Activities - Benjamin-Mills

More documents

Recommendations

Info

INVESTIGATING THE CHEMISTRY OF THE –OH GROUP IN VARIOUS ENVIRONMENTSWM3Part 2: Comparing different alcohols1 Place about 1 cm depth of 0.1 mol dm –3 potassium dichromate(VI) solution ina test-tube. Add 2 mol dm –3 sulphuric acid until the tube is half full. Thendivide this mixture as equally as possible between five test-tubes.You are going to investigate the effect of this oxidising mixture on a rangeof alcohols, for example ethanol, propan-1-ol, butan-1-ol, butan-2-ol and2-methylpropan-2-ol.2 Add 3 drops of one of the alcohols to the oxidising mixture in one of thetubes. Be careful not to add too much alcohol. (CARE Alcohols are highlyflammable. Keep the bottle well away from naked flames.)Carefully warm the contents of the tube until they just begin to boil.(CARE Do not continue to boil the liquid in case alcohol vapour catches fire.)3 Label the tube and leave it to stand. Repeat the procedure in step 2 witheach of the other alcohols.4 Make a note of any changes of appearance of the mixtures in the tubes. Workout what has happened in each case, and present your results in the form ofa table showing the structural formulae of the alcohols and any productswhich are formed.QUESTIONSc There is a pattern in the behaviour of the alcohols towards oxidation.Describe the pattern.d There are three different structural types of alcohol in this investigation.Suggest why the three types behave differently. Building models of aseries such as butan-1-ol, butan-2-ol and 2-methylpropan-2-ol mighthelp you see more clearly what is happening.AS LEVEL„ Salters Advanced Chemistry 2000 – see Copyright restrictions143
WM4Interpretation of themass spectrum ofsalicylic acidIn this activity you will practise some of the ideas youare learning about mass spectrometry, and see howchemists can identify a substance from its massspectrum.Before starting the activity you should be familiarwith the technique of mass spectrometry. If necessary,read about this in Chemical Ideas 6.5.This activity guides you through a sequence of steps which a chemist could takewhen using mass spectra data to confirm the structure of a substance extractedfrom willow bark and given the name salicylic acid. You can record the evidence asyou acquire it on the Information Sheet (Mass spectrum data). Rememberresearch chemists, when publishing their findings, must supply as much evidenceas possible to confirm the structure they propose for a compound even if, whenmore limited evidence is available, they already feel confident about the structure.Finding possible formulae1 Look first at Figure 1, the mass spectrum of salicylic acid. Measure therelative abundance of the six marked peaks. Record the mass andabundance of each peak in the appropriate box towards the bottomof the Information Sheet.100120Figure 1 The mass spectrum of salicylic acid80Intensity / %60402039 63 64 9213800 20 40 60 80 100 120 140 160Mass2 Decide which of these peaks gives the molecular mass of the compound.A computer database can list the possible molecular formulae that will fit this value.There can of course be a very large number. One limited database gives 38compounds for this molecular mass. Add this number to the Information Sheet.Using isotope peaks to establish theformulaThe number of possible compounds can be reduced by using the highresolutionmass spectrum facility. For the willow bark extract this gives anaccurate molecular mass of 138.0317. In the same database there are only twocompounds with this value: they are C 2H 7ON 4Cl and C 7H 6O 3. Add these possiblemolecular formulae to the Information Sheet.Naturally occurring carbon consists of a mixture of isotopes. Most carbon is 12 C,but 13 C is present as 1.1% of the sample. If the active chemical in the extractcontains one carbon atom in its molecule, the molecular ion peak at a mass Mshould be accompanied by another peak at M+1 with approximately 1.1% theintensity of the molecular ion peak. Two carbons will give rise to an M+1 peak ofapproximately 2.2% relative intensity, and so on.This means that for one carbon atom, the ratio of the intensities of M : M+1peaks will be 98.9 : 1.1; for two carbon atoms the ratio will be 97.8 : 2.2, and so on.144AS LEVEL„ Salters Advanced Chemistry 2000 – see Copyright restrictions
Page 1 and 2: WM1The origins anddevelopment of th
Page 4 and 5: THE ORIGINS AND DEVELOPMENT OF THE
Page 6 and 7: WM2Extraction of salicylicacidIn th
Page 8 and 9: WM3Investigating thechemistry of th
Page 12 and 13: INTERPRETATION OF THE MASS SPECTRUM
Page 14 and 15: WM5.1A preparation of aspirinThis a
Page 16 and 17: USING SPECTROSCOPYWM5.2100908070100
Page 18 and 19: AN ASPIRIN ASSAYWM68 Calculate the
Page 20 and 21: WHICH PRODUCT SHOULD A PHARMACEUTIC
Page 22 and 23: WHICH PRODUCT SHOULD A PHARMACEUTIC
Page 24: WM9Check your notes onWhat’s in a

Activities - Benjamin-Mills

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?