Organic molecules: Grade 12 Past Paper Questions

QUESTION 7: Study the flow diagram below. An organic compound Z is produced from compound X using Reaction I and Reaction II. Compound X is converted (Reaction I, using concentrated H₂SO₄) into compound Y, which is then converted (Reaction II) into compound Z, a dihaloalkane. 7.1 Name the functional group of compound X. 7.2 Write down the IUPAC name of compound X. 7.3 Name the homologous series of the organic product that would be produced if compound X were now treated with a carboxylic acid in the presence of hot, concentrated sulphuric acid. 7.4 Identify the homologous series of compound Y. 7.5 Name the type of addition reaction represented by Reaction II. 7.6 Using structural formulae, write down the balanced chemical equation for Reaction II.

QUESTION 4: Study the flow diagram below. Compounds A, B, C, D and E are organic compounds, related through Reactions 1–6; the diagram includes Br₂ and 1-bromobutane among the reaction species. Reaction 6 is an addition reaction. 4.1 Write down the: 4.1.1 type of reaction represented by Reaction 1; 4.1.2 reaction condition for Reaction 1. 4.2 In Reaction 3, compound C reacts with HCOOH in the presence of concentrated H₂SO₄. Write down the: 4.2.1 structural formula of compound C; 4.2.2 type of reaction represented by Reaction 3; 4.2.3 IUPAC name of compound D. 4.3 Write down TWO terms for the type of reaction represented by Reaction 2. 4.4 Compound C can be converted back to compound B. Write down the formula or name of the inorganic reagent needed for this conversion. 4.5 Compounds B and C can be converted to compound E. 4.5.1 Write down ONE term for the type of organic reaction for BOTH Reactions 4 and 5. Besides heat, write down a reaction condition for: 4.5.2 Reaction 4; 4.5.3 Reaction 5. Consider Reaction 4: 4.5.4 Using structural formulae, write down the balanced equation.

QUESTION 3: 3.1 Consider the diagram of two methanol molecules shown below; I and II represent forces in the molecules. Choose I OR II for EACH of the following: 3.1.1 the force which, when broken or overcome, results in a chemical change; 3.1.2 the force that requires more energy to overcome; 3.1.3 the force responsible for the boiling point of methanol. 3.2 In an investigation, the boiling points of four compounds, A (methanol), B (ethanol), C (butan-1-ol) and D (butan-2-ol), are compared. The boiling point of C is given as 117,7 °C, and the boiling point of D is indicated as X. 3.2.1 Define the term boiling point. The boiling points of compounds A, B and C are compared. 3.2.2 With reference to molecular structure, give the reason why this is a fair comparison. 3.2.3 Name the intermolecular force responsible for the difference in these boiling points. 3.2.4 Give a reason for the increase in boiling points in terms of the molecular structure of the compounds. The boiling points of compounds C and D are compared. 3.2.5 Will X, the boiling point of D, be GREATER THAN, LESS THAN or EQUAL TO 117,7 °C? Fully explain the answer.

QUESTION 5: The letters A to F in the table below represent organic compounds, given as structural formulae or names, including compound C, pentan-2-one, and compound D, methyl propanoate (CH₃CH₂COOCH₃). 5.1 Define the term homologous series. 5.2 Consider the organic compound B. Write down the: 5.2.1 homologous series to which this compound belongs; 5.2.2 IUPAC name of the functional isomer of this compound. 5.3 Write down the: 5.3.1 IUPAC name of compound E; 5.3.2 general formula of the homologous series to which compound A belongs. 5.4 Write down the LETTER(s) of the compound(s) that represent(s): 5.4.1 the positional isomers; 5.4.2 an ester.

QUESTION 5: The letters A to F in the table below represent six organic compounds, given as structural formulae or names — including ethyl propanoate and 2-methylbutan-2-ol, (CH₃)₂C(OH)CH₂CH₃, among those shown. 5.1 Define homologous series. 5.2 To which homologous series does compound B belong? 5.3 Draw the structural formula of compound B. 5.4 Write down the LETTER that represents the following: 5.4.1 an unsaturated hydrocarbon; 5.4.2 a compound with the general formula CₙH₂ₙO. 5.5 Write down: 5.5.1 the IUPAC name of compound A; 5.5.2 the IUPAC name of compound D; 5.5.3 the balanced equation, using MOLECULAR FORMULA, of the complete combustion of compound E.

