11.5. Alkenes
A subsection of Chemistry, 0620, through 11. Organic chemistry
Listing 10 of 149 questions
Methanol can be made from a mixture of carbon monoxide and hydrogen. CO+ 2H2CH3OHThe forward reaction is exothermic. Explain why the concentration of methanol at equilibrium does not change. Suggest conditions, in terms of temperature and pressure, which would give a high yield of methanol. How would the conditions used in practice compare with those given in ? Give an explanation of any differences. Biodiesel is made from a vegetable oil by the following reaction. + + 3CH3OH → 3C17H35COOCH3 CH2OH CHOH CH2OH C17H35 CO2 CH2 C17H35 CO2 CH C17H35 CO2 CH2 vegetable oil methanol biodiesel glycerol What type of compound are vegetable oil and biodiesel? What other useful product is made from vegetable oil by heating it with aqueous sodium hydroxide? Suggest an explanation why making and using biodiesel has a smaller effect on the percentage of carbon dioxide in the atmosphere than using petroleum-based diesel. Petroleum-based diesel is a mixture of hydrocarbons, such as octane and octene. ‘Oct’ means eight carbon atoms per molecule. Draw a structural formula of an octene molecule. Describe a test which would distinguish between octane and octene. test result with octane result with octene
0620_s11_qp_32
THEORY
2011
Paper 3, Variant 2
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Methanol can be made from a mixture of carbon monoxide and hydrogen. CO+ 2H2CH3OHThe forward reaction is exothermic. Explain why the concentration of methanol at equilibrium does not change. Suggest conditions, in terms of temperature and pressure, which would give a high yield of methanol. How would the conditions used in practice compare with those given in ? Give an explanation of any differences. Biodiesel is made from a vegetable oil by the following reaction. + + 3CH3OH → 3C17H35COOCH3 CH2OH CHOH CH2OH C17H35 CO2 CH2 C17H35 CO2 CH C17H35 CO2 CH2 vegetable oil methanol biodiesel glycerol What type of compound are vegetable oil and biodiesel? What other useful product is made from vegetable oil by heating it with aqueous sodium hydroxide? Suggest an explanation why making and using biodiesel has a smaller effect on the percentage of carbon dioxide in the atmosphere than using petroleum-based diesel. Petroleum-based diesel is a mixture of hydrocarbons, such as octane and octene. ‘Oct’ means eight carbon atoms per molecule. Draw a structural formula of an octene molecule. Describe a test which would distinguish between octane and octene. test result with octane result with octene
0620_s11_qp_33
THEORY
2011
Paper 3, Variant 3
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The alkenes are unsaturated hydrocarbons. They form a homologous series, the members of which have similar chemical properties: ● easily oxidised ● addition reactions ● polymerisation ● combustion. All the alkenes have the same empirical formula. State their empirical formula. Why is the empirical formula the same for all alkenes? Alkenes can be oxidised to carboxylic acids by boiling with aqueous potassium manganate(. Pent-2-ene, CH3–CH2–CH=CH–CH3, oxidises to CH3–CH2–COOH and CH3COOH. Name these two acids. CH3–CH2–COOH CH3COOH Most alkenes oxidise to two carboxylic acids. Deduce the formula of an alkene which forms only one carboxylic acid. Complete the following equations for the addition reactions of propene. CH3–CH=CH2 + Br2 → CH3–CH=CH2 + H2O → Draw the structural formula of poly 0.01 moles of an alkene needed 2.4 g of oxygen for complete combustion. 2.2 g of carbon dioxide were formed. Determine the following mole ratio. moles of alkene : moles of O2 : moles of CO2 From this ratio determine the formula of the alkene. Write an equation for the complete combustion of this alkene.
