SAJC_2025 Dec Hol Revision Package (SDL)_Questions

1 Topic 1: The Mole Concept, Stoichiometry and Redox 1. SRJC/PRELIMS 2011/P3/1(a), (b) Acrylamide is a compound that is found in many deep fried foods such as French fries and potato chips. It is believed to be carcinogenic. (a) Acrylamide contains 50.7% by mass of carbon, 7.0% by mass of hydrogen, 19.8% by mass of nitrogen and 22.5% by mass of oxygen. Given that the relative molecular mass of acrylamide is 71.0, (i) determine the molecular formula of acrylamide. (ii) Hence, draw a possible structure of acrylamide. Hint: an amide has the following functional group (b) Acrylamide is also found in beverages such as prune juice and coffee. Studies show that a person can safely ingest up to 0.5 mg / kg body weight in a day without any observed adverse effects. Given that 1 kg of brewed coffee contains 1.2 × 10−7 mol of acrylamide, calculate the maximum volume of coffee a 50 kg woman can drink per day. You may assume that coffee has the same density as water.

2 2. RVHS/PRELIMS 2011/P3/4(b) Chlorine can also be used to synthesize a bromine-containing oxoanion that is mainly used in continuous or batch dyeing processes. When chlorine is passed through an aqueous solution containing potassium hydroxide and potassium bromide, the bromide ions are oxidised to the bromine-containing oxoanion. Careful addition of aqueous lead nitrate to the resulting solution precipitates 4.17 g of PbCl2. When this precipitate is filtered off and the resulting filtrate is evaporated, 0.835 g of a white crystalline solid is obtained. The white solid has the following composition by mass: K, 23.4 %; Br, 47.8 %; O, 28.8 %. (i) Determine the formula of the white crystalline solid. (ii) Calculate molar ratio of white crystalline solid to lead chloride formed. (iii) Hence, construct a balanced equation for the reaction between chlorine, potassium bromide and potassium hydroxide.

3 3. NYJC/PRELIMS 2014/P2/4(b) In an experiment, H 2S was reacted with 12.00 cm 3 of 0.30 mol dm –3 of an unknown bromate ion, BrO x– in acidic medium to form sulfur, S, of mass 0.289 g and bromine solution. Deduce the oxidation state of Br in BrOx–, and hence the value of x. Criteria of Success Checklist For each question, tick if you have  provided clear s____________ for ALL working  presented i____________ answers to 4 s.f.  presented final answers to ________  provided units, when applicable  presented value of Ar or Mr to _________., when applicable Things to note: • Conversion of units for volume: 1 dm3 = _________ cm3 = ________ m3 1 cm3 = _________ dm3 = ________ m3 1 m3 = _________ dm3 = ________ cm3 • In the calculation of empirical formula from experimental data, if the following figures are obtained for the number of moles, they are usually multiplied by a factor in order to get the correct