1. Sorted FAQs on Aspirin investigations

A. Synthesis & Properties
1. How much starting material to use?
2. How - from salicylic acid and ethanoic anhydride?
3. Which method is most efficient?
4. Is synthesis nucleophilic substitution? Nucleophile?
5. Finding optimum conditions?
6. Purpose of refluxing?
7. Phosphoric acid as catalyst
8. Use of phosphoric acid?
9. Use of HCl as catalyst
10.Reasons for low yield?
11.Methods to increase yield?
12.Theory behind recrystallisation?
13.Suitable solvents for recrystallisation?
14.Reasons for higher/lower M.Pt. after recrystallisation?
15.Purity check via M.Pt.?
16.B.Pt for pure aspirin?
17.M.Pt for pure aspirin?
18.Calculating theoretical yield
19.How to obtain soluble aspirin?
20.Why is M.Pt. of soluble aspirin different?
21.Industrial preparation of aspirin?
22.Melting point of aspirin tablet?
23.No solid product after filtration
24.Equation for decomposition in water
25.Use of iodine as locating agent for TLC
26.R_f value for aspirin
27.How to get aspirin to crystallise?
 
B. Direct titration
1. Effect of salicylic acid impurity on titration?
2. Stoichiometry of direct titration vs back titration?
3. What chemicals to use?
4. Procedure with NaOH?
5. Why no strong heating?
6. Reason for low titre value?
7. Removal of salicylic acid by fractional distillation?
8.% Purity from pH titration
9.Effect of solvent on titre values?
 
C. Back titration
1. Back vs direct titration - which gives highest % aspirin?
2. Why is back titration better?
3. Principles and methods of back titration?
4. What does hydrolysis do? Why back titration?
5. Why more reliable?
6. Stoichiometry for back titration vs direct titration?
7. Stoichiometry for back titration reactions?
8. Indicator colour change?
9.Stoichiometry of back titration vs direct titration?
10.How to calculate amount of pure aspirin to use in titration?
11.How long to hydrolyse?
12. Why not boil dry? Why back titration?
13.Effect of salicylic acid impurity?
14.Presence of other substances
15.Effect of lactose?
16.Effect of hydrolysis products on pH of equivalence point?
17.Effect of impurities?
18.Ideal NaOH concentration for titration?
19. How to dilute 1 M NaOH and standardise it?
20. How to standardise NaOH with KHP (K-hydrogen phthalate?
21. Why no indicator colour change?
22.Reasons for low burette reading?
23.pH Titration?
24. Difference between mass on packet and experiment?
25.Effect of starch in tablet on titration values?
26.Mass ASA in aspirin tablet by back titration
 
D. Colorimetry
1. Why not hydrolyse aspirin?
2. How much to hydrolyse?
3. Why use FeCl₃, KCl & HCl and how much?
4. How to treat hydrolysed aspirin solution?
5. Why is Fe(III) necessary?
6 .Need to add Fe(III) to hydrolysed solution?
7 .How to set up a calibration curve?
8. Concs. for calibration curve?
9. Suitable concs. for calibration curve?
10.Use of calibration graph?
11.Sensible absorption values for calibration curve?
12.Calibration curve - use of buffer?
13.How to deal with salicylic acid impurity?
14.Help with calculations
15.Help with calculations
16.Help with calculations
17.Calculating the error
18.How does it work using Cu²⁺?
19.Is a phenol group required for coloured complex?
20.Effect of urine colour on absorbance?
21.Changing transmission to absorbance
22.Why initially hydrolyse before adding Fe₃₊?
23.Solvent for colorimetry
 
E. Miscellaneous
1. Chromatography: Different R_f values from different brands?
2. Tablets: What else present?
3. Reaction of aspirin with hot permanganate?
4. Why ethanol as solvent for aspirin?
5. Purity - back titration, chromatography, M.Pt. etc?
6. Structure of iron(III) - salicylic acid complex?
7. Interpolation method for aspirin purity
8. Effect of ethanol as solvent?
9. Other pharmaceuticals to synthesise at A-level?
10.How to obtain soluble aspirin?
11.Why is pure aspirin not sold commercially?
12.Paracetamol titration: use of standardised solution?
13. Decomposition of aspirin by autocatalysis?
 
See also the tutorial on aspirin investigations

Recently Asked Questions

• 1. My advanced higher chemistry project is on tests distinguishing aldehydes and ketones. One of the methods to determine this is by using Schiff's Reagent. I was wondering if there is a non-complicated way of preparing the reagent or if I could just use a ready-made one. 2. Could you give me the procedure of how to prepare 2,4-dinitrophenylhydrazine? 3. Could you please help me with the procedure of distinguishing between aldehydes and ketones using 2,4- dinitrophenylhydrazine? On some websites it states that crystals are formed and on others I am told that the solution should turn orange resulting in the presence of a ketone. 091008

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updated: 07 August 2008