Tutor profile: Ben L.
Subject: Organic Chemistry
Would you expect phenol or para-nitrophenol to be more acid, and why?
The acidity in this case has to do with the stability of the conjugate base, which is what remains of the molecule once a proton is taken away. Having a nitro group on the benzene ring is electron withdrawing, and therefore an anion can be stabilized. Since para-nitrophenol will have the more stable conjugate base, it will be more acidic than phenol.
What temperature conditions should a reversible exothermic reaction be run under in order to maximize the yield?
Since the reaction is exothermic, heat is produced, and therefore heat can be thought of as one of the reaction products. Based on Le Chatleier's Principle, decreased the concentration of one of the reaction products should shift the reaction to the right, thus increasing the yield. Therefore, we should decrease the amount of heat by cooling the reaction.
An inflatable raft is floating in a swimming pool, and a crate is thrown off of the raft and into the pool. What happens to the water level in the pool? Does it increase, decrease, or remain the same?
The answer is, it depends on whether the crate sinks or floats. First, we can assume that it floats. While it is floating in the water, it displaces an amount of water which is equal to its own weight (this is based on Archimedes' principle). While it was in the raft, it made the raft heavier and caused the raft to also displace an additional amount of water equal to its own weight. So, whether the crate is on the raft or floating on its own, the amount of water it is responsible for displacing is the same, so there is no change in the water level. We can also consider the other possibility in which the crate sinks. Since it sinks, it displaces its own volume of water. While it was on the raft, it displaces an amount of water equal to its weight. Since it is more dense than water (it must be, if it sinks), it displaces more water when it is displacing water according to its weight rather than according to its volume. Therefore, it displaced more water while on the raft, and the water level must decrease when it is thrown off the raft.
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