Secondary 3 Combined Science Chemistry Materials Quiz

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Secondary 3 Combined Science Quiz - Chemistry Materials

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 45

Duration: 60 Minutes
Total Marks: 45 Marks

Instructions:

• Answer all questions.
• For calculation questions, show all working clearly.
• Use scientific terminology and balanced chemical equations where required.

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Section A: Fundamental Concepts (Questions 1-5)

1. State the purpose of using a solvent in paper chromatography. [1]

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2. Define the term 'isotopes' in relation to atomic structure. [1]

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3. State one property of ionic compounds and explain it in terms of bonding. [2]

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4. Which of the following is a characteristic of a covalent bond? [1] (a) Transfer of electrons from metal to non-metal (b) Sharing of electrons between two non-metals (c) Attraction between positive ions and a sea of electrons (d) Strong attraction between oppositely charged ions Answer: ________

5. Describe the structure of a giant covalent lattice using diamond as an example. [2]

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Section B: Chemical Reactions & Extraction (Questions 6-13)

6. Write the balanced chemical equation for the roasting of zinc blende (zinc sulfide). Include state symbols. [2]

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7. In the extraction of zinc, carbon is used to reduce zinc oxide. Write the balanced chemical equation for this step. Include state symbols. [2]

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8. Calculate the mass of zinc extracted if 100g of zinc oxide is completely reduced by carbon. (Relative atomic masses: Zn = 65, O = 16). [2]

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9. A student reacts 2.0g of solid calcium carbonate with dilute hydrochloric acid. (a) Write the balanced chemical equation for this reaction. [2]

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   (b) Write the ionic equation for the reaction. [2]

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10. Calculate the volume of carbon dioxide gas produced at room temperature and pressure (rtp) from the reaction in Question 9. (Molar volume of gas = 24 dm³/mol). [2]

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11. State the observation made when dilute nitric acid is added to solid zinc carbonate. [1]

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12. Explain why zinc is extracted using carbon rather than by electrolysis. [2]

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13. Compare the reactivity of zinc and copper based on their positions in the reactivity series. [1]

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Section C: Analytical Chemistry & Applications (Questions 14-20)

14. In a chromatography experiment, the solvent front traveled 8.0 cm and a dye spot traveled 3.2 cm. Calculate the $R_f$ value of the dye. [2]

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15. A chromatogram shows that a sample of ink contains three different dyes. Explain why the dyes separate into different spots. [2]

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16. An athlete's urine sample is tested for banned substances B1 and B2. The sample shows a spot at the same height as B1 but not B2. State the conclusion. [1]

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17. Describe how you would determine if a colorless gas produced from a carbonate reaction is carbon dioxide. [2]

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18. Explain why graphite is used as a lubricant while diamond is used in cutting tools, referring to their structures. [3]

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19. A sample of an unknown metal oxide is reduced by carbon. The resulting metal is found to be zinc. (a) Identify the original ore. [1]

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    (b) State the type of reaction that occurs during the reduction step. [1]

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20. Suggest one way to improve the accuracy of the $R_f$ value measurement in paper chromatography. [1]

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Answer Key - Secondary 3 Combined Science Quiz (Chemistry Materials)

1. To dissolve the sample/solutes so they can be carried up the paper by the solvent. [1]
2. Atoms of the same element with the same number of protons but different numbers of neutrons. [1]
3. High melting point [1]; due to strong electrostatic forces of attraction between oppositely charged ions in a giant lattice. [1]
4. (b) [1]
5. Each carbon atom is covalently bonded to four other carbon atoms [1], forming a rigid 3D tetrahedral structure. [1]
6. $2\text{ZnS(s)} + 3\text{O}_2\text{(g)} \rightarrow 2\text{ZnO(s)} + 2\text{SO}_2\text{(g)}$ [2]
7. $\text{ZnO(s)} + \text{C(s)} \rightarrow \text{Zn(s)} + \text{CO(g)}$ or $2\text{ZnO(s)} + \text{C(s)} \rightarrow 2\text{Zn(s)} + \text{CO}_2\text{(g)}$ [2]
8. Molar mass $\text{ZnO} = 65+16 = 81\text{g/mol}$. Moles $\text{ZnO} = 100/81 = 1.23\text{ mol}$. Mass $\text{Zn} = 1.23 \times 65 = 80.1\text{g}$. [2]
9. (a) $\text{CaCO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow \text{CaCl}_2\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ [2] (b) $\text{CaCO}_3\text{(s)} + 2\text{H}^+\text{(aq)} \rightarrow \text{Ca}^{2+}\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ [2]
10. Molar mass $\text{CaCO}_3 = 100\text{g/mol}$. Moles = $2.0/100 = 0.02\text{ mol}$. Volume = $0.02 \times 24 = 0.48\text{ dm}^3$ (or $480\text{ cm}^3$). [2]
11. Effervescence / Bubbles of colorless gas evolved. [1]
12. Zinc is less reactive than aluminum/magnesium [1], so it can be reduced by a cheaper reducing agent like carbon. [1]
13. Zinc is more reactive than copper. [1]
14. $R_f = 3.2 / 8.0 = 0.4$ [2]
15. Different dyes have different solubilities in the solvent [1] and different affinities/attractions to the chromatography paper. [1]
16. Banned substance B1 is present in the athlete's urine. [1]
17. Bubble the gas into limewater [1]; the limewater turns milky/cloudy. [1]
18. Graphite: Layers can slide over each other due to weak forces between layers [1.5]. Diamond: Rigid 3D structure with strong covalent bonds in all directions [1.5].
19. (a) Zinc blende ($\text{ZnS}$) or Zincite ($\text{ZnO}$). [1] (b) Reduction. [1]
20. Use a pencil to mark the start and end lines precisely / Use a ruler for accurate measurement. [1]