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Mistake Review

Mistake Review – Focus on Weak Point

  • Do NOT rush
  • Say reasoning out loud
  • Goal: never miss these again

PART 1: Equilibrium (#1 Weak Area)

Question 1

If Q < K, the reaction will:

  1. shift left
  2. shift right
  3. stop
  4. no change
Show answer

Correct answer: B

Why: Q < K means not enough products → reaction moves forward.

Common mistake: Confusing Q < K with Q > K.

Fix it: Q < K → RIGHT; Q > K → LEFT

Question 2

If Q > K, the reaction will:

  1. shift right
  2. shift left
  3. stop
  4. no change
Show answer

Correct answer: B

Why: Too many products → system shifts left.

Fix it: Too much product → go backward

Question 3

For:
N₂ + 3H₂ ⇌ 2NH₃

If pressure increases:

  1. shift left
  2. shift right
  3. no change
  4. depends
Show answer

Correct answer: B

Why: Left = 4 moles gas
Right = 2 moles gas
→ shift to fewer moles

Fix it: High pressure → fewer gas molecules

Question 4

Removing product causes equilibrium to:

  1. shift left
  2. shift right
  3. no change
  4. stop
Show answer

Correct answer: B

Why: System tries to replace removed product.

Fix it: Remove product → make more product

Question 5

For an exothermic reaction, increasing temperature:

  1. shifts right
  2. shifts left
  3. no change
  4. increases K
Show answer

Correct answer: B

Why: Heat is product → adding heat shifts left.

Fix it: Exo + heat → LEFT
Endo + heat → RIGHT

Question 6

Which factor changes K?

  1. pressure
  2. concentration
  3. catalyst
  4. temperature
Show answer

Correct answer: D

Why: Only temperature changes equilibrium constant.

Fix it: Only TEMP affects K

PART 2: Acid–Base Precision (#2)

Question 7

What is pH of 1×10⁻⁵ M HCl?

  1. 3
  2. 4
  3. 5
  4. 6
Show answer

Correct answer: C

Why: pH = -log(10⁻⁵) = 5

Fix it: Exponent = pH

Question 8

Which has highest pH?

  1. 1 M acid
  2. 0.1 M acid
  3. 0.01 M acid
  4. 0.001 M acid
Show answer

Correct answer: D

Why: More dilute → fewer H⁺ → higher pH

Fix it: Dilution ↑ → pH ↑

Question 9

Adding acid to a buffer will:

  1. big decrease
  2. small decrease
  3. increase pH
  4. no change
Show answer

Correct answer: B

Why: Buffer resists change.

Common mistake: Thinking big pH change.

Fix it: Buffer = small change only

Question 10

Diluting an acid:

  1. lowers pH
  2. raises pH
  3. no change
  4. neutralizes
Show answer

Correct answer: B

Why: [H⁺] decreases → pH increases

Fix it: Dilution = less acidic

FINAL 10 QUESTIONS (AP 5-Level Training)

Question 11 (Q vs K Trap)

For a reaction, Q = 0.5 and K = 5. What happens?

  1. shift left
  2. shift right
  3. no change
  4. stop
Show answer

Correct answer: B

Why: Q < K → not enough product → shift right.

Trap: Students reverse Q and K.

Fix it: Q < K → RIGHT; Q > K → LEFT

Question 12 (Exo vs Endo Trap)

For an exothermic reaction, increasing temperature:

  1. increases K
  2. decreases K
  3. no change
  4. shifts right
Show answer

Correct answer: B

Why: Heat is product → adding heat shifts left → less product → K decreases.

Trap: Students think temp always increases K.

Fix it: Exo → temp ↑ → K ↓
Endo → temp ↑ → K ↑

Question 13 (Pressure + Moles)

If pressure increases, equilibrium shifts toward:

  1. more gas moles
  2. fewer gas moles
  3. solids
  4. liquids
Show answer

Correct answer: B

Why: System reduces pressure by lowering gas particles.

Trap: Forgetting to COUNT moles.

Fix it: Pressure ↑ → fewer moles

Question 14 (Catalyst Trap)

Adding a catalyst will:

  1. increase K
  2. shift equilibrium
  3. speed reaction
  4. increase products
Show answer

Correct answer: C

Why: Catalyst lowers activation energy only.

Trap: Thinking equilibrium shifts.

Fix it: Catalyst = faster ONLY

Question 15 (K Expression Trap)

Which is included in K?

  1. solids
  2. liquids
  3. gases
  4. none
Show answer

Correct answer: C

Why: Only (g) and (aq) included.

Trap: Students include everything.

Fix it: Ignore solids & liquids

Question 16 (pH Quick Calculation)

What is pH of 1×10⁻⁶ M HCl?

  1. 4
  2. 5
  3. 6
  4. 7
Show answer

Correct answer: C

Why: pH = -log(10⁻⁶) = 6

Trap: Overthinking log.

Fix it: Exponent = pH

Question 17 (pH vs Strength Trap)

Which is MOST acidic?

  1. 0.1 M HCl
  2. 0.01 M HCl
  3. 0.001 M HCl
  4. 1 M HCl
Show answer

Correct answer: D

Why: Highest concentration → most H⁺ → lowest pH.

Trap: Confusing dilution.

Fix it: More concentrated → more acidic

Question 18 (Buffer Trap)

A buffer resists pH change because:

  1. it is neutral
  2. it reacts with added acid/base
  3. it has high pH
  4. it stops reactions
Show answer

Correct answer: B

Why: Buffer components neutralize added acid/base.

Trap: Thinking buffer = neutral.

Fix it: Buffer = reacts to stabilize

Question 19 (Dilution Trap)

Diluting a base will:

  1. increase pH
  2. decrease pH
  3. no change
  4. neutralize
Show answer

Correct answer: B

Why: [OH⁻] decreases → pH decreases.

Trap: Mixing acid/base logic.

Fix it: Dilute base → less basic

Question 20 (Equilibrium Concept)

At equilibrium:

  1. reaction stops
  2. forward = reverse rate
  3. equal concentrations
  4. no movement
Show answer

Correct answer: B

Why: Dynamic equilibrium → reactions still occur.

Trap: Thinking reaction stops.

Fix it: Rates equal, not amounts

PART 3: FRQ Precision (CRITICAL FOR 5)

FRQ 1

Explain effect of catalyst

Show answer

Perfect Answer:
A catalyst lowers activation energy, increasing the rate of both forward and reverse reactions equally. It does not change the equilibrium constant or equilibrium position.

FRQ 2

Explain equilibrium shift with temperature (endothermic)

Show answer

Perfect Answer:
In an endothermic reaction, heat acts as a reactant. Increasing temperature adds heat, shifting equilibrium to the right to produce more products.

FRQ 3

Explain dilution effect

Show answer

Perfect Answer:
Dilution decreases the concentration of H⁺ ions, which increases the pH of the solution.