Regents Chemistry 5 — Questions and Answers
Question 1: Which of the following describes a chemical property of iron?
- Iron is a solid at room temperature
- Iron has a density of 7.87 g/cm³
- Iron reacts with oxygen to form rust (Correct answer)
- Iron is a good conductor of electricity
Correct answer: Iron reacts with oxygen to form rust
The ability to rust (react with O₂ and H₂O to form Fe₂O₃·nH₂O) is a chemical property because it involves a change in chemical composition.
Question 2: According to Le Chatelier's Principle, increasing pressure on a gaseous equilibrium shifts the reaction toward:
- The side with fewer moles of gas (Correct answer)
- The side with more moles of gas
- Neither side; pressure has no effect
- The side with higher temperature
Correct answer: The side with fewer moles of gas
Increasing pressure shifts equilibrium toward the side that reduces pressure, which is the side with fewer moles of gas.
Question 3: What type of isomers have the same molecular formula and connectivity but differ in the spatial arrangement of atoms?
- Structural isomers
- Constitutional isomers
- Stereoisomers (Correct answer)
- Chain isomers
Correct answer: Stereoisomers
Stereoisomers (including enantiomers and diastereomers) share the same molecular formula and bond connectivity but differ in three-dimensional arrangement.
Question 4: Which of the following solutions is the most concentrated?
- 1.0 M NaCl
- 2.0 M NaCl (Correct answer)
- 0.5 M NaCl
- 1.5 M NaCl
Correct answer: 2.0 M NaCl
Molarity (M) measures moles of solute per liter of solution; 2.0 M has the most moles of NaCl per liter and is therefore most concentrated.
Question 5: What is the half-life of a radioactive isotope if 75% of a sample decays in 20 years?
- 5 years
- 10 years (Correct answer)
- 15 years
- 20 years
Correct answer: 10 years
After one half-life, 50% remains; after two half-lives, 25% remains (75% decayed). Two half-lives = 20 years, so one half-life = 10 years.
Question 6: Which property increases as you move down a group on the periodic table?
- Electronegativity
- Ionization energy
- Atomic radius (Correct answer)
- Electron affinity
Correct answer: Atomic radius
Atomic radius increases down a group because each successive element has an additional electron shell, increasing distance from the nucleus.
Question 7: A buffer solution resists changes in pH because it contains:
- A strong acid and its conjugate base
- A weak acid and its conjugate base (Correct answer)
- Two strong acids
- Pure water and a neutral salt
Correct answer: A weak acid and its conjugate base
A buffer consists of a weak acid and its conjugate base (or weak base and conjugate acid), which can neutralize added acids or bases.
Regents Chemistry 5
Which of the following describes a chemical property of iron?