0620_s12_qp_32
THEORY
2012
Paper 3, Variant 2
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The alkenes are unsaturated hydrocarbons. They form a homologous series, the members of which have similar chemical properties: ● easily oxidised ● addition reactions ● polymerisation ● combustion. All the alkenes have the same empirical formula. State their empirical formula. Why is the empirical formula the same for all alkenes? Alkenes can be oxidised to carboxylic acids by boiling with aqueous potassium manganate(. Pent-2-ene, CH3–CH2–CH=CH–CH3, oxidises to CH3–CH2–COOH and CH3COOH. Name these two acids. CH3–CH2–COOH CH3COOH Most alkenes oxidise to two carboxylic acids. Deduce the formula of an alkene which forms only one carboxylic acid. Complete the following equations for the addition reactions of propene. CH3–CH=CH2 + Br2 → CH3–CH=CH2 + H2O → Draw the structural formula of poly 0.01 moles of an alkene needed 2.4 g of oxygen for complete combustion. 2.2 g of carbon dioxide were formed. Determine the following mole ratio. moles of alkene : moles of O2 : moles of CO2 From this ratio determine the formula of the alkene. Write an equation for the complete combustion of this alkene.
0620_s12_qp_33
THEORY
2012
Paper 3, Variant 3
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Match the name of the homologous series on the left with its formula on the right. The fi rst one has been done for you. halogenoalkane alkane alkene alcohol carboxylic acid C2H6 C2H4 C2H5OH C2H5Cl CH3COOH Draw the full structural formula of the compound, C2H6, showing all atoms and bonds. The compound with the formula C2H4 is an unsaturated hydrocarbon. Describe the difference between a saturated and an unsaturated hydrocarbon in terms of the bonds they contain. Describe a test to distinguish between a saturated and unsaturated hydrocarbon. test result with saturated hydrocarbon result with unsaturated hydrocarbon
0620_s13_qp_21
THEORY
2013
Paper 2, Variant 1
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A teacher placed a few drops of liquid bromine in the bottom of a test-tube containing a solvent. After 10 minutes, the brown colour of the bromine had spread a little way through the solvent. After 2 hours, the brown colour had spread throughout the solvent. at the start after 10 minutes after 2 hours solvent liquid bromine Use the kinetic particle theory to explain these observations. Bromine is a halogen in Group VII. The properties of some halogens are given in the table below. halogen melting point / °C boiling point / °C density at boiling point in g / cm3 electron arrangement of halogen atom fluorine –220 –188 1.51 2,7 chlorine –101 –35 1.56 2,8,7 bromine –7 +59 2,8,18,7 iodine +114 +184 4.93 2,8,18,18,7 Use the information in the table to: Deduce the state of fluorine at –200 °C. Describe how the melting point changes down Group VII. Estimate the density of bromine. Deduce the number of completely filled electron shells in an atom of chlorine. Aqueous bromine reacts with aqueous potassium iodide to form iodine and potassium bromide. Complete the equation for this reaction. Br2 + 2KI + 2KBr Explain why aqueous bromine does not react with an aqueous solution of potassium chloride. Bromine reacts with fluorine to form bromine trifluoride, BrF3. Calculate the relative molecular mass of bromine trifluoride. Show all your working.
0620_s15_qp_22
THEORY
2015
Paper 2, Variant 2
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Hydrocarbons are compounds which contain hydrogen and carbon only. • 10 cm3 of a gaseous hydrocarbon, CxHy, are burned in 100 cm3 of oxygen, which is an excess of oxygen. • After cooling to room temperature and pressure, there is 25 cm3 of unreacted oxygen, 50 cm3 of carbon dioxide and some liquid water. All volumes are measured under the same conditions of temperature and pressure. What is meant by an excess of oxygen? What was the volume of oxygen that reacted with the hydrocarbon? Complete the table below to express the smallest whole number ratio of volume of hydrocarbon reacted : volume of oxygen reacted : volume of carbon dioxide produced volume of hydrocarbon reacted volume of oxygen reacted volume of carbon dioxide produced smallest whole number ratio of volumes Use your answer to to find the mole ratio in the equation below. Complete the equation and deduce the formula of the hydrocarbon. CxHy+ O2→ CO2+ H2Oformula of hydrocarbon = Cracking is used to convert long chain alkanes into shorter chain alkanes and alkenes. Alkenes are unsaturated compounds. Decane, C10H22, can be cracked to give propene and one other product. Complete the chemical equation. C10H22 → C3H6 + What is meant by the term unsaturated? Describe a test to show that propene is an unsaturated compound. test result Propene can be polymerised. The only product is polypropene. The equation for the polymerisation is: n C H CH3 C H H nC3H6 Name the type of polymerisation that occurs. Deduce the maximum mass of polypropene that could be produced from 1 kg of propene. kg Give the empirical formula of propene, polypropene.
0620_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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Questions Discovered
149