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Quiz: Foundations of Chemistry

Test your understanding of matter, measurement, and scientific skills with these review questions.

1. Which of the following is a compound?

  1. Oxygen gas (\(\ce{O2}\))
  2. Table salt (\(\ce{NaCl}\))
  3. Bronze (a mixture of copper and tin)
  4. Pure gold (\(\ce{Au}\))
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The correct answer is B. Table salt (\(\ce{NaCl}\)) is a compound because it is a pure substance composed of two different elements (sodium and chlorine) chemically bonded in a fixed 1:1 ratio. Oxygen gas (A) is an element (only one type of atom). Bronze (C) is a mixture (alloy), not a compound. Gold (D) is an element.

Concept Tested: Compounds

2. A student dissolves sugar in warm water. The solution is clear and the sugar seems to disappear. Which best describes this process?

  1. A physical change, because no new substance is formed
  2. A chemical change, because the sugar disappeared
  3. A chemical change, because energy was involved
  4. Neither a physical nor a chemical change
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The correct answer is A. Dissolving sugar in water is a physical change because the sugar molecules remain intact — they are simply dispersed among the water molecules. No new substance is formed. The sugar can be recovered by evaporating the water. Option B is incorrect because disappearing from view does not mean a new substance formed. Option C is incorrect because energy involvement alone does not make a change chemical.

Concept Tested: Physical Changes

3. What is the correct number of significant figures in the measurement 0.004070 g?

  1. 3
  2. 4
  3. 5
  4. 7
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The correct answer is B. The measurement 0.004070 has four significant figures: 4, 0, 7, and the trailing 0. The three leading zeros (before the 4) are not significant — they only serve as placeholders. The zero between 4 and 7 is significant because it falls between nonzero digits. The trailing zero after 7 is significant because it follows a decimal point.

Concept Tested: Significant Figures

4. Which statement correctly describes the difference between accuracy and precision?

  1. Accuracy means measurements are close to each other; precision means they are close to the true value
  2. Accuracy and precision mean the same thing in scientific measurement
  3. Accuracy refers to how close measurements are to the true value; precision refers to how close repeated measurements are to each other
  4. Precision can only be determined if the true value is known
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The correct answer is C. Accuracy describes how close a measurement is to the accepted (true) value, while precision describes how close repeated measurements are to one another. Option A reverses the two definitions. Option B is incorrect because they are distinct concepts. Option D is incorrect because precision depends only on the consistency of repeated measurements and does not require knowledge of the true value.

Concept Tested: Accuracy and Precision

5. A sample of matter has a non-uniform composition and can be physically separated into its components. How should this sample be classified?

  1. Element
  2. Compound
  3. Homogeneous mixture
  4. Heterogeneous mixture
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The correct answer is D. A heterogeneous mixture has a non-uniform composition — you can see or detect different regions within the sample — and its components can be separated by physical means such as filtration or hand sorting. A homogeneous mixture (C) would have uniform composition throughout. Elements (A) and compounds (B) are pure substances that cannot be separated by physical means.

Concept Tested: Mixtures

6. Convert 2.50 hours to seconds using dimensional analysis.

  1. 150 s
  2. 1,500 s
  3. 9,000 s
  4. 9,000,000 s
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The correct answer is C. Using dimensional analysis: \(2.50 \text{ hr} \times \frac{60 \text{ min}}{1 \text{ hr}} \times \frac{60 \text{ s}}{1 \text{ min}} = 9{,}000 \text{ s}\). The hours cancel with hours, minutes cancel with minutes, leaving seconds as the final unit. Option A incorrectly divides by 60 once. Option B only converts to minutes (150 min) and does not complete the second conversion. Option D adds extra factors of 1,000.

Concept Tested: Dimensional Analysis

7. A metal sample has a mass of 54.0 g and a volume of 20.0 cm\(^3\). What is its density, and which metal does this most likely represent?

  1. 2.70 g/cm\(^3\) — aluminum
  2. 7.87 g/cm\(^3\) — iron
  3. 1.08 g/cm\(^3\) — water
  4. 19.3 g/cm\(^3\) — gold
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The correct answer is A. Density is calculated as \(d = m/V = 54.0 \text{ g} / 20.0 \text{ cm}^3 = 2.70 \text{ g/cm}^3\). Comparing this to the known density values in the chapter, 2.70 g/cm\(^3\) matches aluminum. Iron (B) has a density of 7.87 g/cm\(^3\), water (C) is 1.00 g/cm\(^3\), and gold (D) is 19.3 g/cm\(^3\).

Concept Tested: Density

8. Which of the following is the correct representation of 0.000482 in scientific notation?

  1. \(48.2 \times 10^{-5}\)
  2. \(4.82 \times 10^{-4}\)
  3. \(4.82 \times 10^{4}\)
  4. \(0.482 \times 10^{-3}\)
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The correct answer is B. In proper scientific notation, the coefficient must be between 1 and 10. Moving the decimal point four places to the right gives 4.82, so the exponent is \(-4\). Option A has a coefficient greater than 10. Option C uses a positive exponent, which would represent 48,200. Option D has a coefficient less than 1.

Concept Tested: Scientific Notation

9. In a sealed container, magnesium ribbon is burned in air. What happens to the total mass inside the container?

  1. The total mass increases because new products are formed
  2. The total mass decreases because gases are produced
  3. The total mass remains the same
  4. The total mass increases because energy is released
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The correct answer is C. According to the law of conservation of mass, in any chemical reaction, the total mass of the reactants equals the total mass of the products. Since the container is sealed, no matter enters or leaves. The magnesium reacts with oxygen to form magnesium oxide, but the total mass inside the container does not change. Options A and D are incorrect because mass is conserved regardless of product formation or energy changes. Option B is incorrect because the sealed container retains all gases.

Concept Tested: Conservation Laws

10. Which observation provides the strongest evidence that a chemical change has occurred?

  1. A substance changes from solid to liquid when heated
  2. A solution changes color when a powder is dissolved in it
  3. Bubbles of gas form and the temperature rises when two solutions are mixed
  4. A substance is ground into a fine powder
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The correct answer is C. Gas production combined with a temperature change provides strong evidence that a chemical reaction has occurred, indicating new substances are being formed and energy is being released or absorbed. Option A describes melting, which is a physical change. Option B could be either physical or chemical — dissolving a colored powder is often just a physical change. Option D is a physical change (changing shape/size does not alter chemical identity).

Concept Tested: Chemical Changes