All MCAT Physical Resources
Example Questions
Example Question #1 : Ions And Isotopes
Which of the following atoms has the same number of neutrons as an atom of ?
In order to find the number of neutrons in an atom when givien isotopic notation, simply subtract the bottom number (atomic number or number of protons) from the top number (mass number or number of protons and neutrons). Doing this with the question atom reveals that it contains 28 neutrons. The only other atom that has this amount is .
Example Question #7 : Ions And Isotopes
Suppose 0.5 moles of each of the following atoms is dissolved in 500 mL of water: calcium, oxygen, chlorine, barium, and silver. Which of the following resulting reactions is possible?
Although it appears that one must know solubility rules to answer this question, that is not the case. All but one of the answer choices employs incorrect charges. The periodic table can be used to predict charges of common ions. They are as follows: , , , , and . Next, recognize that an ionic compound is formed from a cation (positive) and an anion (negative), and that the total positive charge must equal the total negative charge for a neutral compound. That leaves the reaction between silver and oxygen as the only possible choice.
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