Moles in sample=Total Moles200 cm3×75 cm3=0.06675 molMoles in sample equals the fraction with numerator Total Moles and denominator 200 cm cubed end-fraction cross 75 cm cubed equals 0.06675 mol The added H+cap H raised to the positive power ions consume F−cap F raised to the negative power ions via the reaction:
Failing to recognize the stoichiometry of the reaction, particularly the 1:2 ratio between iodine ( I2cap I sub 2 ) and thiosulfate ( S2O32−cap S sub 2 cap O sub 3 raised to the 2 minus power 2. Physical Chemistry: Energetics and Equilibria
A saturated solution of PbI₂ at 25°C was titrated with 0.0200 mol/dm³ AgNO₃. 25.0 cm³ of saturated PbI₂ required 15.5 cm³ of AgNO₃. Calculate Kₛₚ of PbI₂.
The best answers bridged topics, such as using kinetics data to infer reaction mechanisms. A Level H2 Chemistry 2021 Paper 3 Answers
Complex equilibria, buffer calculations, and kinetics.
The structured question section of Paper 3 consists of 5 questions, each carrying a varying number of marks. Here are the answers to the 2021 structured questions:
In this question, students were required to investigate how pH affects the rate of reaction between sodium thiosulfate and hydrochloric acid. Moles in sample=Total Moles200 cm3×75 cm3=0
Consists of 3 to 4 compulsory structured questions, each weighing 15–25 marks.
The highlighted three key patterns:
Comparing the basic strength of phenylamine, ammonia, and ethylamine. Trend: Ethylamine > Ammonia > Phenylamine. Calculate Kₛₚ of PbI₂
ΔG° = ΔH° – TΔS° = (–57.2 × 10³ J mol⁻¹) – (298 K × –175.8 J K⁻¹ mol⁻¹) = –57,200 + 52,388.4 = –4,811.6 J mol⁻¹ ≈ –4.81 kJ mol⁻¹ (2 marks – correct substitution & calculation)
Using the equation Q = mc∆T, where m = 1.00 kg, c = 4.18 J g-1 K-1, and ∆T = 10.0 K, we can calculate Q = 41,800 J. Then, we can calculate ∆H = -41,800 J / 0.100 mol = -418,000 J mol-1 = -418 kJ mol-1.
: Reviews from Reddit described the paper as "shocking" for some, with complaints about a perceived lack of electrochemistry or organic content compared to expectations .