Nokea
Which type of reaction is exemplified by the chemical equation Cr + Fe(NOÄ‚�)Ä‚‚ Ć’ Fe + Cr(NOÄ‚�)Ä‚�?
- A. Single replacement
- B. Decomposition
- C. Double replacement
- D. Combustion
Correct Answer: A
Rationale: The given chemical equation represents a single replacement reaction. In this type of reaction, one element displaces another element in a compound. In the provided equation, chromium (Cr) replaces iron (Fe) in the compound Fe(NOÄ‚�)Ä‚‚, resulting in the formation of Fe and Cr(NOÄ‚�)Ä‚�. Single replacement reactions involve the substitution of one element for another in a compound, which is precisely demonstrated in this scenario. Therefore, the correct classification for this reaction is a single replacement reaction.
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Which type of bond involves atoms gaining or losing electrons?
- A. Ionic
- B. Covalent
- C. Both
- D. Neither
Correct Answer: A
Rationale: Ionic bonds involve the transfer of electrons between atoms, leading to one atom gaining electrons (becoming negatively charged) while the other loses electrons (becoming positively charged). This results in the formation of ions that are held together by electrostatic forces, creating an ionic bond. In a covalent bond, atoms share electrons rather than gaining or losing them, making option A, 'Ionic,' the correct answer to this question. Therefore, the correct answer is 'Ionic,' as it specifically involves gaining or losing electrons to form a bond.
What is the density of iron when 28.5g of iron shot is added to a graduated cylinder containing 45.5mL of water, causing the water level to rise to the 49.1mL mark?
- A. 0.63 g/mL
- B. 7.92 g/mL
- C. 0.58 g/mL
- D. None of the above
Correct Answer: B
Rationale: To determine the density of iron, we use the formula: Density = Mass / Volume. The mass of the iron is given as 28.5g. The volume of water displaced by the iron is the final volume (49.1mL) minus the initial volume (45.5mL), resulting in 3.6mL. Therefore, the density of iron can be calculated by dividing the mass of iron (28.5g) by the volume of water displaced (3.6mL), giving us 7.92 g/mL. Therefore, choice B, 7.92 g/mL, is the correct answer.
What does carbonic acid become within the human body?
- A. Digests food
- B. Kills viruses
- C. Maintains pH of blood
- D. Grows hair
Correct Answer: C
Rationale: Carbonic acid, formed when carbon dioxide dissolves in water, plays a crucial role in maintaining the pH balance of the blood. It acts as a buffer to prevent drastic changes in blood pH, which is vital for the body's proper functioning. Carbonic acid does not digest food, kill viruses, or contribute to hair growth. Therefore, options A, B, and D are incorrect roles of carbonic acid within the human body, making maintaining the pH of blood (Option C) the correct answer.
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 atomic number?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number is the number of protons in an atom's nucleus. It uniquely identifies an element and determines its chemical properties. The number of neutrons and electrons can vary in an atom, but the number of protons remains constant for a specific element. Therefore, the correct answer is the 'Number of protons' (Choice B).