The OCR GCSE Chemistry (Gateway Science) Higher Tier Paper 4 from June 2023 examines topics in environmental chemistry, industrial processes, and polymer science. Key areas include bioleaching, electrolysis, chemical cells, and catalytic reactions. Questions assess reaction mechanisms, stoichiometry, dynamic equilibrium, and the greenhouse effect. Practical skills like titration, material analysis, and life-cycle assessments are tested. Sustainability in chemical manufacturing and pollutant impact mitigation feature prominently. The paper emphasizes scientific reasoning, problem-solving, and data interpretation, focusing on optimizing industrial processes and understanding environmental impacts.