IB DP Chemistry Mock Exam HL Paper 2 Set 1 - 2025 Syllabus
IB DP Chemistry Mock Exam HL Paper 2 Set 1
Prepare for the IB DP Chemistry Exam with our comprehensive IB DP Chemistry Exam Mock Exam HL Paper 2 Set 1. Test your knowledge and understanding of key concepts with challenging questions covering all essential topics. Identify areas for improvement and boost your confidence for the real exam
Question
[Co(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌ [CoCl₄]²⁻(aq) + 6H₂O(l)
Pink Blue
▶️ Answer/Explanation
(a)
The cobalt atom (Co, Z=27) has the electron configuration [Ar] 4s² 3d⁷. The Co²⁺ ion loses two electrons from the 4s orbital first, resulting in the configuration [Ar] 3d⁷.
\(\boxed{[Ar] 3d^7}\) or \(\boxed{1s^2 2s^2 2p^6 3s^2 3p^6 3d^7}\)
(b)(i)
Adding solid NaCl increases the concentration of Cl⁻(aq) ions. According to Le Chatelier’s principle, the equilibrium will shift to the right to reduce this disturbance, favouring the formation of the blue [CoCl₄]²⁻ complex. The equilibrium constant, K, is unaffected by changes in concentration at constant temperature.
\(\boxed{\text{K is unchanged, equilibrium shifts to the right.}}\)
(b)(ii)
Heating the mixture causes a colour change from pink to blue, indicating an increase in the concentration of the product, [CoCl₄]²⁻. According to Le Chatelier’s principle, if increasing temperature favours the forward reaction, the reaction must be endothermic.
\(\boxed{\text{Endothermic, because heating favours the forward reaction.}}\)