• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6
  7. 7
  8. 8
  9. 9

Recrystallization - choose the most appropriate solvent to obtain a successful recrystallization of benzoic acid.

Extracts from this document...


Title:- Recrystallization Objective:- * The first part of the experiment is to introduce us to a technique called recrystallization. This technique can be used to purify solids. * To chose the most appropriate solvent to obtain a successful recrystallization of benzoic acid. * To determine the percentage recovery. * To determine melting point to ensure that the purity of the benzoic acid. Material and Apparatus:- * Benzoic acid * Charcoal * Boiling chips * Distilled water * Ice * Erlenmeyer flask * Beaker * Hot plate * Short-stemmed funnel * Filter paper * Glass rod * Buchner funnel * Rubber tubing (hose) * Spatula * Mel-temp apparatus Procedure:- 1. 2.0 g of crude benzoic acid is weighed into a 125-mL Erlenmeyer flask. The weight of the benzoic acid is recorded to the nearest 0.1 g. 2. The apparatus is kept warm because the solubility of benzoic acid is very sensitive to temperature. 100-200 mL of water is heated to boiling in a beaker on a hot plate (with boiling chips). An Erlenmeyer flask with little water in it (with boiling chips) is also heated, and a short-stemmed funnel is rested in its neck. 3. A filter paper is fluted to fit the funnel. 4. a few boiling chips is added to the benzoic acid, then hot water is started to add until the benzoic acid is dissolved. (Once some water had been added, the flask can be kept on the hot plate to keep it hot). Note that there may be some insoluble crud in the benzoic acid, and the crud will never dissolve, no matter how much water we added. ...read more.


0.81 Triethylamine -115 90 0.726 1.4010 2.42 33.1 0.87 Trifluoroacetic acid -15 72 1.489 1.2850 8.55 13.7 2.26 2,2,2-Trifluoroethanol -44 77 1.384 1.2910 8.55 12.4 2.52 Water 0 100 0.998 1.3330 80.1 3.7 1.82 o -Xylene -25 144 0.880 1.5054 2.57 35.8 0.62 In general, the higher the dielectric constant of the solvent, the better it will dissolve ionic compounds. Test the solvent on a small amount of the compound. If a solvent doesn't dissolve the crystals when hot, or it readily dissolves the crystals at room temperature, try another solvent. Remember to always use only a minimum amount of hot solvent! In this experiment, water is the best solvent to undergo the recrystallization process of benzoic acid. Because water's boiling point is 100 ?C and water is very polar with the formula H2O. Once you have selected your solvent you are ready to recrystallize your sample. The process of recrystallization can be broken into the following steps: 1. Selection of an appropriate solvent 2. Dissolution of the solute using a minimum amount of hot solvent 3. Decoloration of the solution if necessary (with an activated form of carbon) 4. Removal of suspended solids (through filtration of the hot solution) 5. Crystallization of the solid from the solution as it cools 6. Collecting the purified solid by filtration 7. Washing the crystals with an appropriate solvent to remove impurities 8. Drying the crystals Choosing the solvent The choice of solvent is crucial; by using the best solvent we can obtain the most accuracy result. An essential characteristic of a successful solvent is that the compound be soluble in the hot solvent but insoluble in the cold solvent. ...read more.


Its salt, sodium benzoate, is produced by the neutralization of benzoic acid with sodium bicarbonate, sodium carbonate, or sodium hydroxide. The salt is not found to occur naturally. It is used a preservative in a variety of food products, such as jams, soft drinks, and cereals. Benzoic acid is also an effective food preservative, but its sodium salt is more popular, partly because it is more soluble in water than benzoic acid. The technique can be carried out by dissolving a compound to be purified in a hot solvent (or solvent mixture) and then allowing the solution to cool. If the solvent or solvent mixture is properly chosen, the compound has a decreased solubility at lo lower temperatures, and it will form crystals in the solution. The purity of a solid, and therefore the success of or need for a crystallization procedure, can be determined by taking a melting point. Recall that you used melting point determination in the Thin Layer Chromatograph Chromatography and Melting Point Determination laboratory to identify an unknown nation unknown compound. Precaution step:- * Compound being purified must be insoluble in solvent at room temperature. * Compound must be soluble in boiling solvent. * Solvent's boiling point must be lower than the compound's melting point. * An abundant quantity of crystals must be recoverable from the cool solvent. Conclusion:- * The step by step of the technique recrystallization had been learned. Most of the recrystallization processes undergo this technique. * The most appropriate solvent to obtain a successful recrystallization of benzoic acid is water due to its polarity and 100 ?C boiling points. * Benzoic acid was recrystallized with a 90% recovery using water as the solvent. * The melting point for recrystallized benzoic acid is 119.2 ?C - 120. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Aqueous Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Aqueous Chemistry essays

  1. How much Iron (II) in 100 grams of Spinach Oleracea?

    The solutions were only left for a few minutes to acclimatise, which could have resulted in the temperatures taken being inaccurate. Also as the Potassium Manganate (VII) (aq) was being added to the Oxalic Acid (aq) the temperature of it dropped or raised depending on what temperature it was already.

  2. Titration with a primary standard.

    Rinse the transfer pipette with a small volume of the prepare 0.1 M H2SO4 solution. Transfer 20 ml of the solution into a rinsed Erlenmeyer flask. Add two drops of phenolphthalein solution. Repeat this step with two more flasks.

  1. Freezing Point Depression

    (grams of solute)] � [(T) (kg of solvent)] 4. Repeat this for the 2 other unknown samples. Molecular Mass Determination From Freezing Point Depression - Part 2 Lauric acid is used as the solvent and benzoic acid is the solute.

  2. identifying an unknown compound

    (K2Cr2O7) 2,4-Dinitrophenylhydrazine (2,4-DNP) 5% Aqueous Sodium hydrogen carbonate (NaHCO3) Water Cooled condenser Clamp and stand 20ml - 400ml Beakers Measuring Cylinder Bunsen burner Phosphorous Pentachloride (PCl5) Ethanoic acid Iron(III)Chloride (FeCl3) Sodium metal (Na) Tollens Reagent Sulphuric Acid Jones's reagent (CrO3-H2SO4 in H2O) Water bath Bunsen burner/heating Mantle 1 ml of 0.5 mols hydroxylamine hydrochloride Sodium Hydroxide (NaOH)

  1. Identification of an unknown organic compound

    If this tests positive it is a ketone. Carboxylic acid Aldehydes and primary alcohols oxidize by reflux to give carboxylic acids. They normally smell like vinegar. There structural formula is: O // R---C \ O-H Water is formed when carboxylic acids are reacted with alkali's e.g.

  2. Identification of an Organic Unknown.

    OR I can determine it is an ester by negative results from previous tests. To make my experiments fair, I will try to use same amounts of the unknown in each test and will carry out all tests in the same lab under the same confounding variables, e.g. light, temperature.

  1. Lipid Identification and Chromatography

    Different solutes, from a dye to an amino acid, have different solubilities in different solutes, meaning that some solutes will dissolve more in a solvent than other solutes will. The process works by placing a sample of the solute on a piece of chromatography paper and allowing the solvent to soak up the paper.

  2. Organic compound identification.

    Chemical Tests Results 1. The green color of the universal indicator after being added proved that the compound was neutral pH. 2. The white fumes given off after testing the gas with the stopper from the concentrated ammonia bottle told us that the gas given off was HCL and this

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work