Скачать или смотреть MCAT General Chemistry Practice Question-04: Type of Reactions-Double Displacement Reaction-Subtype

MCAT General Chemistry Practice Question-04: Type of Reactions-Double Displacement Reaction-Subtype

Double Displacement Reactions for MCAT | Precipitation, Neutralization, Gas Evolution


Struggling with double displacement reactions for the MCAT? In this video, we break down the key types — precipitation, acid-base neutralization, and gas-forming reactions — using real MCAT-style practice questions.

🧪 What you'll learn:
Introduction
General Formula: AB + CD → AD + CB
Precipitation Reaction Example
Acid-Base Reaction Breakdown
Gas Evolution Reactions on the MCAT
Practice Tips

📘
🔔 Subscribe for more MCAT chemistry practice: [channel link]

#MCATPrep #DoubleDisplacement #MCATChemistry #PreMed #OrganicChemistry #PracticeQuestions





General Form of a Double Displacement Reaction

AB + CD → AD + CB

A and C = cations (positive ions)

B and D = anions (negative ions)

The cations swap anions, forming two new compounds.

Occurs typically in aqueous solutions


Three common subtypes:

1. Precipitation reactions – form an insoluble solid


2. Neutralization reactions – acid + base → salt + water


3. Gas-forming reactions – form a gas + water




---

🧪 Question 1: Precipitation

Which of the following reactions follows the general double displacement form and results in a precipitate?

A. H₂ + O₂ → H₂O
B. Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
C. Ca + 2HCl → CaCl₂ + H₂
D. CH₄ + O₂ → CO₂ + H₂O

General Form Used:
AB (Na₂SO₄) + CD (BaCl₂) → AD (BaSO₄) + CB (NaCl)

Answer: B

Explanation:
This is a double displacement reaction. Na⁺ and Ba²⁺ switch partners. BaSO₄ is insoluble in water, so it precipitates out. The other ions remain in solution.

👉 Type: Double displacement – precipitation


---

🧪 Question 2: Acid–Base Neutralization

Which of the following best demonstrates a double displacement reaction of the acid–base type?

A. NaOH + HNO₃ → NaNO₃ + H₂O
B. Zn + CuSO₄ → ZnSO₄ + Cu
C. NH₄NO₃ → N₂O + 2H₂O
D. CH₄ + 2O₂ → CO₂ + 2H₂O

General Form Used:
AB (NaOH) + CD (HNO₃) → AD (NaNO₃) + CB (H₂O)

Answer: A

Explanation:
This is a neutralization reaction, a subtype of double displacement. Na⁺ from the base and NO₃⁻ from the acid form salt (NaNO₃), and H⁺ + OH⁻ → H₂O.

👉 Type: Double displacement – acid–base neutralization


---

🧪 Question 3: Gas Evolution

Which reaction represents a double displacement that produces a gas?

A. Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O
B. Mg + HCl → MgCl₂ + H₂
C. H₂O₂ → H₂O + O₂
D. CaCO₃ → CaO + CO₂

General Form Used:
AB (Na₂CO₃) + CD (HCl) → AD (NaCl) + CB (H₂CO₃)
(H₂CO₃ then decomposes to CO₂ + H₂O)

Answer: A

Explanation:
Initial double displacement forms carbonic acid (H₂CO₃), which immediately breaks down into CO₂ gas and water. This makes it a gas-forming double displacement reaction.

👉 Type: Double displacement – gas evolution


---

🧪 Question 4: Identifying the Reaction Type

Which of the following is NOT a double displacement reaction?

A. K₂CO₃ + CaCl₂ → CaCO₃ + 2KCl
B. Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃
C. HCl + NaOH → NaCl + H₂O
D. 2H₂ + O₂ → 2H₂O

Answer: D

Explanation:
Choice D is a synthesis reaction, not a double displacement. The others follow the AB + CD → AD + CB format.

👉 Type: Not double displacement — synthesis


---

🧪 Question 5: Predicting Products

What are the products of the double displacement reaction between Al(NO₃)₃ and Na₂CO₃ in aqueous solution?

A. Al₂(CO₃)₃ + NaNO₃
B. AlCO₃ + NaNO₃
C. AlNO₃ + NaCO₃
D. No reaction

General Form Used:
AB (Al(NO₃)₃) + CD (Na₂CO₃) → AD (Al₂(CO₃)₃) + CB (NaNO₃)

Answer: A

Explanation:
Al³⁺ and CO₃²⁻ form Al₂(CO₃)₃, which is insoluble and precipitates. Na⁺ and NO₃⁻ form soluble NaNO₃.

👉 Type: Double displacement – precipitation