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 simplest ratio. E,g 1.5 (multiply by __ ), 1.33 (multiply by __ ), 1.25 (multiply by __ ), 1.2 (multiply by __ )

4 • In balancing half equations, 1. balance the atom that is not ___ or ____ first. 2. Balance O by adding _____ 3. Balance H by adding ______ 4. Balance charge by adding ____________ Continue with step 5 to 7 for basic medium 5. Add ______ (same number of moles as H+) to both sides of the equation 6. For every mole of H+ + OH- , replace it with 1 mol of _________ 7. Simplify the equation (if necessary) by cancelling out _______ that occurs on both sides of the equation. • For questions to calculate oxidation number in redox reactions, 1. Write out one ______ equation for the known species 2. Work out the _______ ratio of the 2 reactants 3. Using the mole ratio and the half equation written, determine the number of ____________ transferred in the redox reaction. The number of electrons given out by the species that is oxidised will be _____________ by the species that is reduced. 4. Determine the original/final oxidation number by taking into account the final/original oxidation state and the number of electrons taken in/ given out. • For oxidation state, the sign is written ______________ of the number e.g +2, -1.

5 Topic 2: Atomic Structure 1. (a) JJC/PRELIMS 2004/P2/Q1 Particle Electric charge Mass Number Number of Protons Electrons Neutrons X 0 16 16 Y -1 81 36 Z 70 31 28 Complete the table above. (b) (i) Using spdf notation, give the electronic configuration of particle Y and Z. Y: _______________________________ Z: _______________________________ (ii) Compare the ionic size of particle Y and 37Rb+. Give your reason. ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ (c) State, with reasons, whether the first ionization energy of element X is higher or lower when compared with that of (i) phosphorus and (ii) selenium. ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________

6 Things to note: • Criteria of success for electronic configuration include  starting from 1s2 ([Ar] 3d104s24p6 is not acceptable)  superscript to represent number of ___________in the subshell (1s2 or 1s 2 are not acceptable) Note that there should not be commas between subshell (1s 2,2s2,2p6 is unacceptable) • For comparison of ionic radius of isoelectronic ions, answers should compare  nuclear charge ( depends on number of ______________)  ______________ effect (depends on number of inner electrons)  ____________ nuclear charge  conclude that the species with valence electron more strongly __________ would have _______________ionic radius • Criteria of success for decreasing IE trend down the group, state  Se has a larger number of ___________ shells than X, hence ________________ effect increases  The ________________of the valence electrons from the positively charged nucleus is also greater for Se as compared to X  Hence, the valence electrons in Se are less ___________attracted to the nucleus.  ____________energy is needed to remove the ______ (state the subshell) electron in Se compared to 2p (state the subshell) electron in X.  First ionisation energy of Se is lower.

7 2. MJC/PRELIMS 2005/P2/Q1 In an analytical chemistry laboratory, the plasma torch is used to ionize a variety of samples. Samples of unknown elements P – Y (atomic numbers below 20) were passed through the plasma torch and their second ionisation energies were recorded and plotted as shown. (a) Identify the Group in the Periodic Table element W belongs to and write its ground state electronic configuration. Group: __________ Electronic configuration: _______________________________ (b) Element W forms form than one stable chloride. State the formula of one of these chlorides. Draw the dot -and-cross diagram of the chloride of W that you have stated and predict its shape. Shape: ___________________ (c) There are 2 pairs of elements among the elements P – Y that belong to the same group. Identify each pair, stating the respective Groups to which they belong. Pairs Elements Group 1 2

8 ______________________________________________________________ ______________________________________________________________ _________________