Unit 4 Question Bank AP CHEM

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At 27°C, five identical rigid 2.0 L vessels are filled with N₂(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO₃(s), NaBr(s), Cu(s), or I₂(s), as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N₂(g) in each vessel is 720 mm Hg. All four vessels are heated to 127°C and allowed to reach a constant pressure.

At 127°C, the pressure in vessel 1 is found to be higher than that in vessel 2. Which of the following reactions best accounts for the observation?

• NaHCO₃(s) → Na(s) + HCO₃(s)

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  NaHCO₃(s) → NaH(s) + CO₃(s)

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  2 NaHCO₃(s) → Na₂CO₃(s) + CO₂(g) + H₂O(g)

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  2 NaHCO₃(s) + N₂(g) → 2 NaNO₃(s) + C₂H₂(g)

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)

  
  

Based on the chemical equations given, which of the following statements is correct?

• HCN is a weaker acid thanH20

• CN^- is a stronger acid thanHCN

• CN^- is a stronger base thanHCN

• CN^- is a weaker base thanHCN

The diagrams above represent solutes present in two different dilute aqueous solutions before they were mixed. Water molecules are not shown. When the solutions were combined, a precipitation reaction took place. Which of the diagrams below is the best particle representation of the mixture after the precipitation reaction occurred?

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When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powdered Fe, a reaction occurs according to the equation above. When the reaction is complete at 273 K and 1.0 atm, which of the following is true?

• HCl is in excess, and 0.100 mol of HCl remains unreacted.

  
  

• HCl is in excess, and 0.020 mol of HCl remains unreacted.

  
  

• 0.015 mol of FeCl₂ has been produced.

  
  

• 0.22 L of H₂ has been produced.

  
  

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu, a student dissolves a small preweighed sample in HNO₃(aq). Ag⁺(aq) and Cu²⁺(aq) ions form in the solution. Which of the following should be the next step in the analytical process?

• Centrifuging the solution to isolate the heavier ions

  
  

• Evaporating the solution to recover the dissolved nitrates

  
  

• Adding enough base solution to bring the pH up to 7.0

  
  

• Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions