2009 JC1 H1 chem Promo QP

1 2009Section A 1 (a) [5] (b) (i) (ii) [5] (c) (i) [5] (ii) (d) [2] (e) (i) (ii) [3] [20 marks] Answer the following question on writing paper. One of the most common uses of alkanes is to burn them in air in the internal combustion engine. Alkanes containing between 8 and 12 carbon atoms per molecule are preferred for this. Draw possible structural formulae for the hydrocarbon with lecular formula C8H18. Include in your answers the structure with the highest boiling point, and the structure with the lowest boiling point. Give reasons for your choice of structures. Write a balanced equation for the complete combustion octane, C8H18, and hence calculate the volume of air (at room temperature and pressure) needed to burn 57g octane. [Assume air contains 20% oxygen by vo ume.] In a separate experiment, a mixture of octane and brom was exposed to UV light. State and explain what you would observe. Ethane, C2H6, is another member of the alkane series. Explain how the boiling points of the following compounds will compare with that of ethane. chloroethane, C2H5Cl any isomer of C8H18. Ethanol, C2H5OH, is a colourless water-soluble alcohol. Draw a diagram to illustrate clearly the interaction between C2H5OH and H2O molecules. The ethene molecule, C2H4, is said to be planar. The two carbon atoms of ethene can be described as bei g joined by a and a . Briefly explain the terms in , using diagrams where appropriate. Give the numbers of and bonds present in the ethene molecule. three s p -bond -bond italics σ π

2 Section B all 2 (a) (i) (ii) (iii) [6] (b) Answer the questions in this section in the spaces provided. Beryllium chloride, BeCl2, is a molecular solid with a melting point of 399oC. When the solid is vapourised, the vapour is found to consist of a mix of gaseous molecules of BeCl2 and Be2Cl4. Draw a dot-and-cross diagram to show the electronic structure of a molecule of BeCl2. Suggest how you would expect Be2Cl4 to form from BeCl2. Draw a diagram to show the types of bonds present in the Be2Cl4 molecule. Give a value for each of the Cl-Be-Cl and Be-Cl-Be bond angles. Cl-Be-Cl = Be-Cl-Be = Ions of BeCl2 and Be2Cl4 can be obtained by passing the vapour through a plasma torch. The following equations show some of the ions formed. BeCl2 BeCl2 + + e Be2Cl4 Be2Cl4 + + e ∠ ∠ à à

3 3o Figure 1 below shows the pathway of Be2Cl4 + in an electric field. Suggest why energy is required to convert the Be2Cl4 molecule to its corresponding Be2Cl4 + ion. Indicate the polarity (+ or -) of both plates in Figure 1. In Figure1, draw and label the pathway of the BeCl2 + ion. Explain the position of this pathway. Explain the terms , and . Be2Cl4 + source Figure 1 (i) (ii) (iii) [4] [10 marks] 3 (a) [3] rate equation order of reaction rate constant

4 I II (b) Experiment number Initial conc of ester / mol dm–