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14. Hydrocarbons
A section of Chemistry, 9701
Listing 10 of 313 questions
V is a colourless liquid. V HO O V reacts with an excess of LiAl H4 to form W. Draw the structure of W in the box. W Identify the role of LiAl H4 in the reaction with V. V reacts to form Z in a single reaction, as shown in . V HO O Z HO O OH OH Suggest the reagent and conditions needed to form Z from V. Deduce the empirical formula of Z. Complete Table 4.1 to show the number of sp2 and sp3 hybridised carbon atoms that are present in a molecule of V. Table 4.1 type of hybridisation sp2 sp3 number of carbon atoms in V Q contains the elements carbon, hydrogen and oxygen only. It is a saturated molecule with no branching in its carbon backbone. Q contains only one functional group. The relative molecular mass of Q is 88. No effervescence is seen when Na2CO3 is added to Q. Effervescence is seen when sodium is added to Q. Q reacts with alkaline I2to form a yellow precipitate. Draw the structure of Q in the box. Q
9701_s23_qp_21
THEORY
2023
Paper 2, Variant 1
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In industry, ethanol is made by reacting ethene with steam in the presence of H3PO4. reaction 1 C2H4+ H2OC2H5OHUse the bond energy values in Table 4.1 to calculate the enthalpy change, ΔHr , for reaction 1. Table 4.1 bond bond energy / kJ mol–1 C–C C=C C≡C C–H C–O C=O O–H ΔHr = kJ mol–1 Reaction 1 reaches equilibrium at constant temperature and pressure. Deduce what effect increasing the pressure will have on the amount of ethanol in the new equilibrium mixture. Use Le Chatelier’s principle to explain your answer. effect of increasing pressure explanation The mechanism for reaction 1 can be described in three steps. Steps 1 and 2 for reaction 1 are shown in . step 1 step 2 H2C H HO OH O CH2 H H2C H P O HO OH O– P O C+ H H2C H H H H C+ H H3C CH2 O+ H H O Describe the behaviour of H3PO4 in step 1 in . Explain your answer. Identify the species that behaves as an electrophile in step 2 in . Explain your answer. Complete to show the mechanism for step 3 of reaction 1. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. H HO OH O P O HO OH O– P O H3C CH2 O+ H H3C CH2 O H H Describe how a catalyst affects a reaction. Explain your answer. Use and to justify why H3PO4 is described as a catalyst in reaction 1. Propene also reacts with steam. A mixture of organic products is produced. Explain why propan-2-ol is produced in the higher yield. Describe the covalent bonds present between the carbon atoms in an ethene molecule by completing Table 4.2. Table 4.2 sigma (σ ) pi (π) type of orbitals involved in bond how the orbitals overlap
9701_s23_qp_22
THEORY
2023
Paper 2, Variant 2
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Y is formed from X in a single-step reaction, as shown in . X Y O O HO OH OH Deduce the empirical formula of Y. The formation of Y from X requires the addition of a suitable reducing agent. Construct an equation using molecular formulae and for the reaction in . Use to represent one atom of hydrogen from the reducing agent. Identify a suitable non-gaseous reducing agent for the formation of Y from X. Complete Table 5.1 to show the number of sp2 and sp3 hybridised carbon atoms in a molecule of X. Table 5.1 type of hybridisation sp2 sp3 number of carbon atoms in X Complete Table 5.2 with the expected observations that occur when the reagents shown are added to separate solutions of X and Y. Do not refer to temperature changes in your answer. Table 5.2 reagent observation on addition to X observation on addition to Y aqueous sodium carbonate 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) alkaline aqueous iodine
9701_s23_qp_23
THEORY
2023
Paper 2, Variant 3
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Questions Discovered
313