QUESTION 7: 7.1 The following equation represents the cracking of a hydrocarbon at high temperature and pressure: C₁₁H₂₄ → 2C₂H₄ + Y + C₄H₁₀. Draw the structural formula of compound Y. 7.2 The flow diagram below shows the preparation of different organic compounds using compound P, which has the general formula CₙH₂ₙ₊₂. Compound P reacts (Reaction 1) to form 2-chlorobutane and an inorganic compound, and further reactions (Reaction 2, an elimination reaction, and Reaction 3, involving concentrated KOH) produce compounds Q and R (major product). 7.2.1 Write down ONE reaction condition for Reaction 1. 7.2.2 Is 2-chlorobutane a PRIMARY, SECONDARY, or TERTIARY haloalkane? Explain your answer. 7.2.3 Write down the balanced equation, using structural formulae, for Reaction 3. 7.3 Reaction 2, in the flow diagram above, is an elimination reaction during which the organic compound Q and TWO inorganic compounds are formed. Write down: 7.3.1 the NAME of this type of elimination reaction; 7.3.2 the IUPAC name of Compound Q; 7.3.3 the FORMULA of EACH inorganic product formed during Reaction 2.

QUESTION 6: The boiling points of various primary straight-chain alcohols are provided in the table below, including butan-1-ol (118 °C) and pentan-1-ol (138 °C). 6.1 Write down the NAME of the functional group of alcohols. 6.2 Define the term boiling point. 6.3 Which ONE of the alcohols mentioned above is the LEAST flammable at room temperature? Explain your answer by referring to vapour pressure and risk of ignition. 6.4 Use the information in the table above to answer the following questions. 6.4.1 On the graph paper provided, draw a graph of boiling point versus the number of carbons in each alcohol. 6.4.2 State the trend shown on the graph. 6.4.3 Explain your answer in 6.4.2 by referring to the TYPE and STRENGTH of the intermolecular forces involved.

QUESTION 7: The flow diagram below shows the preparation of different organic compounds using CH₃CH=CH₂ as a starting reagent. X, Y, Z and P represent different organic reactions; CH₃CHClCH₃ (2-chloropropane) appears as one of the products in the scheme. 7.1 To which homologous series does CH₃CH=CH₂ belong? 7.2 Write down the: 7.2.1 type of addition reaction represented by X; 7.2.2 structural formula and IUPAC name of the alcohol produced during Reaction P; 7.2.3 type of reaction of which Y is an example. 7.3 For Reaction Z, write down: 7.3.1 the NAME of the inorganic product formed; 7.3.2 TWO reaction conditions needed; 7.3.3 a balanced equation for the production of the alkene, using CONDENSED STRUCTURAL FORMULAE.

QUESTION 5: The letters A to E in the table below represent organic compounds, including propyl ethanoate among the structures shown. 5.1 Write down the letter(s) that represent: 5.1.1 a compound with the general formula CₙH₂ₙ₊₁OH; 5.1.2 a haloalkane; 5.1.3 a product of the reaction between an alcohol and a carboxylic acid. 5.2 For compound C, write down the: 5.2.1 type of alcohol it is, and give a reason for the answer; 5.2.2 IUPAC name; 5.2.3 name of its functional group. 5.3 Consider the functional isomer of propyl ethanoate. 5.3.1 Define the term functional isomers. 5.3.2 Write down the IUPAC name of its functional isomer. 5.4 Write down the structural formula of compound E.

QUESTION 7: The vapour pressure versus temperature graph below was obtained for FOUR straight-chain (unbranched) compounds with FIVE carbon atoms in their structures, A, B, C and D, which belong to different homologous series — carboxylic acids, aldehydes, alkanes and alcohols, randomly assigned. The boiling point of the saturated hydrocarbon is 36,3 °C. 7.1 Define the term vapour pressure. 7.2 Write down the: 7.2.1 value represented by x on the graph; 7.2.2 CONDENSED STRUCTURAL FORMULA of the SATURATED HYDROCARBON; 7.2.3 NAME of the FUNCTIONAL GROUP of compound B. 7.3 Which compound (A or B) has STRONGER INTERMOLECULAR FORCES? Give a reason for the answer. 7.4 Explain the difference in boiling points of compound C and D.

