Beatty 19.1 Alkanes WS1 2023 Answers 4E1

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E1 TOPIC: ALKANES (WORKSHEET 1) Learning Objectives: (a) Describe an homologous series as a group of compounds with a general formula, similar chemical properties and showing a gradation in physical properties as a result of increase in the size and mass of the molecules, e.g. melting and bo iling points; viscosity; flammability. (b) Describe the alkanes as an homologous series of saturated hydrocarbons with the general formula CnH2n+2. (c) Draw the structures of branched and unbranched alkanes, C1 to C 4, and name the unbranched alkanes, methane to butane. (d) Describe the properties of alkanes (exemplified by methane) as being generally unreactive except in terms of burning and substitution by chlorine. Multiple-Choice Questions 1 Decane is an alkane containing ten ca rbon atoms per molecule. What is its molecular formula? A C10H18 B C10H20 C C10H22 D C10H24 ( C ) 2 The structure of compound J is shown. Which row describes J? saturated hydrocarbon A no no B no yes C yes no D yes yes ( C ) 3 Methane is the first member of the alkane homologous series. Which ro w describes the changes in flamm ability and the size of the molecules in th e alkane homologous series from methane to propane? flammability size of molecules A decreases decreases B decreases increases C increases decreases D increases increases ( B )

2 4 Which of these properties of alkanes decreases with increasing relative molecular mass of the alkane? A melting point B flammability C density D boiling point ( B ) 5 Which statement about a homologous series is correct? A The boiling point increases with decreasing relative molecular mass. B The members have the same empirical formula (formula showing the number of atoms in the simplest ratio). C The members have similar chemical properties. D The relative molecular masses of consecutive members differ by 12. ( C ) 6 Nonane is an alkane present in petrol. What are the products formed when nonane is completely burnt in air? A carbon dioxide and hydrogen B carbon monoxide and water C carbon dioxide and water D carbon dioxide, carbon monoxide and water ( C ) 7 What are the main products when chlorine reacts with methane? A chloromethane and hydrogen B chloromethane and hydrogen chloride C dichloromethane and hydrogen D trichloromethane and carbon chloride ( B ) 8 The diagrams show the structures of three compounds. Which compounds can be products of substitution reactions of ethane with chlorine? A 1 only B 2 only C 1 and 3 only D 1, 2 and 3 ( D ) 9 100 cm 3 of methane is bu rned in 1 50 cm 3 of oxygen. When cooled to room temperature, what could be the resulting mixture of gases? A CH4, CO, CO2 B CH4, CO, H2O C CH4, CO2, O2 D CO2, H2, O2 ( A )

3 Structured Questions 10 Briefly explain what is meant by the following terms: (a) a saturated hydrocarbon, A saturated hydrocarbon contains carbon and hydrogen atoms only, with only carbon-carbon single bonds in the compound. (b) a homologous series, A homologous series is a family of organic compounds which has the same functional group , each successive member differing in composition by a −CH2− group. (c) a functional group. A functional group is an atom or group of atom s responsible for the chemical properties of an organic compound. 11 (a) Name the compound with the formula C3H8. propane (b) Write a balanced chemical equation for the complete combustion of C3H8 in air. C3H8 + 5O2 → 3CO2 + 4H2O (c) Name two products of the combustion, other than water if the supply of oxygen is restricted. carbon monoxide (incomplete combustion) / carbon dioxide (Complete combustion) / carbon (from incomplete combustion) 12 The alkanes are an homologous series of saturated hydrocarbons. (a) State the general formula of alkanes. CnH2n+2 (b) One property of a homologous series is that its members have the same general formula. State two other properties of a homologous series. Each successive member differs by a −CH2− group. All the members have the same functional group. Members of a homologous series have similar chemical properties but different physical properties.

4 (c) Name the type of reaction that occurs when an alkane reacts with chlorine. substitution (d) Write a balanced equation for the reaction between methane and chlorine. CH4 + Cl2 → CH3Cl + HCl 13 Alkanes are saturated compounds which do not react with most chemicals. However t hey do undergo substitution reactions with chlor ine in the presence of sunlight to form a mixture of chloroalkanes. (a) Complete the following chemical equations involving methane. Draw the structural formula of the chloroalkane formed at each stage. The one for methane is given. (i) CH4 + Cl2 heat + light CH3Cl + HCl (ii) CH3Cl + Cl2 heat + light CH2Cl2 + HCl (iii) CH2Cl2 + Cl2 heat + light CHCl3 + HCl (iv) CHCl3 + Cl2 heat + light CCl4 + HCl methane (i) monochloromethane (ii) dichloromethane (iii) trichloromethane (iv) tetrachloromethane (b) Using one example from the above, explain what is meant by a substitution reaction. In the above reaction, a hydrogen atom from methane is substituted by a chlorine atom to form monochloromethane. A substitution reaction is a reaction in which an atom or a group of atoms is replaced by atoms of other elements.

5 (c) Predict whether methane will react faster or slower with bro mine. Explain yo ur answer. Methane will react slower with bromine because bromine is less reactive than chlorine. 14 The following apparatus is set up to study the products formed when methane is burnt. At the st art of the experiment, the U -tube is empty a nd the liquid Y is present in the boiling tube. The teacher light s a jet of methane and then turns on a suction pump to dr aw the combustion gases through the apparatus. (a) Name liquid X. water (b) How can you prove that liquid X is pure? Determine the bo iling point o f the l iquid. If the liquid boils at a fixed temperature, the liquid is pure. If the l iquid boils over a range of temperatures, the liquid is impure. (c) Liquid Y is present in the tube to prov ide a test for carbon dioxide. Name liquid Y and describe how it would change during the investigation. identity of liquid Y limewater / calcium hydroxide changes to liquid Y during the experiment Colourless liquid Y turns to form a white precipitate. (d) Write a chemical equation for the reaction in this experiment. CH4 + 2O2 → CO2 + 2H2O

6 15 The table shows some information about the homologous series of a class of organic compounds called ether. name chemical formula full structural formula dimethyl ether H3COCH3 diethyl ether H5C2OC2H5 dipropyl ether H7C3OC3H7 (a) Fill in the table to show the name, chemi cal formula and full structural formula of the ether that occurs between dimethyl ether and dipropyl ether in the homologous series. (b) Explain how you can tell that t hese m olecules are from the same homologous series. These molecules have the same functional group ─C─O─C─ same general formula of C nH2n+2O where n is an even number / CnH2n+1OCnH2n+1. (c) Describe two differences in