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

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?

A. Seconds-long
B. Days-long
C. Years-long
D. Many years long

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. In which state of matter are particles packed tightly together in a fixed position?

A. Liquid
B. Solid
C. Gas
D. Plasma

Correct answer: B

Rationale: In a 'solid' state, particles are tightly packed in fixed positions, maintaining a definite shape and volume. This arrangement allows solids to maintain a rigid structure. Liquids have particles that are close together but can move past each other, giving them the ability to flow and take the shape of their container. Gases have particles that are far apart and move freely, leading to their ability to expand to fill any container. Plasma is an ionized gas where particles have high energy levels and are not packed tightly together, making it an uncommon state of matter on Earth.

3. At what temperature does water boil in °F?

A. 210°F
B. 212°F
C. 215°F
D. 220°F

Correct answer: B

Rationale: Water boils at 212°F under standard atmospheric pressure. This is the point at which water changes from a liquid to a gas phase. Choice A (210°F) is incorrect as it is below the boiling point of water. Choice C (215°F) and Choice D (220°F) are also incorrect as they are above the boiling point of water.

4. Which type of chemical reaction involves two ionic compounds where the reactants yield 'switched partners'?

A. Single replacement
B. Double replacement
C. Synthesis
D. Decomposition

Correct answer: B

Rationale: The correct answer is 'Double replacement.' In a double replacement reaction, two ionic compounds react by exchanging ions, resulting in the formation of two new compounds where the positive and negative ions have 'switched partners.' This type of reaction is characterized by the exchange of ions between the reactants. Choice A, 'Single replacement,' involves an element replacing another in a compound, not the exchange of partners like in the given scenario. Choice C, 'Synthesis,' is the combination of two or more substances to form a more complex product, not involving the exchange of partners. Choice D, 'Decomposition,' is the breakdown of a compound into simpler substances, which is different from the scenario described in the question.

5. How many electron pairs are shared to form a triple covalent bond?

A. 1
B. 2
C. 3
D. 4

Correct answer: C

Rationale: The correct answer is C. In a triple covalent bond, three pairs of electrons are shared between two atoms. This sharing results in a total of six electrons being shared, making the bond strong. Choice A (1) is incorrect because a single covalent bond involves the sharing of one pair of electrons. Choice B (2) is incorrect as a double covalent bond consists of the sharing of two pairs of electrons. Choice D (4) is incorrect because there are only three pairs of electrons shared in a triple covalent bond, not four.