The experiment contains two procedures: the solubility tests, and macroscale recrystallization of chosen solutes and solvent. The solubility tests were performed with all the solutes, which were phthalic acid, naphthalene, anthracene, benzoic acid, and resorcinol. The three solvents were water, methanol, and acetic acid. Solubility tests were carried out at both low and high temperature conditions, depending on the substance. The most efficient pair was acetic acid and anthracene, which was chosen for the second part of the experiment. In the macroscale procedure, 47.57% of anthracene was recovered. The crystals had a powdery physical appearance. There were several errors in the experiment, such as loss of solids due to unnecessary transfer, …show more content…
Customarily, liquids are purified by distillation, whereas impurities from a solid can be removed by recrystallization. In fact, recrystallization is the most basic, critical method to purify a solid and allow a perfect crystalline structure to form. Recrystallization relies on the distinct solubility of solutes in a solvents. In other words, less soluble compounds tend to crystallize first. Ideally, the solvent would completely dissolve the compound to be purified at high temperature. In addition to that, the contaminant should be insoluble in that solvent at the high temperature. Recrystallization is still a powerful method of purification in modern chemical field. For instance, when organic substances are synthesized the laboratory or isolated from plants, they often contain impurities. A practical application of recrystallization is the commercial purification of …show more content…
A solute and solvent were chosen from the list to start with. Around 10 mg of solid and 0.25 mL of solvent were added to a clean reaction tube. A pipette was useful in transferring the solvent to the tube. The mixture was stirred with a glass stirring rod. If the substance was completely dissolved at room temperature, a few drops of water would then be added to see if the solid precipitated. If so, the solution would be heated to boiling point in a sand bath. The hot saturated solution was left undisturbed for a period of time, before the crystals formed. In case that the substance could not dissolve at room temperature, it would have to be heated and further observed. If the solid dissolved entirely, the substance was considered soluble in the hot solvent. On the other hand, if some but not all dissolved, it was noted as moderately soluble. Continually, the solution was allow to cool down, before it was reheated to dissolve the solid. The solution stood undisturbed until crystals were formed. Solubility tests were performed on all possible solvent-solute pairings. The most efficient pair was
The product was then suspended in 2 ml of water with a stir rod in a 50 ml Erlenmeyer flask and heated to boiling. Water was added in one milliliter increments until all the product was dissolved (18 ml added total). The saturated solution was allowed to slowly cool, and gradual white crystal formation was observed. Recrystallized product was collected once more by suction filtration with the Hirsch funnel once crystallization ceased. Collected product dried on a watch glass for a week, weighed 0.14 g (1.2 mmol), and the melting point was 139°-141°
During recrystallization, the solution was to be cooled to room temperature before placing it in an ice bath. Doing this allows enough time for the crystals to be formed because as the temperature decreases, the rate of crystallization slows down. If the solution was placed in the ice bath too quickly, then the cold would have blocked out the impurities and trapped them in the solution. The more impurities present, the lower the melting point so data would have been inaccurate. Also, if the melting point apparatus wasn’t set up correctly, the data would have been imprecise.
Phenacetin’s cold water solubility is 0.076 grams/100 mL of water, whereas its boiling water solubility is 1.22 grams/100 mL of water. In this experiment, water solubility will be an indicator for how much boiling water to use in recrystallization, which purifies the unknown precipitate produced in the second lab. If a substance has higher water solubility in boiling water, such as acetanilide compared
6. The solubility of the solids were tested using a micro tray, by placing them in water and oil to observe their polarity,
There are millions of different organic compounds. Most of them are found in mixtures and in order to achieve a pure form they need to be separated, isolated, and purified. However, there are endless numbers of possible mixtures, which make it impossible to have a pre-designed procedure for every mixture. So chemists often have to make their own procedures. The purpose of this experiment was to prepare the student to the real world by them designing their own procedure which will help them understand the techniques of separation and purification better. The goal was to extract two of the components of the
Recrystallization purifies a crude product by separating the product from impurities based on solubility. The product being purified should easily dissolve in the chosen solvent at high temperatures, but not at room temperature. Impurities should dissolve in the solvent at room temperature but not at high temperatures.
