MI 2009 H1 CHEM P2 Promos

Class Adm No Candidate Name: This question paper consists of 15 printed pages. Promotional Examination II 2009 Pre-university 2 H1 CHEMISTRY 8872 PAPER 2 8872 / 2 Wednesday 23 September 2009 2 h Additional materials: Answer booklet Cover page Data Booklet 5 pieces of writing paper READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name, index number and class on all the work you hand in. Write in dark blue or black pen on both sides of the writing paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluids. Section A Answer all questions. Section B Answer any two questions on the writing papers. Start each new question on a fresh sheet of writing paper. At the end of the examination, hand in your answers to Section A and Section B separately. Attach the cover page to your answer scripts for Section B. The number of marks is given in brackets [ ] at the end of each question or part question. FOR EXAMINER’S USE A B (2 questions) Total Section Q1 Q2 Q3 Q4 Q1 Q2 Q3 Marks 10 10 10 10 20 20 20 80 [Turn over

2 ( Section A Answ er ALL questions in the spaces provided. 1. (a) What do you understand by the term order of reaction? [1] .......................................................................................................................................... .......................................................................................................................................... (b) Cyanohydrins can be converted easily to useful organic acids. To form cyanohydrins, ketones are reacted with a basic solution of sodium cyanide. CH3CH2)2C=O + HCN  (CH3CH2)2C(OH)CN pentanone The above reaction was carried out with different concentrations of the three reagents and the following results were obtained and recorded in the table below. Experiment number [(CH3CH2)2C=O] / mol dm-3 [H+] / mol dm-3 [CN-] / mol dm-3 Relative initial rate 1 0.0400 0.0600 0.0600 2.000 2 0.0400 0.0400 0.0500 1.666 3 0.0500 0.0800 0.0500 2.084 A chemist determined that the order of reaction is zero with respect to hydrogen ions. Deduce the order of reaction with respect to pentanone and cyanide ions. Hence write a rate equation for the reaction. [3]

3 (c) (CH 3CH2)2C(OH)CN can be synthesized from Alcohol G by the following series of reactions. I II (CH 3CH2)2C=O (CH 3CH2)2C(OH)CN Alcohol G HCN + trace of NaOH(aq) III (CH3CH2)2C(OH)CO2H (i) State the name of Alcohol G. [1] ...................................................................................................................................... (ii) Suggest reagents and conditions for reactions I and III. [2] Reaction I: ................................................................................................................ Reaction III: ............................................................................................................... (iii) (CH 3CH2)2C(OH)CO2H produced in the above reaction is soluble in water. With the aid of suitable diagrams, explain how this is so. [2] .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... (iv) State the structural formula of the organic compound formed when Alcohol G is refluxed with propanoic acid in the presence of concentrated sulphuric acid. [1] .......................................................................................................................................... [Turn over

4 2. (a) A key reaction in production of acid rain is the formation of nitrogen dioxide gas. This gas is produced from the reaction between nitrogen monoxide and oxygen. O2(g) + 2NO(g)  2NO2(g) (i) Given the following data, calculate the enthalpy change for the above reaction. Show your workings clearly. [1] Substance ∆Hf / kJ mol-1 NO(g) + 90.3 NO2(g) + 33.2 (ii) Sketch a clearly labelled energy profile diagram in the space below for the above reaction, assuming it is a one-step reaction. Include the enthalpy change value calculated in (i) on the diagram. [2]

5 (b) Oxides of sulphur are also responsible for the formation of acid rain. In the laboratory, at room temperature, the presence of sul phur dioxide gas can be confirmed with an acidified solution of potassium dichromate(VI). The equation for this reaction is shown below. 3SO2 (g) + Cr2O7 2- (aq) + 2H+ (aq) → 3SO4 2- (aq) + 2Cr3+ (aq) + H2O (l) (i) State the oxidation number of sulphur in SO 2 and SO 4 2- in the equation above. [1] O.N. of S in SO2 : .................. O.N. of S in SO 4 2- : .................. (ii) e 0 20 m l dm -3 alcu volume of sulphur dioxide used in t he reaction. [2] (iii) with water. Suggest an approximate pH for the resulting solution. [2] (iv) reference to their intermolecular forces of attraction, explain this difference. [2] .......................................................................................................................................... A sample of sulphur dioxide reacts exactly with 50.0 cm3 dichromate(VI) solution. The resulting chromium(III) solution is found to b .1 o . C late the Describe, with the aid of a balanced equation, the reaction of sulphur dioxide .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... The boiling points of SO 2 and SO 3 are -10 °C and 45 °C respectively. With .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... [Turn over

6 3. (a) In the synthesis of various types of organic compounds, 2-chlorobutane is a useful reagent. One of the reactions that 2-chlorobutane can undergo is elimination reaction to form but-2-ene (Mr = 56.0) which exhibits cis-trans isomerism. (i) Draw the structural formula of the cis and trans isomers of but-2-ene in the space provided below.