14. Hydrocarbons
A section of Chemistry, 9701
Listing 10 of 313 questions
The gas ethyne, C2H2, more commonly known as acetylene, is manufactured for use in the synthesis of organic compounds. It is also used, in combination with oxygen, in ‘oxy-acetylene’ torches for the cutting and welding of metals. Industrially, ethyne is made from calcium carbide, CaC2, or by cracking liquid hydrocarbons. When calcium carbide is reacted with water, ethyne and calcium hydroxide are formed. Construct a balanced equation for this reaction. Ethyne can also be obtained from ethene by using the following sequence of reactions. CH2CH2 HCCH ClCH2CH2Cl step 1 step 2 What types of reaction are step 1 and step 2? step 1 step 2 Suggest what reagent and conditions would be used in a laboratory in step 2. reagent conditions When ethyne is passed into water at 60 °C, in the presence of a little H2SO4 and Hg2+ ions, a pungent, colourless organic liquid, Q, with Mr of 44 is obtained. This is step 3. When Q is warmed with Tollens’ reagent in a test-tube, a silver mirror is formed. On acidification, the solution remaining in the test-tube is found to contain the organic compound R which has Mr of 60. This is step 4. Give the structural formulae of Q and R. HCCH step 3 Q step 4 R What type of reaction is step 3 and step 4? step 3 step 4 The standard enthalpy change of combustion of C2H2, ΔH o–– c, is –1300 kJ mol–1 at 298 K. Values of relevant standard enthalpy changes of formation, ΔH o–– f, measured at 298 K, are given in the table. substance ΔH o–– f / kJ mol–1 CO2–394 H2O–286 Write balanced equations, with state symbols, that represent the standard enthalpy change of combustion, ΔH o–– c, of C2H2, and the standard enthalpy change of formation, ΔH o–– f, of C2H2. Use the data above and your answer to to calculate the standard enthalpy change of formation, ΔH o–– f, of C2H2. Show clearly whether the standard enthalpy change of formation of C2H2 has a positive or negative value.
9701_s11_qp_21
THEORY
2011
Paper 2, Variant 1
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Questions Discovered
313