ACJC_H1_CHEM_MCQ_solutions

© ACJC 2017 8872/01/Prelims/17 [Turn over 2 Section A For each question there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1 Ether has the formula, CH3OCH3. In a sample of ether, 8.7 % contains the 18O isotope, with the rest contains the 16O isotope. What is the relative molecular mass of ether in this sample? A 46.2 B 46.8 C 47.2 D 47.8 Ar of O = 8.7 x 18 + 91.3 x 16 /100 = 16.174 Relative Molecular Mass = 16.174 + 12 + 3+ 12 + 3 = 46.174 = 46.2 2 Copper reacts with dilute nitric acid to produce nitrogen dioxide gas. The balanced ionic equation is given. Cu + 2H + + 2HNO3  Cu2+ + 2NO2 + 2H2O Which of the following is correct? Oxidation state of N in Role of copper HNO 3 NO 2 A +5 -3 Reducing agent B +5 +4 Reducing agent C -5 -3 Oxidising agent D -5 +4 Oxidising agent Cu is being oxidised. It is a reducing agent. HNO3 = (+1)+ ? + 3(-2) =0 ? = +5 NO 2 = ？ + 2（-2）= 0 ？= +4

© ACJC 2017 8872/01/Prelims/17 [Turn over 3 3 10 cm 3 of propane was completely burnt in x cm3 of excess oxygen. After cooling to room temperature, the volume of the residual gas was 60 cm 3. The residual gas was passed through aqueous sodium hydroxide was passed through and the volume reduced to y cm3. Which of the following is correct? x y A 50 30 B 60 20 C 70 20 D 80 30 C3H8 + 5O2  3CO2 + 4H2O 10cm 3 requires 50cm3 of oxygen for complete combustion and 30cm3 of CO2 will be produced. Hence x = 50 + (60-30) = 80 cm3. y = volume of excess oxygen = 60-30 cm3 4 An organic compound with the formula C xHyO2 has undergone incomplete combustion, producing carbon dioxide and carbon monoxide in the ratio of 99 : 1. The equation may be represented as follows: CxHyO2 + a O2  b CO + c CO2 + 0.5y H2O a, b and c can be expressed in terms of x and y. Which of the following is correct? a b c A 99x + 0.5x + 0.25y - 1 x 99x B 99x + 0.5x + 0.25y x 99x C 0.99x + 0.005x + 0.25y- 1 0.01x 0.99x D 0.99x + 0.005x + 0.25y 0.01x 0.99x C = 0.01x + 0.99x = x Check by balancing O atoms on both sides, 2 + 2(0.99x + 0.005x + 0.25y- 1) = 0.01x + 0.99x(2) + 0.5y 1.98x+ 0.01x+0.50y = 1.99x + 0.5y

© ACJC 2017 8872/01/Prelims/17 [Turn over 4 5 Use of the Data Booklet is relevant to this question. The components of a 100 g sample of fertilizer is as shown in the table below: Element Mass / g N 15 P 30 K 15 Other Elements 40 The recommended usage of fertilizer is 14 g of fertilizer per 5 dm3 of water. What is the concentration of nitrogen atoms in this recommended solution? A 0.03 mol dm-3 B 0.15 mol dm-3 C 0.42 mol dm-3 D 0.75 mol dm-3 15/100 x 14grams = 2.1 grams No of moles of N = 2.1/14 = 0.15mol Concentration = 0.15/5 = 0.03 mol dm-3 6 The elements X and Y are in Group 16 and 17 respectively in the same period. Which of the following statements regarding X and Y is mo