The OCR GCSE Chemistry (Gateway Science) Higher Tier Paper 4 from November 2021 assesses advanced topics like bioleaching, fractional distillation, reaction kinetics, and polymerisation. Key areas include the Haber process, corrosion, equilibrium, and life-cycle assessments. Questions involve energy efficiency, atom economy, and sustainable practices. Practical applications feature titration, mass spectrometry, and infrared spectroscopy. The paper emphasizes environmental impacts, industrial processes, and data interpretation, integrating theoretical knowledge with real-world chemical applications and problem-solving. Analytical skills are tested through calculations, experimental design, and optimization of reaction conditions.