QUESTION 6 (continued): The table on page 7, showing four organic compounds A to D from different homologous series — including methyl ethanoate and propanone, CH₃COCH₃, among them — is redrawn below for easy reference. 6.3 For organic compound A, write down the: 6.3.1 IUPAC NAME; 6.3.2 type of haloalkane (PRIMARY, SECONDARY or TERTIARY), giving a reason for the answer. 6.4 Draw the STRUCTURAL FORMULA of the ORGANIC ACID used to form compound B. 6.5 Write down a balanced chemical equation, using MOLECULAR FORMULA, for the complete combustion of compound C. 6.6 Consider the organic compound D to answer the questions below. 6.6.1 Write down the name given to its functional group. 6.6.2 Draw the structural formula of the FUNCTIONAL ISOMER of compound D. 6.6.3 Calculate the percentage composition of OXYGEN atoms in the compound.

QUESTION 8: Consider the incomplete equations for Reactions I to III below. P, R and S are organic compounds. Study the equations and answer the questions that follow. Reaction I: 2-bromopropane + NaOH → P + Q + H₂O. Reaction II: P + H₂O → R (minor product). Reaction III: R + S → propyl propanoate + T. 8.1 Write down the: 8.1.1 NAME of the ELIMINATION reaction represented by Reaction I; 8.1.2 ONE reaction condition for Reaction I; 8.1.3 MOLECULAR FORMULA of compound P; 8.1.4 CHEMICAL FORMULA or CHEMICAL NAME of compound Q. 8.2 For Reaction II, write down the: 8.2.1 type of reaction; 8.2.2 chemical formula of the INORGANIC ACID required during this reaction; 8.2.3 balanced chemical equation using STRUCTURAL FORMULAE. 8.3 For Reaction III, write down the: 8.3.1 type of reaction; 8.3.2 IUPAC NAME of compound S; 8.3.3 CHEMICAL FORMULA or CHEMICAL NAME of compound T.

QUESTION 2: The letters A to H in the table below represent organic compounds, including butan-1-ol among them; compound H is given as a structural diagram of a four-carbon alcohol. 2.1 Consider compound H. Is this a PRIMARY, SECONDARY or TERTIARY alcohol? Explain the answer. 2.2 Write down the letter that represents each of the following: 2.2.1 a ketone; 2.2.2 a MOLECULAR FORMULA of a hydrocarbon; 2.2.3 a reactant in the preparation of compound C. 2.3 Write down the STRUCTURAL formula of: 2.3.1 compound D; 2.3.2 the FUNCTIONAL group of compound F; 2.3.3 the FUNCTIONAL isomer of compound G with a prefix of 4-methyl. 2.4 Write down the IUPAC name of: 2.4.1 compound D; 2.4.2 compound G. 2.5 Consider compounds E and H. 2.5.1 Identify the type of isomer. 2.5.2 Define this type of isomer.

QUESTION 4: The flow diagram below shows how an alkene can be used to prepare other organic compounds. The letters J to N represent various organic reactions; the diagram includes Compound Q and Compound R (major product), with a minor product also formed. 4.1 Is an alkene a SATURATED or UNSATURATED hydrocarbon? Explain the answer. 4.2 Write down the type of reaction represented by: 4.2.1 J; 4.2.2 K; 4.2.3 M. 4.3 Write down the STRUCTURAL FORMULA of compound R. 4.4 For Reaction N, write down: 4.4.1 the type of addition reaction; 4.4.2 two reaction conditions; 4.4.3 the IUPAC name of the alcohol that forms. 4.5 Write down the IUPAC name of an isomer of butane. 4.6 Use STRUCTURAL formulae to write down a balanced equation for Reaction L.

QUESTION 1 (multiple-choice): 1.4 Consider the molecular formula of an organic compound (given below). The name of the homologous series that the above compound belongs to is a/an ...: A. ketone. B. alcohol. C. aldehyde. D. carboxylic acid. 1.5 Given the following four organic molecules: ethanal, ethanol, ethanoic acid, and ethane. Which ONE is CORRECT when the above compounds are arranged in their decreasing order of vapour pressure? (Four orderings of these four compounds are given as answer options.) 1.6 Which ONE of the following reaction types will be used to prepare ethene and propane from pentane under high temperatures and pressures? A. Combustion. B. Esterification. C. Thermal cracking. D. Photosynthesis.

QUESTION 1: MULTIPLE-CHOICE QUESTIONS. Various options are provided as possible answers to the following questions; choose the correct letter (A–D). 1.1 Consider the following reaction: CH₃(CH₂)₃CH₃ → CH₄ + 2CH₂=CH₂. This is an example of a/an ... reaction. A. cracking. B. addition. C. hydrolysis. D. substitution. 1.2 Four organic compounds (I to IV) are shown below as branched structural formulas. Which of the compounds above have the same IUPAC name? (Four answer options pairing different compounds are given.)

