What this section covers: Matter, Chemical equations and reactions, The periodic table, Atomic structure, Nuclear chemistry, Chemical bonding.
10 free practice questions
Click an answer: you see at once whether it is right, with the explanation.
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Question 1Which of the following is a chemical change?
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Answer: A — Iron rusting.
Rusting forms a new substance (iron oxide), so it is a chemical change. Melting, boiling and dissolving change the state or mixing of a substance without changing its chemical identity.
Checked against: OpenStax Chemistry 2e, 1.3 Physical and Chemical Properties
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Question 2Salt completely dissolved in water is best classified as a:
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Answer: D — Homogeneous mixture.
Salt water is a solution: its composition is uniform throughout, but the salt and water are not chemically combined and the proportions can vary. That makes it a homogeneous mixture, not a compound.
Checked against: OpenStax Chemistry 2e, 1.2 Phases and Classification of Matter
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Question 3What determines the identity of an element?
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Answer: A — The number of protons in the nucleus.
Every atom of a given element has the same number of protons, which is its atomic number. Atoms of one element can have different numbers of neutrons (isotopes) or electrons (ions).
Checked against: OpenStax Chemistry 2e, 2.3 Atomic Structure and Symbolism
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Question 4Elements in the same group (vertical column) of the periodic table have similar chemical properties because they have the same:
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Answer: B — Number of valence electrons.
Chemical behavior depends mostly on the outermost (valence) electrons, and elements in a group share the same valence electron arrangement. Elements in the same period (row) share the number of occupied shells, not their properties.
Checked against: OpenStax Chemistry 2e, 2.5 The Periodic Table
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Question 5What type of bond forms between sodium and chlorine in sodium chloride (NaCl)?
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Answer: C — Ionic bond.
Sodium, a metal, transfers an electron to chlorine, a nonmetal, forming Na+ and Cl- ions held together by electrostatic attraction. Covalent bonds share electrons, usually between nonmetals.
Checked against: OpenStax Chemistry 2e, 7.1 Ionic Bonding
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Question 6Which type of reaction is Zn + 2HCl -> ZnCl2 + H2?
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Answer: D — Single replacement.
An element (zinc) replaces another element (hydrogen) in a compound, so this is a single replacement (single displacement) reaction; it is also a redox reaction. In a double replacement, two compounds exchange ions.
Checked against: OpenStax Chemistry 2e, 4.2 Classifying Chemical Reactions
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Question 7Using a molar mass of 18 g/mol for water, how many moles are in 54 g of water?
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Answer: A — 3 mol.
Moles = mass / molar mass = 54 g / 18 g/mol = 3 mol.
Checked against: OpenStax Chemistry 2e, 3.1 Formula Mass and the Mole Concept
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Question 8What is the molarity of a solution made by dissolving 0.50 mol of glucose in enough water to make 250 mL of solution?
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Answer: B — 2.0 M.
Molarity = moles of solute / liters of solution. 250 mL = 0.250 L, so 0.50 mol / 0.250 L = 2.0 M.
Checked against: OpenStax Chemistry 2e, 3.3 Molarity
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Question 9A solution has a pH of 3. It is:
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Answer: D — Acidic.
At 25 °C, pH 7 is neutral, a pH below 7 is acidic and a pH above 7 is basic. A pH of 3 means the hydronium ion concentration is higher than the hydroxide concentration.
Checked against: OpenStax Chemistry 2e, 14.2 pH and pOH
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Question 10A sample contains 80 g of a radioactive isotope with a half-life of 5 days. How much of the isotope remains after 15 days?
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Answer: C — 10 g.
15 days is 3 half-lives. The amount halves each time: 80 g to 40 g to 20 g to 10 g.
Checked against: OpenStax Chemistry 2e, 21.3 Radioactive Decay
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