It’s been nearly two months since I started my second year of Bromley College, and I’m finally back in the thick of the action! Since being back homework and studies have taken up much of my time, as well as finalising my UCAS form and sending it off (finally) on the 22nd of October. As to date, I have heard back from three of the four institutes I have applied to. One university, giving me an offer within two days of receiving my UCAS form (which I was utterly shocked about!). I have also had offers for interviews, which has quickly become the one of scariest concepts ever, only narrowly beaten by taking those brave steps into the exam hall, to take those dreaded exams!
With the spare time, I have had, I’ve dedicated it to my old student ambassador role. Such as being part of a college focus group, meeting with our college’s principle, Sam Parrett, to talk about changes to Bromley College. I have also recently, been re-elected to be class representation, however this year I got my dream role of repping for chemistry! The year before, I had been repping for biology. So far I have attended only one rep meeting, and have another coming up in the next few weeks.
Another aspect of being back in the swing of things is even more practical experiment. Practicals have been coming thick and fast in my second year. As with each new aspect of chemistry we study, the knowledge we learn is backed up with a simple demonstration of said aspect in action.
So far, we have covered reactions in aromatic and carbonyl compounds; now have moved on to carboxyl compounds and their reactions, and most recently, the study of amines.
We performed some basic tests on the carboxyl compounds ethanoic acid, investigating its solubility with water and the pH of the resulting solution. After concluding that carboxyl compounds are highly soluble in water and result in an acidic solution, we then went about testing the acidic strength of the carboxyl group, by testing it reacting it with sodium carbonate to see if it was strong enough to displace the CO3 and produce carbon dioxide. Finally in our investigation of glacial ethanoic acid, we investigated its formation of salt, via neutralisation. We added small amounts of sodium hydroxide to the acid, testing its pH and its ability to produce carbon dioxide from sodium carbonate. We saw that with each addition of sodium hydroxide, the resulting solution increased in pH and was less able to react with sodium carbonate to produce carbon dioxide.
In a later experiment, we also prepared the organic product, aspirin, from its constituents, ethanoic anhydride (also known as acetic anhydride) and salicylic acid, with phosphoric acid catalyst. We heated this mixture under reflux in a water bath. After heating we added a little distilled water to the reaction mixture, before pouring the synthesised aspirin and water mixture into a breaker of distilled water, to crystallise out the insoluble aspirin. After we had synthesised the aspirin we then carried out steps to purify it. We used the process of vacuum filtration and recrystalisation, using a water solvent, to gain reasonably pure crystals of aspirin. After this we then used a melting point tube with a thermometer and a capillary tube of our aspirin to measure the boiling point of our aspirin.
Most recently we have begun our studies of amine compounds, as we our carboxylic compounds. We preformed some basic investigative tests on them, for this test we studied the reactions of butyl-amine, ethyl 4-aminobezoate and ammonia. We tested all three compounds solubility in water and the resulting pH of the solutions. We concluded that, of butyl-amine, and ammonia were readily soluble in water, where as ethyl 4-aminobezoate was not, and required heating to dissolve. We also concluded that all three compounds resulted in basic solutions, with of butyl-amine and ammonia, having a pH of around 10, whereas ethyl 4-aminobezoate had a pH of around 8.5. We then tested the compounds ability to form salts, we added to a small amount of each amine, hydrochloric acid, drop wise and then smelt the solution, testing to see if the odours disappeared.
We then moved on to the formation of azo dyes using aromatic amines. In the formation of the dyes we proved that azo dyes can only be formed from aromatic amines, (in our case ethyl 4-aminobenzoate), by performing the experiment, using an aliphatic amine, butylamine, and water, as a control. We placed three separate beakers full our experimental solutions we were testing on our bench, and added 10 cm3 of aqueous sodium nitrate. Whilst letting the mixture stand, we prepared our naphthalene-2-ol (already in sodium hydroxide) by mixing it with cold water. We then added around 20cm3 of naphthalene-2-ol to each of the mixtures and watching as the colour of the azo dye instantly formed, in the ethyl 4-aminobenzoate beaker, whilst the aliphatic amine produced a thick precipitate, and the water did not change. Then using our formed azo dye, we each took a few small scraps of fabric and placed them into the mixture, before pulling them out and allowing them to dry on watch-glasses, to prove that azo dyes could be used to dye fabrics.
Our studies then turned to other types of nitrogen containing compounds, amino acids and proteins. We preformed more basic experimental tests on these compounds. In our tests we used glycine, glutamic acid, as well as casein hydrolysate (free amino acids found in milk). We started by testing their acidity and basicity, by adding small quantities of sodium hydroxide to each of the compounds, and then repeating with hydrochloric acid and noting down their change in pH of each compound, as the solutions were added. We also preformed a biuret test, a test common to many biologists! We added equal volumes of our amino acids to sodium hydroxide followed by 1 drop of 0.1M copper(II) sulphate, looking for the present of a purple precipitate if the compound was indeed an amino acid (or a protein), sadly we did not manage to take any photo graphs of the precipitate formed.
We have most recently moved on to addition and condensation polymers, before we broke up for half term. We had a very informal lab session, where we were allowed to ‘play’ with polyamides (forming and colouring nylon 6,6,) and cross-linked polymers. In the formation of nylon 6,6, we took a very small beaker and placed a small amount of the acid, 1,6-hexanedioic acid in the bottom, and at room temperature we added drop-wise the amine, 1,6-hexanadiamine until we saw an interface form, at this point we took tweezers and pinched the interface and carefully pulled it forming the nylon thread and wound it around a test tube. Next we moved on with forming our crossed-linked polymer, we took 20 cm3 of standard school grade PVC glue, and added 10 cm3 of borat, and mixed the solution with a glass rod, I was transported back to my childhood days as the mixture before me turned into horrible (colored by food coloring) slime! It was one of the best ways to end our first term of the year!
In physics we have covered a lot in the last few weeks, he have covered oscillations and SHM, and performing various experiments, such as, investigating the effect of spring constant on the time period and speed on oscillations, and various experiments on the effect of resistive forces on oscillation and the effect of damping. Our studies then moved onto fields, we have been learning about gravitational fields, unfortunately we only managed to perform one experiment estimating the acceleration of falling objects. In this experiment, we took a weighted plate, attaching a 30 g mass of blue tack and dropping the plate through a light gate, taking various readings of the time it took for the plate to drop from a set height. We then preformed a few calculations to find the acceleration of the plate, and as we assumed there were no other forces acting on the plate, acceleration of g. Most recently, we have moved on to looking at electric fields, meaning we have had the chance to use a van der Graaff generator, and perform simple tasks involving static electricity.
In biology, we have moved onto the interesting biochemistry involved with photosynthesis, after spending the last 5 weeks studying ecology. This new topic meant we were able to perform some interesting experiments involving separation of chlorophyll using paper chromatography, and practicing a past ISA task, involving exploring the effect of ammonium hydroxide on the time taken for chloroplasts to decolorize DCPIP ( a blue dye that becomes colorless as it accepts electrons and becomes reduced).
So after a first busy half a term back at college, I am back in the swing of things.
