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What is a combustion reaction?
- A. It is endothermic.
- B. It substitutes one element for another.
- C. It always shares electrons.
- D. It is a reaction that involves oxygen.
Correct Answer: D
Rationale: A combustion reaction is a type of chemical reaction that involves a substance reacting with oxygen gas to produce heat and light. This reaction is exothermic, releasing energy in the form of heat and light. The correct answer is D because combustion reactions specifically involve oxygen as a reactant, leading to the production of heat and light as byproducts.
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What is the density of a block on your desk that acts as a paperweight? The block measures 3cm by 4cm by 6cm and has a mass of 184.32g.
- A. 13.27 g/cm3
- B. 2.56 g/cm3
- C. 0.39 g/cm3
- D. None of the above.
Correct Answer: B
Rationale: To calculate density, you use the formula: Density = Mass/Volume. First, calculate the volume of the block by multiplying its dimensions: 3cm x 4cm x 6cm = 72 cm3. Next, divide the mass (184.32g) by the volume (72 cm3) to find the density. Density = 184.32g / 72 cm3 = 2.56 g/cm3. Therefore, the correct answer is B, with a density of 2.56 g/cm3.
What is the name of a reaction in which electrons are transferred from one atom to another?
- A. combustion reaction
- B. synthesis reaction
- C. redox reaction
- D. double-displacement reaction
Correct Answer: C
Rationale: A redox reaction, short for reduction-oxidation reaction, involves the transfer of electrons from one reactant to another. In these reactions, one substance is oxidized (loses electrons) while another is reduced (gains electrons). The term 'redox' comes from the simultaneous occurrence of reduction and oxidation reactions. Combustion reaction (choice A) involves a substance reacting with oxygen to produce heat and light, but it does not necessarily involve electron transfer. Synthesis reaction (choice B) involves the combination of two or more substances to form a new compound, with no mention of electron transfer. Double-displacement reaction (choice D) involves an exchange of ions between two compounds but does not specifically involve electron transfer between atoms. Therefore, option C, redox reaction, is the correct answer as it accurately describes the electron transfer process that occurs during such reactions.
Which of the following substances is most dense?
- A. A block of gold weighing 12g and having a volume of 4.6cm³
- B. A cube weighing 6g and having a volume of 0.91cm³
- C. A block weighing 143g and having a volume of 24.3cm³
- D. None of the above.
Correct Answer: B
Rationale: The correct answer is 'B: A cube weighing 6g and having a volume of 0.91cm³.' Density is calculated as mass divided by volume. For each option: A) 12g/4.6cm³ ≈ 2.61 g/cm³, B) 6g/0.91cm³ ≈ 6.59 g/cm³, C) 143g/24.3cm³ ≈ 5.88 g/cm³. Therefore, option B is the most dense with a density of approximately 6.59 g/cm³.
Which element has 13 protons, 13 electrons, and 14 neutrons?
- A. Fe
- B. Zr
- C. Al
- D. Not enough information
Correct Answer: C
Rationale: The element with 13 protons is Aluminum (Al), as the atomic number of an element is determined by the number of protons. The total number of protons and neutrons in an element's nucleus is known as the mass number. Given that the mystery element has 13 protons and 14 neutrons, it matches the characteristics of Aluminum, making it the correct answer.
What occurs to an atom with a negative charge?
- A. Gained an electron
- B. Lost an electron
- C. Gained a proton
- D. Lost a proton
Correct Answer: A
Rationale: When an atom has a negative charge, it means it has gained an electron. Electrons are negatively charged particles, so when an atom gains an electron, it becomes negatively charged. This process is known as gaining an electron to achieve stability through a full outer electron shell. Atoms gain or lose electrons to attain a stable electron configuration, typically following the octet rule. In this case, gaining an electron is the correct choice as it results in the atom having a negative charge.