A LEVEL CHEMISTRY OCR
PRACTICE EXAM
Question 1: Which atom has the electron con�guration [Ar] 3d⁵ 4s¹?
Choices:
1) V 2) Cr 3) Mn 4) Fe
Correct Answer: Cr
Explanation: Chromium is an exception to the Aufbau principle; it �lls the 4s and 3d subshells with one electron each to achieve a more stable half-�lled 3d subshell.Page 1
Question 2: What is the pH of a 0.050 mol dm⁻³ aqueous solution of barium
hydroxide, Ba(OH)₂, at 298 K? (Kw = 1.0 x 10⁻¹⁴)
Choices:
1) 12.70
2) 13.00
3) 1.00
4) 13.30
Correct Answer: 13.00
Explanation: Ba(OH)₂ fully dissociates to release 2 OH⁻ ions per molecule. [OH⁻] = 0.050 * 2 = 0.100 mol dm⁻³. pOH = -log(0.1) = 1. pH = 14 - 1 = 13.00.Question 3: The standard electrode potentials for two half-cells are: Ag⁺ + e⁻ ⇌ Ag (E° = +0.80 V) and Cu²⁺ + 2e⁻ ⇌ Cu (E° = +0.34 V). What is the standard cell potential?
Choices:
1) +1.14 V
2) +0.46 V
3) +1.26 V
4) -0.46 V
Correct Answer: +0.46 V
Explanation: The standard cell potential is the di�erence between the more positive and less
positive potentials: +0.80 V - (+0.34 V) = +0.46 V.
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Question 4: Which compound exhibits geometric (E/Z) isomerism?
Choices:
1) But-1-ene 2) 2-methylbut-2-ene 3) 1,2-dichloroethene 4) Propene
Correct Answer: 1,2-dichloroethene
Explanation: Geometric (E/Z) isomerism requires restricted rotation around a C=C bond and two di�erent groups attached to each carbon of the double bond. 1,2-dichloroethene meets both criteria.Question 5: What is the systematic IUPAC name for the molecule with the structural formula CH₃CH(OH)CH₂CHO?
Choices:
1) 3-hydroxybutanal 2) 2-hydroxybutanal 3) 4-hydroxybutan-2-one 4) 3-hydroxybutan-1-one
Correct Answer: 3-hydroxybutanal
Explanation: The aldehyde group gets priority and is on carbon 1. The hydroxyl group is on carbon 3 of the four-carbon chain, making it 3-hydroxybutanal.Page 3