CART - Chemistry Acceleration Readiness Chemical Reactions and Equations Questions and Answers — Questions and Answers
Question 1: When the equation for the complete combustion of propane (C₃H₈) is balanced using the smallest whole-number coefficients, what is the coefficient for oxygen (O₂)? _ C₃H₈ + _ O₂ → _ CO₂ + _ H₂O
- 3
- 7
- 5 (Correct answer)
- 10
Correct answer: 5
To balance the equation, first balance Carbon (3 on left, so 3 CO₂ on right). Then balance Hydrogen (8 on left, so 4 H₂O on right). Finally, balance Oxygen. The right side now has (3*2) + (4*1) = 10 oxygen atoms. To get 10 oxygen atoms on the left, the coefficient for O₂ must be 5. The balanced equation is C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
Question 2: The reaction between aqueous silver nitrate and aqueous sodium chloride produces solid silver chloride and aqueous sodium nitrate. How is this reaction best classified? AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
- Synthesis
- Double Displacement (Precipitation) (Correct answer)
- Single Displacement
- Decomposition
Correct answer: Double Displacement (Precipitation)
This reaction is a double displacement (or metathesis) reaction because the cations (Ag⁺ and Na⁺) and anions (NO₃⁻ and Cl⁻) from the two reactant compounds exchange partners to form two new compounds. Since one of the products, AgCl, is an insoluble solid (a precipitate), it is also specifically classified as a precipitation reaction.
Question 3: Aqueous solutions of lead(II) nitrate, Pb(NO₃)₂, and potassium iodide, KI, are mixed, resulting in the formation of a solid precipitate. What is the correct net ionic equation for this reaction?
- K⁺(aq) + NO₃⁻(aq) → KNO₃(s)
- Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)
- Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s) (Correct answer)
- Pb²⁺(aq) + 2NO₃⁻(aq) + 2K⁺(aq) + 2I⁻(aq) → PbI₂(s) + 2KNO₃(s)
Correct answer: Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s)
The balanced molecular equation is Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq). The spectator ions, which do not participate in the formation of the precipitate, are K⁺(aq) and NO₃⁻(aq). Removing these from the complete ionic equation leaves the net ionic equation, which shows only the species that react to form the solid lead(II) iodide.
Question 4: In the following redox reaction, which substance is oxidized? 2Fe(s) + 3Cl₂(g) → 2FeCl₃(s)
- Fe (Correct answer)
- Cl₂
- FeCl₃
- This is not a redox reaction.
Correct answer: Fe
Oxidation is the loss of electrons, characterized by an increase in oxidation number. Elemental iron (Fe) starts with an oxidation state of 0. In the product, iron(III) chloride (FeCl₃), iron has an oxidation state of +3. Since the oxidation number of iron increases, it is the substance that is oxidized.
Question 5: A chemist completely reacts 13.08 g of zinc metal (Zn) with an excess of hydrochloric acid (HCl) according to the balanced equation: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g). What volume of hydrogen gas (H₂) is produced at Standard Temperature and Pressure (STP)? (Molar mass of Zn = 65.38 g/mol)
- 2.24 L
- 1.12 L
- 8.96 L
- 4.48 L (Correct answer)
Correct answer: 4.48 L
First, convert the mass of zinc to moles: 13.08 g Zn / 65.38 g/mol = 0.200 mol Zn. The mole ratio between Zn and H₂ is 1:1, so 0.200 mol of H₂ is produced. At STP (0°C and 1 atm), one mole of any ideal gas occupies 22.4 L. Therefore, the volume is 0.200 mol H₂ × 22.4 L/mol = 4.48 L.
Question 6: Which of the following single displacement reactions will occur spontaneously according to the metal activity series?
- Cu(s) + AlCl₃(aq) →
- Ag(s) + HCl(aq) →
- Zn(s) + CuSO₄(aq) → (Correct answer)
- Fe(s) + MgCl₂(aq) →
Correct answer: Zn(s) + CuSO₄(aq) →
A single displacement reaction occurs when a more reactive element displaces a less reactive element from a compound. According to the activity series, zinc (Zn) is more reactive than copper (Cu), so it will displace copper from copper(II) sulfate. In the other options, the elemental metals (Cu, Ag, Fe) are less reactive than the metal ions they would need to displace (Al³⁺, H⁺, Mg²⁺), so no reaction will occur.
CART - Chemistry Acceleration Readiness Chemical Reactions and Equations Questions and Answers
When the equation for the complete combustion of propane (C₃H₈) is balanced using the smallest whole-number coefficients, what is the coefficient for oxygen (O₂)?
_ C₃H₈ + _ O₂ → _ CO₂ + _ H₂O