New Curriculum Second Term Chemistry examination for SS 1

Class: SSS 1
Term: Second Term
Subject: Chemistry
Time: 1 hour 30 minutes
Total Marks: 70

SECTION A: OBJECTIVES (40 MARKS)
Instruction: Answer ALL 40 questions. Each carries 1 mark.

1. ________ is the empirical formula of a compound whose molecular formula is C₂H₄. (a) CH₄   (b) CH₂   (c) C₂H₂   (d) C₂H₄
2. All of the following are mixtures except ________. (a) brass   (b) sea water   (c) chemically pure carbon dioxide   (d) air
3. Air in a syringe is readily compressed although the syringe remains sealed. Which particulate explanation is most satisfactory? (a) the absence of any particles in a gas   (b) permanent bonds locking all gas particles in place   (c) gas particles being larger than the syringe   (d) relatively large spaces between gas particles
4. The electron transfer from sodium to chlorine chiefly produces ________. (a) two identical neutral atoms linked only by metallic bonds   (b) oppositely charged ions held by electrostatic attraction   (c) a shared pair of electrons between two chlorine atoms   (d) hydrogen bonds within a sodium atom
5. Which observation is a limitation of the original Dalton model rather than evidence that matter is particulate? (a) Atoms take part in chemical combinations   (b) Matter consists of particles   (c) Atoms of one element can exist as isotopes with different masses   (d) Compounds often form in fixed proportions
6. The ________ is the negatively charged subatomic particle outside the nucleus. (a) Nucleon   (b) Electron   (c) Proton   (d) Neutron
7. Given aluminium valency 3 and oxygen valency 2, the formula of aluminium oxide is ________. (a) Al₃O₂   (b) AlO₂   (c) Al₂O₃   (d) AlO₃
8. An ionised gas glows inside a discharge tube. Which state of matter is represented? (a) plasma   (b) condensate   (c) crystalline solid   (d) aqueous solution
9. Chlorine-35 and chlorine-37 have the same ________ but different ________. (a) proton number; neutron number   (b) mass number; electron charge   (c) neutron number; proton number   (d) total nucleons; atomic number
10. Which action does NOT alter the position of an established equilibrium, although it may speed up attainment? (a) Changing pressure for gas equilibria with different mole counts   (b) Changing temperature   (c) Adding a suitable catalyst   (d) Increasing the concentration of a reactant
11. Why does ordinary filtration fail to recover dissolved sugar from a clear sugar solution? (a) dissolved sugar passes with the solvent through filter paper   (b) sugar molecules always form visible sediment   (c) water immediately turns to steam in every filter   (d) filter paper chemically destroys sugar
12. The direct change from solid iodine to iodine vapour without passing through a liquid is ________. (a) melting   (b) freezing   (c) condensation   (d) sublimation
13. A sealed vessel contains 8 g of reactants before chemical change. What total mass of products should be recovered if nothing escapes? (a) unknown because atoms disappear   (b) 8 g   (c) 4 g   (d) 16 g
14. For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), increased pressure tends to favour ________. (a) neither side because pressure never affects gases   (b) the side with more gas molecules, producing more N₂ and H₂   (c) the side that contains no nitrogen atoms   (d) the side with fewer gas molecules, producing more NH₃
15. Which observation most convincingly distinguishes a compound from a mixture? (a) A compound has a fixed chemical composition; a mixture may vary in composition   (b) A compound always contains visible grains; a mixture is always uniform   (c) Only mixtures can contain more than one element   (d) Mixtures are formed exclusively by chemical reactions
16. An electrically neutral atom has electronic configuration 2,8,2. Its atomic number is ________. (a) 14   (b) 20   (c) 10   (d) 12
17. In a closed reversible reaction, the forward and backward rates become equal. The system has reached ________. (a) cessation of molecular collisions   (b) complete disappearance of reactants   (c) dynamic equilibrium   (d) a state with only products present
18. Which of the following pairs correctly matches a compound with its bonding description? (a) Cu metal — molecular covalent bonds only; NaCl — metallic bond   (b) NH₄⁺ formation — coordinate donation of an electron pair; NaCl — ionic attraction   (c) H₂ — ionic donation; NH₄⁺ — no electron pair   (d) NaCl — hydrogen bonds only; H₂ — metallic bond
19. As steam condenses to water, how does the average particle arrangement change? (a) gain energy and move farther apart   (b) turn into protons   (c) increase their number of electrons   (d) lose energy and come closer together
20. The main reason most atomic mass is concentrated in the nucleus is ________. (a) protons and neutrons are much more massive than electrons   (b) electrons have exactly the same mass as neutrons   (c) atomic mass comes only from empty space   (d) the nucleus occupies most of the atom's volume
