2021 HCI SAJC TJC H3 Chemistry Answers

RESTRICTED Temasek Junior College Advanced Level Higher 3 Preliminary Examination 9813 Chemistry September 2021 Answer Key 1 HCI SAJC TJC JC2 Preliminary Examination CHEMISTRY Paper 9813/01 Paper 1 This answer key is published as an aid to students, to indicate the requirements of the examination. It shows the basis on which the markers award marks. It does not indicate the details of the discussions that took place before marking began, which would have considered the acceptability of alternative answers. Note: 1. If the candidate’s answer has the same “meaning” or can be clearly inter preted as being of equivalent significance, detail and validity as that in the markscheme then award the mark. Where this point is considered to be particularly relevant in a question it is emphasized by OWTTE (or words to that effect). 2. Occasionally, a part of a question may require an answer that is required for subsequent marking points. If an error is made in the first marking point then it should be penalized. However, if the incorrect answer is used correctly in subsequent marking points then follow through marks should be awarded. When marking, indicate this by adding ECF (error carried forward) on the script. 3. Do not penalize candidates for errors in units or significant figures, unless it is specifically referred to in the answer key. 4. If a question specifically asks for the name of a substance, do not award a mark for a correct formula unless directed otherwise in the answer key. Similarly, if the formula is specifically asked for, unless directed otherwise in the answer key, do not award a mark for a correct name. 5. If a question asks for an equation for a reaction, a balanced symbol equation is usually expected, do not award a mark for a word equation or an unbalanced equation unless directed otherwise in the answer key. 6. Ignore missing or incorrect state symbols in an equation unless directed otherwise in the answer key.

RESTRICTED Temasek Junior College Advanced Level Higher 3 Preliminary Examination 9813 Chemistry September 2021 Answer Key 2 HCI SAJC TJC JC2 Preliminary Examination Question Answer Marks 1(a) Chromium- and selenium-based reagents are toxic; large scale production will generate a lot of wasteful by-products. Getting these by-products removed will add to the cost of production, which is not sustainable. 1 Palladium- and rhodium-based catalyst are expensive and will add to the cost of production. 1 Removing the above -mentioned elements entirely from the product cannot be guaranteed – this is a problem especially when the products are used in medicines. The syntheses thus have no industrial application. (Allow other valid reasons) 1(b) Electronic effect: Use the above and highlight that the radical is resonance stabilised (the lone electron on the 2o carbon is delocalised into the adjacent  system). 1 Hammond postulate: Homolyti