Sample Chemistry Regents Questions Information provided by Kaplan Test Prep

1. What is the mass number of an atom that contains 19 protons, 19 electrons, and 20 neutrons?
   1. 19
   2. 20
   3. 39
   4. 58
   
   
2. A radioactive element has a half-life of 2 days. Which fraction represents the amount of an original sample of this element remaining after 6 days?
   1. 1/8
   2. 1/2
   3. 1/3
   4. 1/4
   
   
3. At STP, potassium is classified as
   1. a metallic solid
   2. a molecular solid
   3. a network solid
   4. an ionic solid
   
   
4. A mixture of oxygen, nitrogen, and hydrogen gases exerts a total pressure of 740. mmHg at 0°C. The partial pressure of the oxygen is 200. mmHg and the partial pressure of the nitrogen is 400. mmHg. What is the partial pressure of the hydrogen gas in this mixture?
   1. 140. mmHg
   2. 200. mmHg
   3. 400. mmHg
   4. 740. mmHg
   
   
5. Which type of bond is formed between the two chlorine atoms in a chlorine molecule?
   1. polar covalent
   2. nonpolar covalent
   3. metallic
   4. ionic
   
   

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Answer Key

1. The correct answer is (C). Nucleons are the particles that reside in the nucleus and that would be only protons and neutrons.
2. The correct answer is (A). Six days constitutes three half-life (two days each) time periods which means three cycles of losing half of the material. That means 1/2 x 1/2 x 1/2, which equals 1/8 of the material remaining.
3. The correct answer is (A). At STP, potassium is neither a molecular solid nor an ionic solid, both of which require electron movement. This is not mentioned and so we must be dealing with the elemental potassium, which exists in metallic form.
4. The correct answer is (A). Dalton's Law of Partial Pressure says that each gas contributed to the total pressure in a mixture of gases. The total pressure in this question is 740 mmHg, with oxygen and nitrogen both contributing for a total of 600 mmHg, leaving 140 mmHg for the remaining gas, hydrogen.
5. The correct answer is (B). With the mostly equal distribution of the level 3 electrons after covalent bonding of the atoms, no clear separation of charge exists in the chlorine molecule, which creates a nonpolar covalent bond.