5.5 When making an ester, 60 g of propan-1-ol reacts with excess ethanoic acid to produce 90,78 g of the ester. The balanced equation for the reaction is: C₃H₇OH(l) + CH₃COOH(aq) → C₅H₁₀O₂(l) + H₂O. Write down the: 5.5.1 structural formula of the ester produced; 5.5.2 IUPAC name of the ester; 5.5.3 name or formula of the catalyst used. 5.6 Calculate the percentage purity of propan-1-ol. QUESTION 6: Experiments 1 and 2 are performed to determine the boiling points of carboxylic acids and alcohols. The results obtained are shown in the table below: Experiment 1 — methanoic acid, molecular mass 46 g·mol⁻¹, boiling point 100,8 °C; ethanol, molecular mass 46 g·mol⁻¹, boiling point 78,4 °C. Experiment 2 — propanoic acid, molecular mass 74 g·mol⁻¹, boiling point 141,2 °C; butan-1-ol, molecular mass 74 g·mol⁻¹, boiling point 117,7 °C. 6.1 Write down the property of alcohols which could make an experiment dangerous. 6.2 Write down the LETTERS of TWO compounds which are alcohols. 6.3 What conclusion can be drawn from the results of these two experiments? 6.4 Predict how the vapour pressure of compounds A and B will compare. 6.5 From the table above, the boiling point of the carboxylic acid in Experiment 2 is higher than the boiling point of the carboxylic acid in Experiment 1. Explain this observation by referring to the molecular structure, intermolecular forces and energy.

QUESTION 1 (multiple-choice, continued): 1.4 Consider the organic compounds (I to IV) shown below, structural formulas of alkenes with the carbon–carbon double bond in different positions. Which of the compounds above are positional isomers? A. I and II. B. I and III. C. I and IV. D. II and III. 1.5 In which one of the following alternatives are the three compounds — pentane, pentan-1-ol and pentanoic acid — listed in order of their increasing vapour pressure? (Four orderings of these three compounds are given as options; option D reads: Pentan-1-ol; Pentanoic acid; Pentane.) 1.6 An organic compound X has the molecular formula C₄H₈O₂. When X is heated with an excess of ethanol in the presence of concentrated sulfuric acid, a sweet-smelling compound forms. When compound X reacts with sodium carbonate solution, carbon dioxide is produced. Which ONE of the following is the IUPAC name of compound X? A. Ethyl ethanoate. B. Butanoic acid. C. Butyl ethanoate. D. Ethyl butanoate.

1.4 A ball is released from rest from a certain height above the floor and bounces off the floor several times. The position-time graph below represents the motion of the bouncing ball from the instant it was released from rest. Neglecting air resistance, which point (A, B, C or D) on the graph represents the position-time coordinates of the maximum height reached by the ball after the SECOND bounce? A. B. C. D. 1.5 Which ONE of the following pairs of compounds are FUNCTIONAL isomers? A. Methanol and methanal. B. Butane and 2-methylpropane. C. Propan-1-ol and propan-2-ol. D. Propanoic acid and methyl ethanoate. 1.6 Which ONE of the following compounds has the HIGHEST vapour pressure? A. Ethanal. B. Ethane. C. Ethanol. D. Ethanoic acid.

A ball with an unknown mass, m, is thrown horizontally due east towards a wall, and it strikes the wall at a velocity of 36 km·h⁻¹ and rebounds back off the wall at an unknown velocity. Diagrams show the initial momentum (4 kg·m·s⁻¹) and the change in momentum (5,2 kg·m·s⁻¹) of the ball. 5.1 Describe linear momentum. 5.2 Calculate the: 5.2.1 Mass of the ball. 5.2.2 Velocity at which the ball leaves the wall after contact. The letters A to D in the table below represent four organic compounds from different homologous series. Use the table to answer the questions that follow. 6.1 Define homologous series. 6.2 Write down the letter(s) that represent(s) each of the following: 6.2.1 Compound produced during a condensation reaction. 6.2.2 Functional isomer of propanal.

5.5 Compound A undergoes complete combustion according to the following balanced equation: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g). During the combustion, 1,8 kg of carbon dioxide is formed. Calculate the mass of CH₄ needed for this reaction. QUESTION 6: Compounds A, B and C, shown in the table below, are used to investigate a factor which influences the boiling point of organic compounds — A is propanal (CH₃CH₂CHO), B is butanal (CH₃CH₂CH₂CHO), and C is pentanal (CH₃CH₂CH₂CH₂CHO). 6.1 Define the term boiling point. 6.2 For this investigation, write down the: 6.2.1 independent variable; 6.2.2 dependent variable. 6.3 Which ONE of the compounds (A, B or C) has the highest boiling point? 6.4 Explain your answer to Question 6.3, referring to the MOLECULAR STRUCTURE and STRENGTH OF INTERMOLECULAR FORCES between the compounds. 6.5 How will the vapour pressure of 2-methylpropanal compare to that of compound B? Write down only HIGHER THAN, LOWER THAN or EQUAL TO. Explain the answer.

