SAJC_2025 Dec Holiday Assignment_Students

1 St Andrew’s Junior College JC1 H2 Chemistry 2025 Dec Holidays Assignment Name : …………………………………………………… Date : …………………….. Class : 25S……… Time : 1 hour Instructions: • Complete under timed exam conditions (2 min per MCQ, 1.6 min per mark for structured) • Self-mark MCQ, Structured Q1 and Q2. Answers on google drive. • Submit the assignment to your tutor during the first tutorial in 2026. Section A – Multiple Choice Questions [10 marks] For each question, there are four possible answers. Choose the one you consider correct and write your answer in the boxes below. Question 1 2 3 4 5 Answer Question 6 7 8 9 10 Answer 1 10 cm3 of a gaseous hydrocarbon, CxHy, was exploded with an excess of oxygen. There was a contraction of 30 cm3. When the resulting gaseous mixture was treated with aqueous sodium hydroxide, there was a further contraction of 40 cm3. Given that all gas volumes were measured at r.t.p., what is the molecular formula of the hydrocarbon? A C3H8 B C3H10 C C4H8 D C4H10 35

2 2 What is the proton number of an element that has four unpaired electrons in its ground state? A 16 B 22 C 24 D 26 3 The boiling points of pent–1–ene and 2,2–dimethylpropane are 30 C and 9 C respectively. Which statements help to account for this difference in boiling points? 1 The molecule of pent–1–ene is less compact than that of 2,2–dimethylpropane. 2 The covalent bonds in pent–1–ene are stronger than those in 2,2–dimethylpropane. 3 Pent–1–ene is a polar molecule while 2,2–dimethylpropane is a non–polar molecule. 4 The intermolecular forces of attraction in pent–1–ene are more extensive than those in 2,2–dimethylpropane. A 1, 2 and 4 only B 2 and 3 only C 1 and 4 only D 3 and 4 only 4 A 5.0 dm3 sample of neon gas at a pressure of 200 kPa and a 2.0 dm 3 sample of helium gas at a pressure of 500 kPa are introduced into a 2.5 dm3 vessel at constant temperature. What is the total pressure in the vessel? A 500 kPa B 700 kPa C 800 kPa D 1000 kPa

3 5 The oxides and chlorides of Mg, Al, Si and P are added separately to excess water. Which of the following shows the correct trends of the pH of the resultant solutions? A B pH of its oxide in water pH of its chloride in water .P .Si .Al .Mg pH of its oxide in water pH of its chloride in water .P .Si .Al .Mg C D pH of its oxide in water pH of its chloride in water .P .Si .Al .Mg pH of its oxide in water pH of its chloride in water .P .Si .Al .Mg 6 Which of the following enthalpy changes is exothermic? A Mg2+(g) + 2Cl–(g) → MgCl2(aq) B Al2O3(s) → 2Al3+(g) + 3O2–(g) C O–(g) + e– → O2–(g) D Br2(g) → 2Br•(g)

4 7 The reaction between NO and Br2 is proposed to proceed via the following mechanism: Step 1: NO + Br2 ⇌ NOBr2 (fast) Step 2: NOBr2 + NO → 2NOBr (slow) Which statements are correct? 1 NOBr2 is a transition sta