Question

1) Distinguish the processes of separation and synthesis, and state whether physical and/or chemical properties are involved for each.

2) IN BULLET FORMAT, outline and describe THREE (3) separation TECHNIQUES(not equipment or chemical/physical properties). the techniques will be chromatogrophy technique in the lab Separation by Extraction, filtration technique in the lab Synthesis of Aspirin and crystallization technique in the lab Recrystallization and include ONE specific example from the experiments for each. Highlight the key properties that facilitate those techniques.

3) Describe the determinative analyses that were used to MEASURE SUCCESS for the separation and synthesis experiments, identifying whether they were used for the separation and/or syntheses experiments. Identify each of the analyses as either qualitative and/or quantitative, and provide the associated formula(s) for each (including any units).

Answer 1

1) Separation is a method to separate mixtures into its constituent elements or compounds. Separations is done on the basis of differences in chemical properties or physical properties (such as size, shape, mass, density, or chemical affinity) between the constituents of a mixture. The constituents having large difference in their properties separate easily while the separation of constituents with small difference in their properties becomes tedious. In some cases, when no single difference can be used to carry out a desired separation, multiple operations are combined to achieve the desired end. A numerous separation techniques are available and depending on the physical and chemical nature of the substances in the mixture, the most appropriate separation technique can be choosen to separate them from the mixture.

Synthesis is a method to obtain a product by means of some chemical reactions and chemical properties of the participating entities are important for the synthesis. Synthesis begins by selection of compounds i.e. reagents or reactants which combine in a definite proportion to yield the desired products. A side reaction is an unwanted chemical reaction taking place that decreases the yield of the desired product. Some reactions directly synthesize the desired product without any side product while some results into a mixture of products due to side reactions. In case of latter, the separation technique is employed to obtain the main product and the process is commonly termed as isolation.

2)

• Chromatography: ​It is a physical method for separation which is based on differential partitioning of the constituent between the mobile phase and the stationary phase. Mobile phase is generally a solvent which runs over a fixed stationary phase. Due to difference in partition coefficient, different constituents travel with different speeds in mobile phase resulting in separation. Chromatography can be employed for both qualitative and quantitative determinations. Various chromatographic techniques are there such as column chromatography, paper chromatography, Thin Layer Chromatography (TLC). One of the best application of chromatography in laboratory is separation of amino acids in a mixture.
• Extraction: It is a separation process of separation of a substance from a matrix. This technique is based on partition theory according to which solute remains in equilibrium with two phases viz. aquous and organic.This is based on exactly how the solute move from the aquous phase into an organic layer. It is quantitative meyhod.
• Filtration is another physical technique used for separation. In filtration, the constituents are separated on the basis of solubility of constituents in a particular solvent. A solvent is choosen such that one of the constituents dissolves in it while others remain behind as residue. It is a quantitative method.

Synthesis and purification of Aspirin:

Aspirin (acetylsalicylic acid) is synthesized from saliccylic acid and acid anhydride in presence of a strong acid. Salicylic acid is reacted with an excess of acetic anhydride in presence of a small amount of a strong acid as a catalyst to speed up the reaction. Water is added at the end of the reaction, the excess acetic acid is quenched with the addition of water as acetic acid is very soluble in water while the aspirin product is not very soluble in water so it precipitate when water is added. The insoluble part (crude Aspirin product) is separated using filtration. Now the synthesized Aspirin can be tested for any side product using TLC (single spot would mean the formation of Aspirin only). Pure Aspirin is obtained by recrystallisation of the crude product in hot ethanol. Recrystallisation involves heating the saturated solution of the crude product which on cooling gives crystals of pure Aspirin which are collected using filtration technique.

3) Success of synthesis is basically determined by calculating percentage yield of the product. In order to do so, following formula is used:

where observed yield is the observed weight of the product, theoritical yield is the weight of product expected from stochiometric calculations.

More is the percent yield, more successful would be synthesis.