Global Relevance:From an idea I am following and completing from the CREST secondary library, according to CREST, due to white being the main colour for pills, scientists, especially forensic scientists, face a huge problem of the inability to identify which pill is which, especially when it is in powder form. As suggested, in this project, instead of actual drugs like heroin which is illegal to have in school, I will be using painkillers such as aspirin. The aim of the project that is given is to investigate the different methods of detecting these painkillers.
Drug testing is something very important that needs to be done to avoid accidents or even death. By investigating the different methods of drug testing and comparing them, I can tell which methods are suitable to use and which are not to prevent accidents from happening and allowing victims to receive the correct medical treatment. PlanThe methods that are going to be investigated, as suggested by CREST, are colourimetry, Paper and Thin Layer Chromatography and chemical tests for particular organic functional groups.
The concentration and rf of aspirin will be used as a comparison. The methods will then be compared against each other to see which method is the most suitable to identifying unknown compounds. In order to complete this project, six one hour periods are required. Each period should be used to investigate one method at least three times, to get the most accurate and reliable data. At the end of the experiment, the efficacy of each method will be known in comparison to the others.
HYPOTHESIS:The hypothesis is that the most suitable method for detecting what is present in white tablets found near an unconscious person would be Thin Layer Chromatography as it is one of the fastests methods and most reliable methods for detecting unknown compounds. This is because TLC is a very basic, accurate and commonly used technique for identifying unknown compounds and especially how pure the compound is. COLOURIMETRY Apparatus:Colourimeter and suitable filter of either green or yellow. A solution of the complex displays maximum absorption at about 530 nmLogger Pro softwareCuvettes100cm3conical flaskBunsen burner, tripod, gauze and heat proof matAspirin500cm3volumetric flasks (x2)50cm3burette100 cm3volumetric flask (x5)1 cm3pipette + pipette filler1 mol/dm-3sodium hydroxide solution0.02 mol/dm-3iron (III) chloride solutionSafety:1 mol/dm-3sodium hydroxide solution is corrosive and can cause skin burns as well as eye damage. Safety goggles and a lab coat must be worn. Iron (III) chloride solutions are an irritant at concentrations greater than 0.02 mol/dm-3. Note: The volumetric flasks need to be washed thoroughly before being used to make a new solution, as does the pipette which should also be rinsed 2-3 times before measuring out the required volume. Method: Preparing standard solutions and obtaining a calibration graphGather all equipmentWeigh accurately about 0.4g of aspirin into a 100cm3conical flask, add 10 cm3of 1mol/dm-3sodium hydroxide solution and warm the mixture gently at 50″ for ten minutesUse a burette to measure 10cm3of stock solution into a 100cm3volumetric flask. Make it up to the volume with 0.02 mol/dm-3iron (III) chloride solution. This is standard solution A. In a similar way make up standard solutions B to G using 8cm3, 6cm3, 4cm3, 2cm3, 1cm3and 0.5cm3of stock solution. Standard SolutionVolume of stock solution (cm3)Concentration equivalent of aspirin (g/dm-3)A100.08B80.064C60.048D40.032E20.016F10.008G0.50.0044. Measure the absorbance of each standard solution using the colorimeter, fitted with a suitable filter5. Plot a graph of absorbance against concentration equivalent of aspirin on logger pro software. This is the calibration graph. Graph and AnalysisConcentration vs. AbsorbanceMethod: Analysing aspirin tabletsMake a note of the mass of aspirin the manufacturer states in each tablet. This is given on the packaging.Weigh accurately one tablet and put it into a 100cm3 conical flask. Carefully crush the tablet with a stirring rod and add 10cm3of 1mol/dm-3sodium hydroxide solution and warm at 50″ gently for ten minutes.Cool the solution and transfer quantitatively to a 500cm3volumetric flask, if necessary filtering to remove any insoluble material. Make up to the mark with deionised water. Pipette 5cm3into a 50cm3volumetric flask. Make it up to volume with 0.02mol/dm-3iron (III) chloride solution. Measure the absorbance of the unknown using the colourimeter, fitted with a suitable filter. Use the calibration graph to determine the concentration of aspirin in the solution and use this to work out