21. Two chemically pure water samples show the same hydrogen-to-oxygen mass ratio. Which law is supported by this result? (a) the rule of variable atomic number   (b) the law of increasing pressure   (c) the law of constant composition   (d) the principle of changing valency
22. A factory seeks increased product yield from a reversible reaction. The most defensible basis for choosing pressure and temperature is ________. (a) the balanced equation, heat change and Le Chatelier's principle   (b) increasing reactor pressure regardless of gas stoichiometry   (c) using the highest temperature regardless of reaction enthalpy   (d) catalyst selection alone without equilibrium data
23. In which state do particles have high mobility but retain approximately fixed volume under ordinary conditions? (a) Solid   (b) Gas   (c) Plasma   (d) Liquid
24. For an atom with proton number 19 and mass number 39, the number of neutrons is ________. (a) 58   (b) 19   (c) 20   (d) 39
25. All of these changes involve gaining thermal energy except ________. (a) freezing liquid water   (b) subliming a solid   (c) melting ice   (d) evaporating water
26. Brass can be separated physically, whereas pure copper is a single element. Which description correctly classifies the two materials? (a) both are compounds   (b) brass is a compound; copper is a mixture   (c) both are heterogeneous mixtures   (d) brass is a mixture; copper is an element
27. A neutral particle contains 17 protons, 18 neutrons and 17 electrons. What is its net electrical charge? (a) zero   (b) +1   (c) +17   (d) −1
28. A shared electron pair between non-metal atoms is characteristic of ________. (a) the absence of any bond   (b) metallic bonding only   (c) gravitational attraction   (d) covalent bonding
29. Which of these statements about isotopes is NOT correct? (a) They have the same number of protons   (b) They must have different atomic numbers   (c) They belong to the same element   (d) They may have different mass numbers
30. The correct procedure for separating two miscible liquids with sufficiently different boiling temperatures requires ________. (a) Fractional distillation   (b) Magnetic separation   (c) Ordinary filtration of the liquid mixture   (d) Hand picking
31. For A + B ⇌ C, adding more A at constant temperature initially tends to ________. (a) remove all B immediately without reaction   (b) stop all collisions in the vessel   (c) make C disappear permanently   (d) favour formation of more C
32. A dry jar contains only pure sodium chloride. How should its contents be classified? (a) an element   (b) a mixture of two separate solids   (c) a compound   (d) a solution of salt in water
33. CO and CO₂ contain oxygen masses in a simple whole-number ratio for a fixed mass of carbon. Which law is illustrated? (a) the law of gravitation   (b) the rule of dilution   (c) the law of multiple proportions   (d) the principle of constant pressure
34. A sample has 24 g carbon and 4 g hydrogen. With C = 12 and H = 1, its empirical formula is ________. (a) CH₄   (b) CH₂   (c) C₂H   (d) CH
35. Why does a molten ionic substance often conduct electricity better than its solid form? (a) Its molecules lose all mass   (b) Its ions cease to exist on melting   (c) Its electrons become protons   (d) Its ions can move and carry charge in the melt
36. The main reason a reversible reaction is usually studied in a closed system is ________. (a) to remove the need for temperature measurement   (b) to guarantee that every reactant becomes product   (c) to prevent loss of substances that would disturb equilibrium   (d) to eliminate the reverse reaction
37. A reaction is exothermic in the forward direction. Raising temperature at equilibrium generally favours ________. (a) complete removal of all reactants   (b) the exothermic forward direction without exception   (c) the endothermic reverse direction   (d) a change in atomic numbers
38. Which is NOT a correct characteristic of a solid? (a) It takes the shape and volume of every container it enters   (b) It has relatively fixed shape   (c) Its particles are closely packed   (d) It generally resists compression
39. A particle has a relative mass close to one and no electrical charge. It is most likely ________. (a) a positron   (b) an electron   (c) a proton   (d) a neutron
40. Which observation is consistent with chemical equilibrium rather than the reaction having stopped? (a) The forward reaction occurs but no reverse reaction is possible   (b) Concentrations remain constant while both directions continue   (c) No reactant or product remains   (d) All molecules are stationary

SECTION B: THEORY (30 MARKS)
Instruction: Answer Question 1 and any other TWO questions. Each question carries 10 marks.

