My teacher last year in General Chemistry was really great. She was highly organized, always prepared for class, approachable and fair. Chemistry is such a hard class that she really helped me get through it.
My Organic teacher is another story. She is a good lecturer but seems to be preparing her lecture in class some of the time. No one is ever quite sure when the assignments are due or what she wants of us. There is in my mind also a question of fairness.
Would you comment on my answers to three questions that were marked wrong? I know she will not be happy with me questioning her grading decisions. Also, maybe my answers are totally wrong and I am wrong.
The primary question is -
Criticize the following techniques:
a. A reflux is conducted with a stopper in the top of the condenser.
My answer: If a stoper is placed in the top of the condenser, the vapors cannot rise properly in the inner tube of the reflux condenser.
She wanted it mentioned that an explosion could happen.
c. No water hoses are attached to the condenser during a reflux.
My answer: The vapors in the condenser will not condense if there is no cooling water being run into the cooling tube.
She has a question mark on "run into the cooling tube." I don't know what her objection to that one is.
e. To save money, you decide to save your boiling stones for another experiment.
My answer: Omitting the boiling stones will not save money because it can wear and break the flask.
She said I should have interpreted it that not enough boiling stones were used rather than none were used.
This is probably not the kind of thing you would like to get get involved in but I'm thinking about dropping the class because of my perceptions of the teacher. I would greatly appreciate your advice on this, even if I'm wrong.
Thanks from Sheryl
Drop the class IF you think you will have a better alternative in the future. Sometimes in college you wont have a choice.
It is your money, and you ought to get your money's worth...If you have a better choice ahead.
a. The reflux goes between the pot and and the condenser for one thing. It is not clear as to how rubber stoppers are used in your lab. I would interpret that as a one-hole stopper being used. If the system is closed, then yes pressure will build up and something will have to give, i.e. blow apart. The setup should be pot(flask) -> reflux tube -> condenser -> receiver which is open to the atmosphere.
c. The condeser is really a cooling jacket around the vapor tube. Say that water going through that.
e. I interpret saving boiling stones as dumping them out of the flask and reusing them. I don't know why you would say that they would wear and break the flask. As to there not being enough boiling stones to reuse, I could not respond to that. I do not know how many were used in the first place. Can't tell from your information. In general reusing boiling stones is possible. But they could be contaminated by previous material. They should be washed with a volatile solvent and dried. Boiling stones work because they have little bubbles of air on them in the nooks and crannies of the stones when they are dumped into the liquid. These little bubbles provide surface for the liquid to transistion to the gas phase. The bubbles quickly become bubbles of vapor. The air has boiled away. Reusing boiling stones in the same flask after cooling could present a little problem. Let's say there is still liquid left in and the stones are still in the liquid. When the flask cools down the little bubbles that were on the surface of the stones are now just vapor of the whatever was being distilled. When it cools, the vapor bubbles will condense. There will no more bubbles on the surface. They're gone. If fresh liquid to be distilled is added and reheated. The boiling stones at first will be ineffective. It will bump and potentially boil over until new bubbles are reestablished on the surface. That is why the stones need to be dried first to get air back on and into the stones.
Your life path will be full of good people and not-so-good people. Embrace the good ones. You will not be able to avoid all of the not-so-good, you will have to learn on to deal with them in order to be fully successful.
a. A reflux is conducted with a stopper in the top of the condenser.
My answer: If a stoper is placed in the top of the condenser, the vapors cannot rise properly in the inner tube of the reflux condenser.
She wanted it mentioned that an explosion could happen.
Explosion is the firt thing that comes to my mind. Had I been grading your answer I would have given no credit for your answer.
c. No water hoses are attached to the condenser during a reflux.
My answer: The vapors in the condenser will not condense if there is no cooling water being run into the cooling tube.
She has a question mark on "run into the cooling tube." I don't know what her objection to that one is.
What you say is partially correct, IF (and only IF) the cooloing water to the condenser "runs in correctly"; however, the answer misses the mark. True, the vapors will not cool and condense; BUT, they will be lost to the system as they evaporate and move out the top of the reflux condenser. On the "question mark part", I suspect your teacher thinks you think that the cooling water "runs into the tube of vapors, itself" when in reality water runs into a jacket that is placed "around the cooling tube." It isn't clear from your description where the water runs. And that is the reason you lost credit for this entire answer. I don't know how much this question was worth on the exam. I MIGHT (notice might and not would) think about giving partial credit, but since it misses the mark, partial credit from me would be no more than 10 or 15%; i.e., on a 10 point question, I MIGHT think about giving 1 or 1-1/2 points. 2 pts max.
e. To save money, you decide to save your boiling stones for another experiment.
My answer: Omitting the boiling stones will not save money because it can wear and break the flask.
She said I should have interpreted it that not enough boiling stones were used rather than none were used.
I would have given no credit for your answer because it doesn't address the question. The questions says "save the boiling stones for another experiment" and that means to me we run an experiment, remove the boiling stones, let them dry, and reuse them in the next experiment. I don't get your answer about wear and tear on the flask (and I don't think it addresses the question) BUT I don't get the interpretation from the teacher, either. From my perspective, I don't see anything to make me think we are using fewer stones. The question clearly states, to me, that we save the boiling stones (all of them) for another experiment.
I hope this helps you decide what you want to do about the exam. As for dropping the class, Bob Pursley's advice may be the best; i.e., it depends upon the alternatives you have. Personally, however, I think you must learn to deal with all kinds of people in life. I had VERY good teachers and I had VERY POOR teachers (bottom of the barrel poor) but I stuck with them. It meant I had to dig a little harder myself and I wasn't always pleased with the results. But somehow we manage to overcome most of life's obstacles and move on. In the end the decision is yours to make. If you stay in the course, my recommendation is that you read and reread the questions, then give clear and concise answers to the questions. I hope this helps.
Thanks for the help. Looks like things aren't as bad as I thought with the teacher. Her native language is not English so there could be a communication problem with that. She is a good lecturer and I do enjoy her lectures.
Sheryl