the mass of aspirin in the tablet. Mass of aspirin tablet: 500mgMass of aspirin in unknown: 140mg 2. Thin Layer ChromatographyApparatus: Aspirin Tablets (3x)TLC plates PencilRuler Ethanol DichloromethaneCapillary TubesEthyl EthanoateUV lampMortarPestleSafety: Lab coats and safety goggles must be worn as ethanol and ethyl ethanoate are flammable. Ethyl Ethanoate is volatile and dichloromethane can cause irritation when in contact with the skin and eyes. Method: Take a TLC plate and using a pencil draw a line across the plate about 1 cm from the bottom.Crush the aspirin using the mortar and pestle Make up 5cm3of solvent by mixing equal volumes of ethanol and dichloromethane in a test tube. Add 1cm3of solvent to the crushed aspirin to dissolve it. Use a capillary tube to spot the sample onto the tlc plate. Allow the spots to dry and then repeat it three more times. The spots should be about 1-2 mm in diameter. After the spots dry, place the tlc plate in the developing tank and make sure that the pencil line is above the level of the solvent ethyl ethanoate. Place a lid on top and place it in the fume cupboard until the solvent has risen to within few millimetres of the top of the plate. Remove the plate and mark the position of the solvent front. Observe the plate under a short wavelength UV lamp and mark any spots observed. Repeat steps 4-7 with the unknown sample and calculate the rf values of each substanceTLC of AspirinTrial 1 Trial 2Trial 3AverageRf 0.440.450.450.45TLC of Unknown ATrial 1Trial 2Trial 3AverageRf0.240.250.240.24TLC of Unknown BTrial 1Trial 2Trial 3AverageRf0.600.630.600.613. Chemical Tests for particular organic functional groups (Carboxylic Acid)Apparatus:Sodium BicarbonateAspirin TabletsEthyl Alcohol (ethanol)Concentrated Sulphuric AcidWater Bath WaterMortar and PestleMethod: Sodium Bicarbonate TestTake the aspirin tablet and crush it into a powderAdd aqueous sodium bicarbonate to the powder by mixing the powder in waterEffervescence is observed, indicating that a carboxylic acid is presentRepeat 3 times for accurate resultsMethod: Esters TestCrush another aspirin tablet into powder using a mortar and pestleAdd 1 ml of ethanol to the powderAdd 1-2 drops of concentrated sulphuric acidHeat the reaction in a water bath at about 60″ for about 5 minutes Pour the substance into waterA fruity smell is produced Repeat 3 times for accurate resultsSodium Bicarbonate TestTrial 1Trial 2Trial 3ResultEffervescence was seenEffervescence was seenEffervescence was seenCarboxylic Acid presentEsters TestTrial 1Trial 2Trial 3ResultAbsentPresentPresentCarboxylic Acid was presentConclusion Thin Layer Chromatography is a method where a sample of an unknown is placed on a plate and the different parts of the mixture are separated. TLC also determines the purity of the compound and the different parts of it. In addition, TLC is a relatively inexpensive way to test substances as I was able to complete this test really easily. The TLC is very sensitive, as well as fast, making it the most suitable method for testing and identifying the unknown drugs, allowing me to compare it with the rf of aspirin, giving me very close results three times round. I have learned that colorimetry is a very sensitive method used to detect drugs in solution due to the use of very accurate and specialised equipment. What makes it unreliable is the fact that people, and in this case scientists, may see colours differently from each other and also because of the lighting conditions not always being favourable, chances of inaccuracy are high, making it unsuitable. Chemical Testing for particular organic functional groups allows scientists to distinguish the different compounds from each other by the way they behave. This method was not very sensitive as the results that took place when I tested the compounds could happen with any unknown compound in the same functional group. As a result, I could not get very accurate results, making this method the least reliable out of the three. Therefore, I can conclude that the most suitable method for testing and identifying drugs would be the TLC, followed by colourimetry and then testing their organic functional groups. EvaluationSources of Error which could result in inaccuracyRectificationParallax error in adding solution to a volumetric flaskBeing very careful and not shaky or nervous when pouring the solution, otherwise the entire concentration will changeUnexpected spots seen during the TLCCareful not to touch the TLC Plate. The TLC plate immediately gets fingerprints which could affect the results of the test.
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