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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.
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What is the mass of ethyl alcohol that exactly fills a 200.0 mL container?
- A. 157.8 g
- B. 253.49 g
- C. 0.0039 g
- D. None of the above
Correct Answer: A
Rationale: To determine the mass of ethyl alcohol that fills a 200.0 mL container, we use the formula: Mass = Volume x Density. Given that the density of ethyl alcohol is 0.789 g/mL, multiplying the volume (200.0 mL) by the density gives us 200.0 mL x 0.789 g/mL = 157.8 g. Therefore, the correct answer is A, 157.8 g, representing the mass of ethyl alcohol that exactly fills the 200.0 mL container.
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.
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.
How many oxygen atoms are in 2Oâ‚‚?
- A. 2
- B. 4
- C. 1
Correct Answer: B
Rationale: The chemical formula 2OÄ‚‚ represents two molecules of oxygen, where each molecule contains two oxygen atoms. To find the total number of oxygen atoms, you multiply the number of molecules (2) by the number of atoms in each molecule (2), which equals 4 oxygen atoms in total.
Which type of reaction is exemplified by the chemical equation KClO₃ → KCl + O₂?
- A. Single replacement
- B. Double replacement
- C. Combustion
- D. Decomposition
Correct Answer: D
Rationale: The chemical equation KClO₃ → KCl + O₂ represents a decomposition reaction. In a decomposition reaction, a single compound breaks down into two or more simpler substances. In this case, potassium chlorate (KClO₃) decomposes into potassium chloride (KCl) and oxygen gas (O₂). Therefore, the correct answer is D: Decomposition. This reaction is not a single replacement reaction (where one element replaces another in a compound), a double replacement reaction (where ions in two compounds exchange places), or a combustion reaction (which involves a substance reacting with oxygen to produce heat and light).