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Where are protons held within an atom?
- A. Nucleus
- B. Orbitals
- C. Electron cloud
- D. None of the above
Correct Answer: A
Rationale: The correct answer is A: Nucleus. Protons are held in the nucleus, the central part of an atom where both protons and neutrons are located. Protons carry a positive charge and are specifically found within the nucleus. Orbitals and the electron cloud are regions where electrons are located surrounding the nucleus, not protons. Understanding the basic structure of an atom is fundamental in chemistry, where the nucleus serves as the core that contains the majority of the atom's mass and positive charge due to the presence of protons. This knowledge is crucial for grasping various chemical concepts and explaining the behavior of elements in chemical reactions.
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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 can be predicted by using the periodic table?
- A. The properties of each of the elements
- B. The charges of polyatomic ions
- C. The number of isotopes in each element
- D. The potential for the discovery of new elements
Correct Answer: A
Rationale: The periodic table is a fundamental tool in chemistry that organizes elements based on their properties. By using the periodic table, scientists can predict the properties of each element. The arrangement of elements in the table groups together elements with similar characteristics, allowing for the prediction of various properties such as reactivity, atomic size, and electronegativity. These predictions are possible because elements in the same group or period exhibit similar chemical behaviors. Therefore, the correct answer is A: The properties of each of the elements.
What is pH?
- A. The measure of concentration of H₃O⺠ions
- B. The measure of concentration of hydrogen ions
- C. The measure of concentration of Hâ‚‚O molecules
- D. None of the above
Correct Answer: A
Rationale: The correct answer is 'A: The measure of concentration of H₃O⺠ions.' pH is a measure of the concentration of hydronium ions (H₃Oâº) in a solution, indicating the acidity or alkalinity on a scale from 0 to 14. Values below 7 are acidic, 7 is neutral, and above 7 is alkaline/basic. Choice B is incorrect as pH specifically measures hydronium ions, not hydrogen atoms. Choice C refers to water (Hâ‚‚O), which is not directly related to pH measurement.
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.
Which subatomic particle does not contribute significantly to an atom's mass?
- A. Proton
- B. Neutron
- C. Electron
- D. All contribute to the atom's mass.
Correct Answer: C
Rationale: Electrons do not contribute significantly to an atom's mass. Protons and neutrons are much more massive than electrons and make up the majority of an atom's mass. Electrons have a very small mass compared to protons and neutrons, and their contribution to the total mass of an atom is considered negligible. Therefore, the correct answer is C, Electrons.