Carbon and its Compounds

Carbon makes up only about 0.02% of the Earth's crust as minerals and 0.03% of the atmosphere as carbon dioxide, yet it forms millions of compounds, including fuels, plastics, medicines and the molecules of life. In this chapter you will learn why carbon, with four valence electrons, neither gains nor loses electrons but shares them to form covalent bonds, and how to draw electron dot structures for molecules such as H2, O2, N2, CH4 and H2O. Two special properties, catenation and tetravalency, explain the huge number of carbon compounds, including saturated and unsaturated hydrocarbons, chains, branches, rings and isomers. You will learn about functional groups (halo, alcohol, aldehyde, ketone and carboxylic acid), homologous series and IUPAC naming. You will study combustion, oxidation, addition and substitution reactions, and the properties of two important compounds, ethanol and ethanoic acid, including esterification. Finally, you will see how soaps and detergents clean by forming micelles, and why soaps do not work well in hard water.

Detailed Worksheet: Carbon and its Compounds Section A - Definitions (10 marks) 1. What is a covalent bond? Why does carbon form covalent bonds rather than ionic bonds? (2 marks) 2. Define catenation and tetravalency. How do these properties explain the large number of carbon compounds? (2 marks) 3. What are structural isomers? Draw the structures of the two isomers of butane (in words or with C and H symbols). (2 marks) 4. Define a homologous series and state two of its characteristics. (2 marks) 5. What is a functional group? Name the functional groups present in ethanol and ethanoic acid. (2 marks) Section B - Calculations and Applications (15 marks) 6. Count the number of covalent bonds in (i) propane, C3H8 (ii) pentane, C5H12 (iii) cyclopentane, C5H10. Show that an alkane CnH2n+2 has 3n + 1 covalent bonds. (3 marks) 7. Write balanced chemical equations for (i) the complete combustion of methane (ii) the complete combustion of ethanol (iii) the chlorination of methane in sunlight (first step). (3 marks) 8. The molecular masses of the first three members of the alkane series are 16 u, 30 u and 44 u. What is the difference between successive members? Write the formulae and predict the molecular mass of the fifth member. (C = 12, H = 1) (3 marks) 9. Calculate the mass of carbon dioxide produced when 16 g of methane burns completely in oxygen. Write the balanced equation. (C = 12, H = 1, O = 16) (3 marks) 10. In the esterification of ethanoic acid with ethanol, 60 g of ethanoic acid reacts completely with 46 g of ethanol. Write the balanced equation and calculate the mass of ethyl ethanoate formed. (C = 12, H = 1, O = 16) (3 marks) Section C - Diagrams (10 marks) 11. Draw the electron dot structures of (i) a molecule of nitrogen (ii) a molecule of methane (iii) a molecule of ethene. Show the number of shared electron pairs in each. (4 marks) 12. Draw a labelled diagram of the activity to show esterification: ethanol and glacial ethanoic acid with a few drops of conc. sulphuric acid in a test tube warmed in a water bath. State the observation. (3 marks) 13. Draw a labelled diagram showing the formation of a micelle by soap molecules around an oily dirt particle in water, marking the ionic (hydrophilic) end and the hydrocarbon (hydrophobic) tail. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain why diamond is the hardest natural substance and a non-conductor, while graphite is soft, slippery and a good conductor, though both are pure carbon. Name a third allotrope of carbon and describe its structure. (5 marks) 15. A compound C (molecular formula C2H4O2) reacts with Na metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in the presence of an acid forms a sweet-smelling compound S (molecular formula C3H6O2). On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back the alcohol A and R. Identify C, R, A and S and write the chemical equations for the reactions involved. (5 marks) 16. Explain why soap does not form lather easily with hard water, while detergents do. Write the names of the ions responsible for hardness. Why are some detergents harmful to the environment, and how have newer detergents tried to address this? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Write structural formulae and balanced equations wherever asked. Use IUPAC names along with common names where appropriate.