General Chemistry at Penn State
CHEM 110
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HOW SHOW WORK FOR NON-NUMERICAL MULTIPLE CHOICE HOMEWORK PROBLEMS |
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You are required to “show your work” for all of the homework problems in order to receive credit for doing them. For some multiple choice problems, it looks like all you can do is select the correct answer. How do you show your work for a problem like that? Below is a question that falls into this category. Below the question, you will see an example of how you can “show your work” for this question
This method does require more effort, however, in the process of answering a question like this, you will get a chance to re-enforce the material. In addition, you may learn more from the problem, enabling you to do better on the exams.
SAMPLE QUESTION
X and Y are two species, each consisting of one nucleus and a number of electrons. The two species are found to contain the same number of protons, the same number of neutrons, and different numbers of electrons. Which of the following statements about X and Y is correct?
A. X and Y are both neutral atoms.
B. X and Y are isotopes of one another.
C. The two have different atomic numbers.
D. At least one of the species is an ion.
E. There is no answer above, since A–D are all incorrect.
ANSWER where you "show" your work.
Choice A must be false since the two species contain the same number of protons and different # of electrons. If one of them is neutral, the other would have to be charged if it had a different number of electrons from the other.
Choice B is false because X and Y have the same number of protons (so they are the same type of atom) AND the same number of neutrons. Isotopes are species that have the same number of protons, but different number of neutrons.
Choice C is false because the atomic number of a species is determined by the number of protons. Since both species have the same number of protons they must have the same atomic number.
Choice D is true: it was determined in Choice A that if one of the two was the neutral, the other must be charged (since they have differing numbers of electrons). In fact it is possible for both species to be charged.
Choice E is incorrect because Choice D is correct!