacology tools such as in vivo and in vitro models. Increasingly over the last decade however we have seen that computational (in silico) methods have been developed and applied to pharmacology hypothesis development and testing.

And many more.....

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