AP Chem Unit 4

2 H₂O₂(l) → 2 H₂O(l) + O₂(g)

The exothermic process represented above is best classified as a

• physical change because a new phase appears in the products

• physical change because O₂(g) that was dissolved comes out of solution

• chemical change because entropy increases as the process proceeds

• chemical change because covalent bonds are broken and new covalent bonds are formed

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TRA-1.A

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

A student had two dilute, colorless solutions, HCl(aq) and NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?

• The resulting solution is colorless.

• The temperature of the reaction mixture increases.

• The total volume of the mixture is approximately equal to the sum of the initial volumes.

• The resulting solution conducts electricity.

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TRA-1.A

A student was asked to formulate a hypothesis about what would happen if 100.mL of 0.1M NaOH(aq) at 25°C was combined with 100. mL of 0.1M MgCl₂(aq) at 25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?

• The volume of the resulting solution will be equal to the sum of the volumes of the original solutions.

• The mass of the resulting solution will be equal to the sum of the masses of the original solutions.

• The resulting solution would contain a precipitate.

• The resulting solution will be clear.

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TRA-1.A

A student was studying physical and chemical changes. The student carried out some procedures in the laboratory and recorded observations. For one of the procedures, the student concluded that a physical change took place, but not a chemical change. Which of the following could have been the results of the procedure?

• A cube of metal was changed into a flat sheet of metal.

• When two liquids at room temperature were combined in a beaker, the beaker became hot.

• When two clear liquids were combined, the resulting mixture was cloudy.

• When a colorless liquid was added to a blue liquid, the resulting solution was yellow.

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TRA-1.A

Which of the following is the balanced net-ionic equation for the reaction between Li(s) and water?

• 2 Li(s) + 2 H⁺(aq) + 2 OH⁻(aq) → 2 Li⁺(aq) + 2 OH⁻(aq) + H₂(g)

• 2 Li(s) + 2 H₂O(l) → 2 Li⁺(aq) + 2 OH⁻(aq) + H₂(g)

• 2 Li(s) + 2 H₂O(l) → 2 LiOH(s) + H₂(g)

• 2 Li(s) + 2 H₂O(l) → 2 LiH(s) + H₂(g)

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TRA-1.B

A 0.50g sample of Mg(s) was placed in a solution of HCl(aq), where it reacted completely.

Which of the following equations best represents the reacting species in the reaction described above?

• Mg(s) + 2 H⁺(aq) → Mg²⁺(aq) + H₂(g)

• Mg(s) + HCl(aq) → MgCl₂(aq) + H₂(g)

• Mg(s) + 2 HCl(aq) → MgCl₂(s) + 2 H⁺(aq)

• Mg(s) + 2 HCl(aq) → Mg²⁺(aq) + Cl₂(g) + H₂(g)

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TRA-1.B

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?

• NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq)

• Na⁺(aq) + F^-(aq) + H⁺(aq) + Cl^-(aq) → Na⁺(aq) + Cl^-(aq) + HF(aq)

• Na⁺(aq) + Cl^-(aq) → NaCl(aq)

• F^-(aq) + H⁺(aq) → HF(aq)

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TRA-1.B

Equal volumes of 0.2⁢M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?

• Pb²⁺(aq) + Br^-(aq) → PbBr₂(s)

• K⁺(aq) + NO₃^-(aq) → KNO₃(aq)

• Pb²⁺(aq) + 2 NO₃^-(aq) + 2 K⁺(aq) + 2 Br^-(aq) → 2 NO₃^-(aq) + 2 K⁺(aq) + PbBr₂(s)

• Pb(NO₃)₂(aq) + 2 KBr(aq) → PbBr₂(s) + 2 KNO₃(aq)

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TRA-1.B

The reaction between aqueous strontium chloride (SrCl₂) and aqueous potassium sulfate (K₂SO₄) forms a precipitate of strontium sulfate (SrSO₄). Which of the following represents the net ionic equation for the reaction?

• Sr²⁺(aq) + SO₄^-(aq) → SrSO₄(s)

• K⁺(aq) + Cl^-(aq) → KCl(aq)

• Sr²⁺(aq) + 2 Cl^-(aq) + 2 K⁺(aq) + SO₄^-(aq) → 2 Cl^-(aq) + 2 K⁺(aq) + SrSO₄(s)

• SrCl₂(aq) + K₂SO₄(aq) → SrSO₄(s) + 2 KCl(aq)

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TRA-1.B

A 20. mL sample of 0.50 M HC₂H₃O₂(aq) is titrated with 0.50 M NaOH(aq). Which of the following best represents the species that react and the species produced in the reaction?

• H⁺(aq) + OH⁻(aq) → H₂O(l)

• H⁺(aq) + C₂H₃O₂⁻(aq) + Na⁺(aq) + OH⁻(aq) → H₂O(l) + NaC₂H₃O₂(aq)

• HC₂H₃O₂(aq) + OH^-(aq) → C₂H₃O₂^-(aq) + H₂O(l)

• HC₂H₃O₂(aq) + NaOH(aq) → H₂O(I) + Na⁺(aq) + C₂H₃O₂^-(aq)