20A Molecular Structures - Assignment Answer Key

Anglo-Chinese School (Barker Road) A Methodist Institution Founded in 1886 CHEMISTRY DEPARTMENT OF SCIENCE Name: ANSWERS ( ) Class: SEC 4 OC: MOLECULAR STRUCTURES – ASSIGNMENT ALEX LEE/2010 PAGE 1 OF 5 PURE/COMBINED/N-LEVEL Multiple-Choice Questions [20 Marks] TOTAL SCORE / 30 Write in your selected answer for the multiple-choice questions in the boxes provided. 1 2 3 4 5 6 7 8 9 10 C C A B C B C C B C 11 12 13 14 15 16 17 18 19 20 C B B C A A C A A C 1. All members of an homologous series A contain the same number of bonds. B contain the same number of carbon atoms. C share a general formula. D share the same melting and boiling points. 2. Which of the following statements about an homologous series is false? A Members of a homologous series contain a different number of hydrogen atoms. B Members of a homologous series have different melting and boiling points. C Members of a homologous series share the same empirical formula. D Members of a homologous series undergo similar chemical reactions. 3. Down a homologous series, the boiling points of each successive member increases because A the intermolecular forces between the molecules increases. B the number of hydrogen atoms increases. C there are a larger number of bonds to be broken. D there covalent bonds are get increasingly stronger. 4. Which of the following is not a trend across a homologous series, in order of increasing number of carbon atoms? A Increasing density. C Increasing mass. B Increasing flammability. D Increasing viscosity. 5. Which of the following is a possible general formula for carboxylic acids? A CnH2n+1COH B CnH2nCO2H C CnH2nO2 D CnHn+1CO2H

ALEX LEE/2010 PAGE 2 OF 5 6. What is the molecular formula for propanoic acid and butanol? propanoic acid butanol A C2H5COOH C3H7OH B C2H5COOH C4H9OH C C3H7COOH C3H8O D C3H7COOH C4H10O 7. Which of the following correctly states the molecular formula, empirical formula and simplified structural formula of propene? molecular formula empirical formula structural formula A CH2 C3H6 CH2CHCH3 B CH2CHCH3 CH2 C3H6 C C3H6 CH2 CH2CHCH3 D C3H6 CH2CHCH3 CH2 8. Cycloalkanes are compounds with a ‘ring’ carbon chain. Two examples of cycloalkanes are cyclopentane and cyclohexane: cyclopentane cyclohexane Which of the following correctly shows the general formula for alkanes, alkenes and cycloalkanes? alkanes alkenes cycloalkanes A CnH2n CnH2n CnH2n+2 B CnH2n CnH2n+2 CnH2n C CnH2n+2 CnH2n CnH2n D CnH2n+2 CnH2n CnH2n+2 9. Which of the following statements about the alkene homologous series is true? A All members are gaseous at room temperature. B All members have the same empirical formula. C All members have the same molecular mass. D All members have the same structural formula. 10. Which of the following statements about the alcohol homologous series is true? A All members are hydrocarbons. B All members are liquid at room temperature. C All members have different empirical formulae. D All members have different chemical properties.

ALEX LEE/2010 PAGE 3 OF 5 11. A member of a homologous series has a molecular formula of C8H10. What is the molecular formula of the preceding member (i.e. the member just before it)? A C4H10 B C6H9 C C7H8 D C7H9 12. A member of a homologous series has a formula of C2H5N. What is the formula of the following member (i.e. the member just after it)? A C3H6N B C3H7N C C3H7N2 D C4H10N2 13. Which one of the following molecules contains a C=C bond? A C3H8 B C4H8 C C2H6O D CH3COOH 14. Eicosapentaenoic acid is a type of fatty acid and has a formula of C19H29COOH. How many C=C bonds are there in its structure? A none B three C five D ten 15. The structure of an organic compound X is shown below. C CC H HH HH C H HO OH C CC H HH HH C H HO OH Identify X. A butanoic acid B butanol C propene D propanoic acid 16. A molecule has the formula C4H8O2. It follows that the molecule A combusts completely to produces carbon dioxide and water only. B contains a C=C double bond in its structure. C must be miscible with water and other polar solvents. D must have a –COOH functional group in its structure. 17. Which of the following statements is false? A Both ethane and ethene are insoluble in water. B Both ethanol and ethanoic acid are soluble in water. C Ethane contains only C–H bonds in its structure. D Ethanoic acid contains a double bond in its structure. 18. Which of the following statements is true? A Any compound with a C=C bond will have chemical properties of an alkene. B Members of a homologous series must share the same empirical formula. C Molecular size is the only factor affecting the boiling point of an organic compound. D The first four alcohols are gaseous at room temperature and pressure.

ALEX LEE/2010 PAGE 4 OF 5 19. The structure of an organic compound Y is shown below. C CC H HO H H H HCHH H H C CC H HO H H H HCHH H H Which of the following best describes Y? A Y is an alcohol. B Y is an alkane. C Y is both an alcohol and an acid. D Y is both an alkene and an alcohol. 20. The structure of an organic compound Z is shown below. COH C H C H C OO HO COH C H C H C OO HO Which of the following best describes Z? A Z has the properties of an alkene, an alcohol and an acid. B Z has the properties of both an alcohol and an acid. C Z has the properties of both an alkene and an acid. D Z has the properties of both an alkene and an alcohol. Structured Questions [10 Marks] 21. Amines refer to a homologous series of molecules with the –NH2 group in its structure. The first member of this homologous series is methylamine, as shown: (a) In the space below, write down the name and structural formula of the next member in the homologous series. [2] ethylamine

ALEX LEE/2010 PAGE 5 OF 5 (b) (i) State the general formula for this homologous series. [1] CnH2n+1NH2 or CnH2n+3N (ii) Hence state the formula of the amine with 28 atoms in its structure. [1] C8H17NH2 or C8H19N 22. (a) Define the term ‘homologous series’. [2] It is a group/family of organic compounds which have the same functional group, share a general formula and show a gradation in physical properties. (b) Explain what is meant by a ‘functional group’. [1] It is an atom or group of atoms within the structure of an organic molecule which gives the compound its characteristic properties. 23. Complete the table below. [3] molecule name simplified structural formula full structural formula ethanoic acid CH3COOH CH C H HO OH CH C H HO OH methylpropane CH3CH(CH3)CH3 propene CH2CHCH3 or CH3CHCH2 H CC HC H H H H H CC HC H H H H chlorobutane CH3CHClCH2CH3 C CC H HH HH C H Cl H H H C CC H HH HH C H Cl H H H END