l"},{"color":"orange","style":"text-color","anchor":"used"},{"color":"amber","style":"text-color","anchor":"left"},{"color":"green","style":"text-color","anchor":"chlorine"}]},"order":3,"title":"Finish hydrogen and chlorine","description":"Seven water molecules need 14 hydrogen atoms, so place 14 before hydrochloric acid. Fourteen HCl provide 14 chlorine atoms. The 2 KCl and 2 CrCl3 use 8 chlorine atoms, leaving 6 chlorine atoms, so use 3 Cl2. This fully balanced equation earns A1."}]}],"generatedAt":"2026-07-21T04:23:29.943Z","modelVersion":"gpt-5.6-terra","explanationVersion":"v3"},"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"042ce2bc-cb28-4940-94f6-d8b5520a966f","revisionId":"685a0589-f1ce-42e1-86ff-c9ae26021c4b","questionNumber":null,"questionType":"LA","specification":"In deep sedimentary basins, the iron-bearing mineral siderite ($\\text{FeCO}_3$) undergoes diagenetic alteration in the presence of pore-water calcium ions to form the double carbonate mineral ankerite, $\\text{CaFe}(\\text{CO}_3)_2$.","difficulty":5,"difficultyBand":"medium","totalMarks":2,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"2222407a-af67-48d1-ae5b-0bca6a5e4800","label":null,"content":"Complete the ionic equation for this conversion of siderite into ankerite.\n\n$$\\text{.....}\\text{FeCO}_3 + \\text{.....} \\rightarrow \\text{CaFe}(\\text{CO}_3)_2 + \\text{Fe}^{2+}$$","markscheme":"- Identifies the missing reactant ion as $\\text{Ca}^{2+}$ B1\n- Correctly balances the equation with a coefficient of $2$ in front of $\\text{FeCO}_3$ to give:\n $$2\\text{FeCO}_3 + \\text{Ca}^{2+} \\rightarrow \\text{CaFe}(\\text{CO}_3)_2 + \\text{Fe}^{2+}$$ B1","marks":2,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"28222be4-43bf-4be5-85bd-2ac069e18d1c","revisionId":"a3581322-098e-41b7-9c0c-99b06e3bd2a7","questionNumber":null,"questionType":"LA","specification":"Aluminium reacts with oxygen to form aluminium oxide, which provides a protective layer against corrosion.","difficulty":5,"difficultyBand":"medium","totalMarks":3,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"c5fe8ece-2618-4890-bd4a-3074d960b2af","label":null,"content":"Write the balanced chemical equation for the reaction between aluminium and oxygen.","markscheme":"- Identifies the correct formulae for the reactants as $\\text{Al}$ and $\\text{O}_2$ B1\n- Identifies the correct formula for the product as $\\text{Al}_2\\text{O}_3$ B1\n- Correctly balances the overall equation: $4\\text{Al} + 3\\text{O}_2 \\rightarrow 2\\text{Al}_2\\text{O}_3$ B1","marks":3,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null}],"subjectCode":"gcse_chemistry","summaries":[{"id":"007aaa90-372a-4d8f-b1fd-7a681e861b11","difficultyBand":"medium","calculatorUse":null},{"id":"00a3809f-0317-42a2-8c7c-f2d606e038fe","difficultyBand":"easy","calculatorUse":null},{"id":"042ce2bc-cb28-4940-94f6-d8b5520a966f","difficultyBand":"medium","calculatorUse":null},{"id":"04616772-92d2-4180-be0d-277fd5e943bb","difficultyBand":"easy","calculatorUse":null},{"id":"04e29602-7f2c-4d9d-9b1d-e458c44f934a","difficultyBand":"easy","calculatorUse":null},{"id":"055deacb-f3c8-481d-9355-5ee1035bb0c4","difficultyBand":"easy","calculatorUse":null},{"id":"05f52d47-c2d0-4a16-84f5-9e855450e25e","difficultyBand":"easy","calculatorUse":null},{"id":"064834dc-55b3-4cc9-94ef-05dfb5eba2c5","difficultyBand":"easy","calculatorUse":null},{"id":"06836bbf-a9f1-4310-8b0a-4bf8b010164e","difficultyBand":"easy","calculatorUse":null},{"id":"07848642-ab76-4c49-84e7-c1e0f143c4b2","difficultyBand":"easy","calculatorUse":null},{"id":"0805f2fd-cacd-4dab-8b4f-b13e3328557f","difficultyBand":"easy","calculatorUse":null},{"id":"085b6fa6-8382-4c8f-8f19-6ee30dfb9ade","difficultyBand":"easy","calculatorUse":null},{"id":"08edb677-83ac-4cb9-be50-3c4991712232","difficultyBand":"easy","calculatorUs

Formulae, equations and hazards

Question 2

Formulae, equations and hazards Questions

Formulae, equations and hazards

Question 2

Formulae, equations and hazards Questions