Nokea
Which subatomic particle can always be used to identify an atom?
- A. Protons
- B. Neutrons
- C. Electrons
- D. None of the above
Correct Answer: A
Rationale: The correct answer is A: Protons. Protons are positively charged subatomic particles found in the nucleus of an atom. The number of protons in an atom's nucleus determines the element's identity. While neutrons and electrons are also essential components of an atom, it is the number of protons that uniquely identifies the element. Therefore, protons can always be used to identify an atom.
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What does the term 'atomic number' represent?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number represents the number of protons in the nucleus of an atom. This number uniquely identifies an element and determines its placement in the periodic table. The number of neutrons and electrons can vary among different isotopes of an element, but the number of protons remains constant, defining the element's atomic number. Therefore, the correct answer is the number of protons (Choice B).
When propane is reacted in the presence of oxygen gas, the products of this combustion reaction are:
- A. C + H2
- B. CH2 + H2O
- C. CO2 + H2
- D. CO2 + H2O
Correct Answer: D
Rationale: When propane undergoes combustion in the presence of oxygen, it forms carbon dioxide (CO2) and water (H2O). The balanced chemical equation for this reaction is: C3H8 + 5O2 -> 3CO2 + 4H2O. This means that three molecules of carbon dioxide and four molecules of water are produced when one molecule of propane reacts with five molecules of oxygen. Therefore, option D (CO2 + H2O) is the correct answer.
Which of the following statements is most accurate regarding the compound 2Hâ‚‚O?
- A. 2Hâ‚‚O has a total of 2 hydrogen atoms.
- B. 2Hâ‚‚O represents two water molecules.
- C. Hâ‚‚O represents two water molecules.
- D. None of the above.
Correct Answer: B
Rationale: The chemical formula 2Hâ‚‚O represents two water molecules. Each water molecule (Hâ‚‚O) consists of 2 hydrogen atoms and 1 oxygen atom. Therefore, 2Hâ‚‚O denotes two separate water molecules, making choice B the correct statement
What occurs to an atom that has a positive charge?
- A. Gained an electron.
- B. Lost an electron.
- C. Gained a proton.
- D. Lost a proton.
Correct Answer: B
Rationale: When an atom has a positive charge, it indicates that it has lost an electron. Electrons carry a negative charge, so the absence of an electron leads to a net positive charge for the atom. Gaining a proton or losing a proton would modify the atom's identity by changing its atomic number, but it would not directly result in a positive charge. Therefore, the correct response is that the atom lost an electron to acquire a positive charge.
What is the density of carbon tetrachloride if a flask weighing 345.8 g is filled with 225 mL of the liquid, and the total weight of the flask and liquid is 703.55 g?
- A. 1.59 g/mL
- B. 2.76 g/mL
- C. 1.4 g/mL
- D. None of the above
Correct Answer: A
Rationale: To find the density of carbon tetrachloride, we first need to determine the weight of the liquid only. The weight of the liquid can be calculated by subtracting the weight of the empty flask from the total weight of the flask and liquid: 703.55 g - 345.8 g = 357.75 g. Now, using the volume of the liquid (225 mL) and its weight (357.75 g), we can calculate the density: Density = Mass/Volume = 357.75 g / 225 mL ĉ� 1.59 g/mL. Therefore, the correct answer is A, 1.59 g/mL.