Question 1
(a) A compound has 24 g carbon and 4 g hydrogen. Derive its empirical formula (C=12, H=1). (6 marks)
(b) Explain two differences between a compound and a physical mixture. (4 marks)

Question 2
(a) An atom contains 17 protons, 18 neutrons and 17 electrons. Find its atomic and mass numbers. (4 marks)
(b) Explain how the arrangements of electrons in a sodium atom (2,8,1) and chlorine atom (2,8,7) support ionic bond formation. (6 marks)

Question 3
(a) For NaCl and a covalent molecular substance such as H₂, contrast their bonding mechanisms. (4 marks)
(b) Use the law of conservation of mass to explain why a sealed reaction of total reactant mass 18 g must produce a total product mass of 18 g. (6 marks)

Question 4
(a) For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), predict the effect of increased pressure and explain using gas-mole counts. (6 marks)
(b) State why adding a catalyst changes the time to equilibrium without changing its position. (4 marks)

Objective Marking Scheme
Question 1 – ✅ (b) CH₂
Question 2 – ✅ (c) chemically pure carbon dioxide
Question 3 – ✅ (d) relatively large spaces between gas particles
Question 4 – ✅ (b) oppositely charged ions held by electrostatic attraction
Question 5 – ✅ (c) Atoms of one element can exist as isotopes with different masses
Question 6 – ✅ (b) Electron
Question 7 – ✅ (c) Al₂O₃
Question 8 – ✅ (a) plasma
Question 9 – ✅ (a) proton number; neutron number
Question 10 – ✅ (c) Adding a suitable catalyst
Question 11 – ✅ (a) dissolved sugar passes with the solvent through filter paper
Question 12 – ✅ (d) sublimation
Question 13 – ✅ (b) 8 g
Question 14 – ✅ (d) the side with fewer gas molecules, producing more NH₃
Question 15 – ✅ (a) A compound has a fixed chemical composition; a mixture may vary in composition
Question 16 – ✅ (d) 12
Question 17 – ✅ (c) dynamic equilibrium
Question 18 – ✅ (b) NH₄⁺ formation — coordinate donation of an electron pair; NaCl — ionic attraction
Question 19 – ✅ (d) lose energy and come closer together
Question 20 – ✅ (a) protons and neutrons are much more massive than electrons
Question 21 – ✅ (c) the law of constant composition
Question 22 – ✅ (a) the balanced equation, heat change and Le Chatelier's principle
Question 23 – ✅ (d) Liquid
Question 24 – ✅ (c) 20
Question 25 – ✅ (a) freezing liquid water
Question 26 – ✅ (d) brass is a mixture; copper is an element
Question 27 – ✅ (a) zero
Question 28 – ✅ (d) covalent bonding
Question 29 – ✅ (b) They must have different atomic numbers
Question 30 – ✅ (a) Fractional distillation
Question 31 – ✅ (d) favour formation of more C
Question 32 – ✅ (c) a compound
Question 33 – ✅ (c) the law of multiple proportions
Question 34 – ✅ (b) CH₂
Question 35 – ✅ (d) Its ions can move and carry charge in the melt
Question 36 – ✅ (c) to prevent loss of substances that would disturb equilibrium
Question 37 – ✅ (c) the endothermic reverse direction
Question 38 – ✅ (a) It takes the shape and volume of every container it enters
Question 39 – ✅ (d) a neutron
Question 40 – ✅ (b) Concentrations remain constant while both directions continue

Theory Marking Scheme
Question 1
(a) Moles C=24/12=2 (2), H=4/1=4 (2); divide by 2 -> CH₂ (2). [6 marks]
(b) Compound fixed chemical ratio and requires chemical separation (2); mixture variable composition and physically separable (2). [4 marks]
Question 2
(a) Atomic number = 17 (2), mass number = 17+18 = 35 (2). [4 marks]
(b) Na transfers one outer electron and forms Na⁺ (2), Cl accepts one electron and forms Cl⁻ (2), opposite charges attract electrostatically (2). [6 marks]
Question 3
(a) NaCl formed by electron transfer and ion attraction (2); H₂ by sharing one electron pair (2). [4 marks]
(b) Atoms are rearranged, not destroyed or created (3); closed system retains all matter, so total products = 18 g (3). [6 marks]
Question 4
(a) Reactant gas moles=4 and products=2 (2); pressure shift to fewer gas particles/products (2); more ammonia at new equilibrium (2). [6 marks]
(b) Catalyst accelerates forward and reverse reactions (2); does not favour either equilibrium side or change equilibrium constant at same temperature (2). [4 marks]