BBSS Prelim P2 Ans

1 Bukit Batok Secondary School Sec 4 Express Chemistry (6092) Prelim Exam 2024 Answers 1a The molecules lose energy to the surroundings and slow down in their movement hence coming closer together making the air more dense / denser. (More collisions between air molecules on the bottom of aeroplane caused more lift) 1m 1m 1bi Flooding of low-lying areas leading to loss of crops/destruction of animal habitats. 1m 1bii Increase in usage of carbon containing fuels Higher usage or presence of cars Deforestation either 1m 1biii CS is expensive as it takes a lot of equipment to capture, purify, liquefy, transport and bury CO2. Safety concerns because it is uncertain what the consequences will be if there is leakage of large amounts of CO2. One might imagine that large amounts of CO2 could escape and incapacitating humans and animals. CO2 is a gas that occurs in nature, but can be dangerous in large, concentrated quantities. accept answers relevant to context of question either 1m 2a Titanium, carbon, magnesium 1m 2b The magnesium chloride produced in reactor 2 is collected and electrolysed to produce magnesium metal which is then used to react with titanium chloride again. Chlorine produced by electrolysis is used to react with rutile to produce titanium chloride in reactor 1. either 1m 2c Argon is used to provide an unreactive/ inert atmosphere to prevent the oxidation of / reaction of oxygen with magnesium / titanium / titanium chloride. 1m 2d Wash the mixture with water to dissolve the soluble magnesium chloride. 1m Filter the mixture to obtain titanium as the residue. 1m

2 3a true false An iron catalyst is used. √ The reaction is reversible and so the conditions must be chosen carefully to give the best yield. √ A good yield of ammonia is obtainable even without the use of high pressure. √ Nitrogen from the air is converted into a substance from which nitrogenous fertilisers can be easily produced. √ 4√ - 2m 2-3√ - 1m 1√ - 0m 3b (i) sodium hydroxide is added to A and warm 1m (ii) (dilute) nitric acid and barium nitrate is added to A 1m (iii) blue precipitate formed is insoluble in excess sodium hydroxide 1m (iv) sodium hydroxide and aluminium foil are added to A and warm 1m (v) ammonium iodide 1m 4a R f value of yellow dye is 0 in pure water. Thus yellow dye does not dissolve in pure water and be separated. 1m R f value of red dye is 0 in pure ethanol. Thus red dye is insoluble in pure ethanol and unable to be separated. 1m 4b All 3 dyes have same Rf value of 0.4 when solvent has 80% ethanol. 1m 4c Total volume = 80 + 120 = 200 cm3 1m %ethanol = (80/200) x 100 = 40% R f value of blue dye 0.6 Rf value of red dye 0.6 Rf value of yellow dye 0.04 1m 4d No. When solvent has 40% ethanol, blue and red dyes have the same Rf value thus will not be separated. 1m 5ai CH 3COOH + NaOH