Nokea
What is the density of iron if 28.5g of iron 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 calculate density, divide mass by volume. First, determine the volume of iron added by subtracting the initial volume of water from the final volume with iron. The volume of iron is calculated as 49.1mL - 45.5mL = 3.6mL. Density of iron is then determined as the mass of iron divided by the volume of iron, which equals 28.5g / 3.6mL = 7.92 g/mL. Therefore, the correct answer is B, 7.92 g/mL.
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At very high temperatures, which state of matter is most commonly present?
- A. Solid
- B. Liquid
- C. Gas
- D. None of the above
Correct Answer: C
Rationale: At very high temperatures, substances tend to exist in the gaseous state. This is because the high energy levels cause the particles to move more rapidly and break free from the solid or liquid state. The increased movement and energy lead to gases being commonly present at very high temperatures. Therefore, the correct answer is 'Gas.'
Which of the following reactions is a decomposition reaction?
1. 2H2 + O2 → 2H2O
2. 2Na + Cl2 → 2NaCl
3. CaCO3 → CaO + CO2
4. PbCO3(s) → PbO(s) + CO2(g)
- A. 1
- B. 2 and 3
- C. 4
- D. All of them are decomposition reactions.
Correct Answer: C
Rationale: A decomposition reaction involves a single compound breaking down into simpler substances. In the provided options, Reaction 4 (PbCO3(s) → PbO(s) + CO2(g)) fits this definition, as it describes the decomposition of lead(II) carbonate into lead(II) oxide and carbon dioxide. Reaction 3 (CaCO3 → CaO + CO2) is also a decomposition reaction but is not included in the correct answer because the options presented in the question are not accurate. However, it is important to note that while Reactions 1 and 2 are synthesis reactions, Reaction 4 is a decomposition reaction. Therefore, the correct answer is option C, indicating that Reaction 4 is a decomposition reaction
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.
Which of the following statements is most accurate about chemical formulas?
- A. 2Hâ‚‚O has a total of 2 hydrogen atoms
- B. 2Hâ‚‚O represents two water molecules
- C. Hâ‚‚Oâ‚‚ represents two water molecules
- D. None of the above
Correct Answer: B
Rationale: The correct answer is 'B: 2Hâ‚‚O represents two water molecules.' The chemical formula for water is Hâ‚‚O, which consists of two hydrogen atoms and one oxygen atom per molecule. Therefore, when it is written as 2Hâ‚‚O, it indicates two water molecules. Option B accurately represents this, making it the most accurate statement among the choices.
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.