YIJC 2025 Prelim P4 MS (for exchange)_H2 Chem

1 © YIJC 9729/04/JC2/PE/2025 YIJC 2025 Prelim Paper 4 Mark Scheme Hierarchy to be used in calculating mean titres in question 1(b)(i): • Value of 2 identical titres • Average of titres within 0.05 cm3 • Average of titres within 0.10 cm3 Use the selected titres to determine the mean titre for the end-point. 1. For calculations, the principle of no double penalty (error carried forward) applies. For connecting parts, marking from point of first penalty onwards will be based on correct method only. 2. Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks should not be awarded if the keywords are used incorrectly. 3. The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for any correct statement that is contradicted within the same question part. Wrong science that is irrelevant to that question should be ignored. 4. Although spellings do not have to be correct, spelling of syllabus terms must allow for clear and unambiguous separation from other syllabus terms with which they may be confused. (e.g., ethane/ethene)

2 © YIJC 9729/04/JC2/PE/2025 Question Answer Marks 1(b)(i) M1 (MMO Quality) SAMPLE DATA Initial burette reading / cm3 4.10 2.20 Burette reading at first end-point / cm3 26.10 24.20 Burette reading at second end-point / cm3 37.20 35.20 Volume of FA 3 used to complete reactions 1 and 2 / cm3 22.00 22.00 Volume of FA 3 used to complete reaction 3 / cm3 11.10 11.00 Total volume of FA 3 used for titration / cm3 33.10 33.00 Has at least two uncorrected titres for end point within 0.10 cm3 for total volume of FA 3 required for the titration. A student’s “rough”/”trial” titre value can be considered by the examiner when selecting titre values for the mean titre calculation if the student has “validated” this value either by ticking it or by using it in an expression in (b)(ii). (By doing either of these, the student has declared it to be no longer a “rough”/”trial” value) 1 M2 (PDO Record) All the burette readings, for all accurate titres in the titration table, are recorded to the nearest 0.05 cm3. Treat all titres as ‘accurate’ unless labelled ‘rough’ or first titre is recorded to a lower precision than subsequent titres. [For arithmetic errors in calculations in table, deduct M5.] 1 M3, M4 (MMO Quality, MMO Accuracy) Calculate the student’s mean titre (based on total volume of FA 3 required for the titration) as described on page 1. Award M2 and M3 based on the difference, ∆ titre, between Student’s and Supervisor’s mean titre. 2

3 © YIJC 9729/04/JC2/PE/2025 Give 2 marks if this difference is ≤ 0.30cm3 Give 1 marks if this difference is > 0.30cm3 but ≤ 0.50cm3 Give 0 marks for a difference > 0.50cm3 1(b)(ii) M5 (MMO Decision) • (For total volume of FA 3 used for the titration): Student obtains appro