The mixture was heated at 120°C using an aluminum block and was stirred gently. After all of the solid dissolved, it was heated for 20 additional minutes to ensure the reaction was complete.
To be able to complete this experiment various lab instruments were needed. This includes the use of beakers, test tubes, a metal spatula, wooden splints, and a Bunsen burner. The analysis begins with determining the physical traits of the compound. Then 0.15 grams of the unknown substance is mixed with 3 mL of distilled water to test
Microscale involves using smaller amounts of chemicals and solids. Therefore, the purpose is to determine the density, solubility, recrystallization, extraction, separation, and drying of products by using small quantities. The mass of volume was determined by using the density formula: Density= Weight (g) / volume (mL). Solubility is defined as the extent to which a substance is soluble. Crystallization is a technique used for purifying solid compounds. The percent recovery determined how much of the substance would remain after purification by calculating: (amount of pure substance collected) / (amount of impure substance began with) x 100. The separation of two liquid layers or purifying organic reaction products is identified as extraction and is used to establish a state of equilibrium.
The solution is then cooled and recrystallization of the solute occurs. For a solvent pair to
An Erlenmeyer flask was used to accommodate the largest volume of recrystallization solvent calculated and was cooled in an ice bath to increase the yield of crystals. The solid was collected by vacuum filtration and washed with a small amount of ice water. The product is then dried to a constant mass by use of an oven and weighed. A small amount of the unknown was compared to two samples of acetanilide and phenacetin for a melting point range to determine the identity. The temperature of the unknown was recorded when the first trace of liquid can be seen and when the unknown was completely liquid.
To begin the qualitative scheme, 6 M HCl was added into the test tube containing the unknown solution. This step was essential because HCl (aq) was expected to separate the two unknown ions on the principle of solubility, the ability of an amount of a substance to dissolve in a specific amount of solvent.1 In this experiment, since the solvent
These techniques were used to produce the pure forms of sulfanilamide and fluorene. After the filtration step in the first experiment, the pure sulfanilamide appeared to be a mix of small, white and yellowish crystals, resembling a powder. However, sulfanilamide should have crystallized into large needles, which indicated that either there was too little solvent or the crystals formed too quickly. As shown on Data Table 1, the percent yield was 69%, therefore implying that the crystallization of sulfanilamide experiment was not completely successful – a lower yield will indicate purer results. Therefore, there are still amounts of impurities in the pure sulfanilamide. Several errors throughout the course of the experiment could have contributed to a high yield, such as not adding enough solvent to dissolve the solute completely, or not completely separating the crystals after crystallization. By not separating the crystals, this most likely caused the crystals to regain its yellow color; the pure sulfanilamide should have looked white. Another possible error could have not been letting the heated solution with
Recrystallization is a technique frequently used in organic chemistry to purify solid organic compounds. The goal of this technique is to allow organic compounds to form crystal lattice structures, and to remove any of the impurities that do not align within this crystal structure.1 The theory behind recrystallization revolves around entropy; as heat will cause a organic compound to dissolve (increase in entropy), a decrease in heat will then allow that organic compound to reform (decrease in entropy) and become purer.2
If the solute melts prior to the boiling of the solvent, recrystallization will not be able to occur. For example, if you wanted to purify a sample of Compound X which is contaminated by a small amount of Compound Y, an appropriate solvent would be one in which all of Compound Y dissolved at room temperature because the impurities will stay in solution and pass through filter paper, leaving only pure crystals behind. Also appropriate would be a solvent in which the impurities are insoluble at a high temperature because they will remain solid in the boiling solvent and can then be filtered out. Finally, the solvent should be volatile enough as to evaporate from the surface of the compound and be of low financial cost.