1.4 Which ONE of the following organic compounds will RAPIDLY decolourise bromine water? A. CH₂=CH₂. B. CH₃CH₃. C. CH₃CHO. D. CH₃COOH. 1.5 Which ONE of the following organic compounds has STRUCTURAL ISOMERS? A. Ethanal. B. 1,1-dibromoethane. C. Propane. D. Methanoic acid. QUESTION 2: A satellite of mass 2×10⁴ kg orbits around the surface of planet X at a distance of 4 000 km. Planet X has a mass FOUR TIMES the mass of planet EARTH and a radius which is a THIRD of the radius of the EARTH. 2.1 State Newton's law of Universal gravitation in words. 2.2 Calculate the gravitational force that planet X exerts on the satellite when the satellite is at a distance of 4 000 km from the surface of the planet. 2.3 How does the mass of the satellite on the surface of planet X compare to the mass of the satellite on the surface of planet EARTH? Write down GREATER THAN, LESS THAN OR EQUAL TO.

QUESTION 1: MULTIPLE-CHOICE QUESTIONS. Various options are provided as possible answers to the following questions. Each question has only ONE correct answer; choose the answer and write only the letter (A–D). 1.1 Which of the following represents a SATURATED hydrocarbon? (Four molecular-formula/structural options are given.) 1.2 Which of the following pairs of reactants can be used to prepare the ester called ethyl propanoate in the laboratory? A. Ethane and propanoic acid. B. Propanol and ethanoic acid. C. Ethanol and propanoic acid. D. Ethene and propanol. 1.3 Consider the reaction represented by the equation below: CH₃CH=CH₂ + HBr → CH₃CHBrCH₃. What type of reaction is represented above? A. Halogenation. B. Substitution. C. Hydrogenation. D. Hydrohalogenation. 1.4 Consider the branched chloroalkane structure shown below. The IUPAC name of this compound is: (four naming options are given; one reads: 4-chloro-2,2-dimethylpentane).

1.3 Consider the equation for the reaction below. R is the MAJOR PRODUCT. CH₃CH₂CH=C(CH₃)CH₃ + HBr → R. Which ONE of the following is the CORRECT combination for the type of reaction and the formula of R? A. Addition, CH₃CH₂CHBrCH(CH₃)CH₃. B. Substitution, CH₃CH₂CH₂CBr(CH₃)CH₃. C. Addition, CH₃CH₂CH₂CBr(CH₃)CH₃. D. Substitution, CH₃CH₂CHBrCH(CH₃)CH₃. 1.4 The Maxwell-Boltzmann distribution curve for a sample of a gas in a container is shown below. Which ONE of the following will change the area under the curve? A. The addition of a catalyst. B. A decrease in temperature. C. Gas particles escaping from the container. D. A decrease in concentration by increasing the volume of the container.

2.6 Consider compound C. 2.6.1 To which homologous series does compound C belong? 2.6.2 Give the NAME of the catalyst required in the preparation of compound C. 2.6.3 Draw the STRUCTURAL FORMULA of compound C. QUESTION 3: The factors that affect the vapour pressure of different organic compounds are investigated. The table below shows the vapour pressure, at 25 °C, of five organic compounds represented by the letters A to E: A (propane, molecular mass 44 g·mol⁻¹), B (butane, molecular mass 58 g·mol⁻¹), C (ethyl methanoate), D, and E (propanoic acid, molecular mass 74 g·mol⁻¹). 3.1 Define the term vapour pressure. 3.2 Write down the homologous series to which compounds A and B belong. 3.3 Explain the decrease in vapour pressure from compound A to compound B, as indicated in the table. 3.4 Compounds C and E are functional isomers. 3.4.1 Define molecular formula. 3.4.2 Which compound will have a higher boiling point? 3.4.3 Explain the answer to Question 3.4.2. 3.5 The percentage composition of some of the elements in compound D is given as 61% carbon and 11,86% hydrogen. Determine, with calculations, the empirical formula of compound D. 3.6 Write a balanced equation using molecular formulae for a complete combustion of compound A.