Nokea
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.
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What is the term for the reactant that is fully consumed by the reaction?
- A. limiting reactant
- B. reducing agent
- C. reaction intermediate
- D. reagent
Correct Answer: A
Rationale: The correct answer is 'limiting reactant.' In a chemical reaction, the limiting reactant is the substance that is entirely consumed when the reaction proceeds. It determines the extent of the reaction and limits the amount of product that can be formed. The other choices, such as 'reducing agent,' 'reaction intermediate,' and 'reagent,' do not specifically refer to the reactant that is fully consumed in the reaction.
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 type of reaction is represented by the equation KCl → K + Cl₂?
- A. Synthesis
- B. Decomposition
- C. Single replacement
- D. Double replacement
Correct Answer: B
Rationale: The reaction KCl → K + Cl2 is an example of a decomposition reaction. In a decomposition reaction, a compound breaks down into its constituent elements or simpler compounds. In this case, potassium chloride (KCl) decomposes into potassium (K) and chlorine gas (Cl2). Therefore, the correct answer is B, Decomposition.
What products are formed when methane undergoes combustion?
- A. CHâ‚„ and Oâ‚‚
- B. COâ‚‚ and Hâ‚‚O
- C. Both COâ‚‚ and Hâ‚‚O
- D. None of the above
Correct Answer: B
Rationale: When methane (CH₄) undergoes combustion with oxygen (O₂), the products formed are carbon dioxide (CO₂) and water (H₂O). The balanced chemical equation for this reaction is: CH₄ + 2O₂ → CO₂ + 2H₂O. Therefore, the correct answer is option B, CO₂ and H₂O. The combustion of methane is a common example of a hydrocarbon reacting with oxygen to produce carbon dioxide and water, releasing energy in the form of heat and light.
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.