Organic Chemis

Topics: Sodium, Sodium hydroxide, Standard enthalpy change of formation Pages: 13 (2670 words) Published: November 13, 2012
M09/4/CHEMI/HP2/ENG/TZ1/XX+

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CHEMISTRY HIGHER lEvEl PaPER 2 Monday 18 May 2009 (afternoon) 2 hours 15 minutes INSTRUCTIONS TO CANDIDATES Write your session number in the boxes above. Do not open this examination paper until instructed to do so. Section A: answer all of Section A in the spaces provided. Section B: answer two questions from Section B. Write your answers on answer sheets. Write your session number on each answer sheet, and attach them to this examination paper and your cover sheet using the tag provided. • At the end of the examination, indicate the numbers of the questions answered in the candidate box on your cover sheet and indicate the number of sheets used in the appropriate box on your cover sheet. •

Candidate session number 0 0

2209-6108

19 pages © International Baccalaureate Organization 2009

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2– Section a Answer all the questions in the spaces provided. 1.

M09/4/CHEMI/HP2/ENG/TZ1/XX+

Biodiesel makes use of plants’ ability to fix atmospheric carbon by photosynthesis. Many companies and individuals are now using biodiesel as a fuel in order to reduce their carbon footprint. Biodiesel can be synthesized from vegetable oil according to the followingreaction. O H C O C R O H C O C R (l)+ 3CH3OH(l) O H C O C R H H

H

NaOH(s)

H C OH H C OH (l)+3 CH3 H C OH H

O O C R (l)

vegetableoil (a)

methanol

glycerol

biodiesel [1]

Identifytheorganicfunctionalgrouppresentinbothvegetableoilandbiodiesel. .......................................................................

(b) For part of her extended essay investigation into the efficiency of the process, a student reacted a pure sample of a vegetable oil (where R=C17H33) with methanol. Therawdatarecordedforthereactionisbelow. Massofoil = 1013.0g Massofmethanol = 200.0g Massofsodiumhydroxide = 3.5g Massofbiodieselproduced= 811.0g Therelativemolecularmassoftheoilusedbythestudentis885.6.Calculatetheamount (inmoles)oftheoilandthemethanolused,andhencetheamount(inmoles)ofexcess [3] methanol.

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(This question continues on the following page)

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3– (Question 1 continued) (c)

M09/4/CHEMI/HP2/ENG/TZ1/XX+

The reversible arrows in the equation indicate that the production of biodiesel is an equilibriumprocess. (i) Statewhatismeantbythetermdynamic equilibrium. .................................................................. .................................................................. (ii) Using the abbreviations [vegetable oil], [methanol], [glycerol] and [biodiesel] deducetheequilibriumconstantexpression(Kc)forthisreaction. [1] [1]

(iii) Suggestareasonwhyexcessmethanolisusedinthisprocess. .................................................................. .................................................................. (iv) Stateandexplaintheeffectthattheadditionofthesodiumhydroxidecatalystwill haveonthepositionofequilibrium. [2] .................................................................. .................................................................. .................................................................. (d) Thereactantshadtobestirredvigorouslybecausetheyformedtwodistinctlayersinthe reactionvessel.Explainwhytheyformtwodistinctlayersandwhy...
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