radioactive isotopes are frequently used in medicine what kind of half life would a medical isotope probably have
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HESI A2

Chemistry HESI A2 Practice Test

1. Radioactive isotopes are frequently used in medicine. What kind of half-life would a medical isotope probably have?

Correct answer: B

Rationale: Medical isotopes used in diagnosis and treatment need to have a relatively short half-life to minimize radiation exposure to patients. If the half-life were too long (such as many years) or even years-long, the radiation would persist for too long and could be harmful to the patient. Seconds-long half-lives would not provide enough time for the isotope to be effective. Days-long half-lives strike a balance between providing enough time for the isotope to be used effectively and minimizing radiation exposure.

2. How many electrons are in a neutral atom of neon?

Correct answer: B

Rationale: The atomic number of neon is 10, which represents the number of protons in its nucleus. In a neutral atom, the number of electrons is equal to the number of protons to maintain electrical neutrality. Therefore, a neutral atom of neon contains 10 electrons, matching the 10 protons within the nucleus. Choice A (9 electrons) is incorrect as it doesn't correspond to the atomic number of neon. Choices C (11 electrons) and D (12 electrons) are also incorrect as they do not align with the correct atomic number of neon.

3. What creates a dipole in a covalent bond?

Correct answer: A

Rationale: A dipole is created in a covalent bond when there is an unequal sharing of electrons between the atoms involved. This results in a partial positive charge on one atom and a partial negative charge on the other, leading to a separation of charges and the formation of a dipole. Choices B, C, and D are incorrect because a dipole is specifically formed due to unequal sharing of electrons, not equal sharing, exchange, or transfer of electrons in a covalent bond.

4. Balance this equation: Zn + HCl → ZnCl + H2.

Correct answer: C

Rationale: The given unbalanced equation is Zn + HCl → ZnCl + H2. To balance it, we need to have equal atoms on both sides of the equation. The balanced equation is 2Zn + 2HCl → 2ZnCl + H2. This balanced equation shows that two atoms of Zn combine with two molecules of HCl to form two molecules of ZnCl and one molecule of H2. Choice A is incorrect because it does not balance the equation. Choice B is incorrect as it does not have the same number of atoms on both sides. Choice D is incorrect because it does not balance the equation properly, resulting in an unequal number of atoms on both sides.

5. What is the product of the decomposition of water?

Correct answer: A

Rationale: The correct answer is A: Hydrogen and oxygen. When water undergoes decomposition, it breaks down into hydrogen and oxygen gases through a process known as electrolysis. This reaction is represented by 2H₂O → 2H₂ + O₂. Choice B, carbon dioxide, is incorrect as it is not a product of water decomposition. Choice C, nitrogen and hydrogen, is incorrect as water decomposes into hydrogen and oxygen, not nitrogen. Choice D, methane, is incorrect as methane is not a product of water decomposition.

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