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ABSTRACT This study examines how integrating sustainability through socio‐scientific issue (SSI) in secondary chemistry teaching shapes epistemic openness and closure from a decolonial perspective, as mediated through classroom discourse. Drawing on a co‐planned lesson on copper mining in Chile – a scientifically rich yet ethically and politically charged context – I analyse how pedagogical decisions positioned chemistry either as an apolitical framing (Gandolfi 2025b) or as a practice entangled with extractivism, environmental injustice, and responsibility. Using reflexive thematic analysis of lesson audio recordings, student artefacts, and researcher fieldnotes, and interpreting classroom interaction through Mortimer and Scott's (2003) communicative approaches and Gandolfi's (2025a) decolonial framework, I identify three key pedagogical moments across the lesson. Findings show that dialogic discourse initially opened space for students' ethical concerns but remained limited without follow‐up that foregrounded structural causes of harm. A subsequent authoritative focus consolidated disciplinary understanding while producing epistemic closure. Epistemic openness was later re‐activated when chemical evidence was reconnected to sustainability and enacted materially through waste‐management deliberations. Findings suggest that decolonial perspectives in chemistry education can move teaching beyond content delivery toward pedagogies that centre justice, epistemic plurality, and critical engagement with real‐world challenges, while remaining contingent on communicative shifts and deliberate pedagogical mediation.
Denise Quiroz‐Martínez (Sat,) studied this question.