A Chinese Soul, a Global Mind, Let Chemistry Study be Connected with the World: the Lecture on Sharing the Experience in Chemical Life
The picture shows the guide teacher, Ms. Chen Yi, and some of the students.
At 12:10, President Fan Zixuan presided over the lecture. First, he introduced the time, place and basic information of the Royal Society of Chemistry Nova Challenge, the British Chemical Olympiad and the American Chemical Olympiad.
Same as last year, this year's test is still bilingual, so it's still quite a big challenge for NFLS students though who are usually good at English. In the United Kingdom, the United States Chemical Olympiad is done by individual students, so for our students, to improve their knowledge of chemistry is very important.
Next, we invited Zhou Pei, who had a thorough analysis of the King's test questions, to explain the idea of solving the problem. According to the conditions of the subject, Zhou Pei listed the relevant knowledge points and examination points, that got the consistent praise from other students.
Question: when the aqueous solution of potassium dichromate (VI) acidified with hydrogen peroxide was treated with hydrogen peroxide and then treated with diethyl ether, two layers of potassium dichromate were formed. The upper layer of organic layer contains blue compounds with the chemical formula CrO5, the structure of it is as follows:
the result of the reaction: Cr2O72– + 4H2O2 + 2H+→ 2CrO5 + 5H2O
as for this reaction, which of the following is correct?
A, potassium dichromate (VI) is oxidized to CrO5
B, hydrogen peroxide reduced
The answer is C.
Let's take a look at the options. By comparing the options, it is not difficult to find that this question is just a test? The mechanism and process of the reaction. This reaction has been mentioned in the chapter on hydrogen peroxide property in Inorganic Chemistry with blue cover, but it is a strange reaction for many students. So, the first thing we need to do is to compare the structure of the main reactants and products, and extrapolate what happens in the process of transformation through the differences between the two. We compared the structure of dichromate with that of chromium peroxide.
We will notice that in dichromate and chromium peroxides, chromium is connected to six bonds, which are six valences. This shows that the valence of chromium does not change before and after the total change. Chromium peroxide contains two superoxide bonds, which must come from hydrogen peroxide in the reactants. Therefore, it is concluded that there is no change in the valence state of elements in this process, and this reaction is not an oxidation-reduction reaction. We look again at the similarities between the two. We note that both of them contain chromium-oxygen double bonds, while hydrogen peroxide only loses hydrogen before and after the reaction, and the main superoxide bond still exists.
From these clues, we can venture to speculate that this is a substitution reaction, that peroxide groups replace the original oxygen in potassium dichromate. In dichromate ion, chromium is a positive six valences, with a large number of electrons lost and a high oxidation number. Therefore, it is very positive and prone to nuclear substitution reaction. So the nreagent is hydrogen peroxide, which is nucleophilic through the lone pair of electrons in the oxygen. Therefore, the reaction mechanism is not difficult to write down.
------ Part of it is from the analysis of the British king's Test prepared by Zhou Pei
After that, we invited former vice-president Wang Xicun to share his experience.
In USCHO (American Chemical Competition),there were 5 major questions, which might involve elements, analysis, electrochemistry, kinetics, thermodynamics, structure and organic and other directions. The internal contact in the questions is close, so when you meet the topic that requires thinking, try to do it until the end, you can get a lot of points. Do not get stuck, but maintain a stable state of mind, you can consider changing a question to continue. Organic reaction process is relatively simple, you can get a lot of points, I recommend doing it first. Note that IR (infrared spectrum), NMR (nuclear magnetic resonance) and other instruments in the organic topic requirements are relatively high, it is recommended to study them before the examination, If you can’t figure out the answers, do not waste of time doing them, the missing scores won’t affect you very much in the later questions.
As for time arrangement, I feel it very abundant, when I finished there was still have half an hour or so, but in order to guarantee the accuracy of quantitative question, I recommend to do common and qualitative question first, for quantitative questions, write down problem numbers and do them last, you must guarantee accurate calculation for the sake of a convenient check.
As for time arrangement, I feel it very abundant, when I finished there was still have half an hour or so, but in order to guarantee the accuracy of quantitative question, I recommend to do common and qualitative question first, for quantitative questions, write down problem numbers and do them last, you must guarantee accurate calculation for the sake of a convenient check.Then we entered the simulation session, the students discussed with each other heatedly, learned skills from each other, trained team cooperation ability,meanwhile learned a lot of new chemistry knowledge, they all had very deep feelings.
Through this activity held by the club,I learned a lot about chemistry competition that take place at home or abroad.I benefited a lot from the experience of the senior students.The quality of several exercises was very high. The analysis of inorganic reaction from the perspective of organic reaction mechanism provides me with a new angle of view to solve the problem. Thank you, all our alumni, this event really enriched my knowledge.
---Wang YizheThe activities of the Chemical Life Club were rather good. For me, this new member, I have seen a lot of winning experiences of the big guys, who had a great passion for chemistry, to solve the problem that I will not be able to solve at the lightening speed. To sum up ---- it inspired me to study chemistry harder, the community is very friendly, love you all.
-------- Yang Yi Jingjing
The lecture of Chemical Life Club was successfully completed. Thank the guidance of Teacher Chen, as well as Teacher Liu and Teacher Wang who work in the lab for their help.