RVHS Prelim P3 QP

1 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9729/03 Paper 3 Free Response 18 September 2018 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer one question. Begin each question on a fresh sheet of paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything on it. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the exami nation, fasten all your work secu rely together, wit h the cover page on top. This document consists of 15 printed pages and 1 blank page.

2 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations Section A Answer all the questions in this section. 1 (a) (i) Phosphorus reacts with • F 2 to produce PF5 as the only product. • C l2 to give both PCl5 and PCl3. • Br 2 and I2 to give PBr3 and PI3 respectively. With reference to the Data Booklet, explain the difference in oxidation states of phosphorus in the phosphorus-containing compounds formed. [3] (ii) The table below gives the pKa values of the hydrogen halides. hydrogen halide p Ka HF 3.17 HCl –7 HBr –9 HI –10 Explain the trend in the pKa values. [2] (b) The following reaction scheme shows the formation of an alcohol via the Grignard reaction. RM g B r R' R" O O R' R" R MgBr dilute acid OH R' R" R + MgBr(OH) Step I Step II (i) Suggest the type of reaction undergone in Step II. [1] (ii) Suggest the identities of a suitable carbonyl compound and Grignard reagent to form 1-methylcyclohexan-1-ol. [2] (iii) The reaction between the car bonyl compound and the Grignard reagent suggested in (b)(ii) is a nucleophilic addition. Propose the mechanism for this reaction, assuming that the Grignard reagent (R-MgBr) produces the , as the reacting species to form 1-methylcyclohexan-1-ol. [3] Grignard reagent

3 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations (c) Calcium phosphate, Ca3(PO4)2, is a sparingly soluble salt. .. (i) Write the expression for the solubility product of calcium phosphate. [1] (ii) Given that the solubility of calcium phosphate in water is 1.14 × 10 –7 mol dm –3, calculate the solubility product of calcium phosphate, stating its units. [2] (iii) Calculate the solubility of calc ium phosphate in the presence of 0.150 mol dm–3 of potassium phosphate. [2] (iv) A saturated solution was prepar ed by dissolving two sparingly soluble salts, calcium phosphate and calcium sulfate, CaSO 4, in tap water. The tap water used wa s found to be contaminated with trace amounts of SO42–. Explain the impact of the contam ination on the solubilities of calcium phosphate and calcium sulfate. [2] [Total: 18]

4 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations 2 Strepsils® is a line of throat lozenges used to relieve discomfort caused by mouth and throat infections. The table below shows the main active and non-active ingredients found in one lozenge. primary active ingredients 2,4-dichlorobenzyl alcohol amylmetacresol non-active ingredients (–)-menthol tartaric acid propylene glycol

5 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations (a) 2,4-dichlorobenzyl alcohol can be prepared from 2,4-dichlorobenzyl chloride (shown below) via a one-step synthesis. ( i ) State the reagent and condition for the reaction. [1] ( i i ) Explain why the molecule below will not be obtained as a by-product. [1] ( i i i ) A student carries out the synt hesis using the reagent in (a)(i) that has been contaminated with sodium ethoxide. Draw the structure of the possible by-product that may result. [1] ( i v ) Describe a simple chemical test that can distinguish between 2,4-dichlorobenzyl alcohol and amylmetacresol. State the expected observations for each compound. [2] (b) Arrange amylmetacresol, menthol and tartar ic acid in increasing order of acidity. Explain your answer. You only need to consider the first acid dissociation of tartaric acid. [3]

6 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations (c) Menthol is produced commercially vi a the Haarmann-Reimer process. A modified version of the process is shown below. OH AlCl3, HCl step 1 OH heat at high P step 2 H2 / Pd OH crude methanol step 3 O O step 4OH ( i ) Suggest the types of reactions occurring in steps 1 and 2. [2] ( i i ) Given that crude menthol does not ex hibit optical activity, determine the number of enantiomers crude menthol has. Hence, calculate the proportion of each enantiomer formed. [2] ( i i i ) Draw the structure of the by-product formed. [1] (d) (i) A 25.0 cm3 solution of 0.0100 mol dm–3 tartaric acid in a conical flask is titrated with 0.0100 mol dm–3 NaOH(aq) from a burette. Given that p Ka1 = 2.89 and p Ka2 = 4.40, and ignoring the auto- ionisation of water, determine the pH of the solution when the following volumes of NaOH(aq) are added: • 0.00 cm 3 • 12.50 cm 3 • 50.00 cm 3 [4] ( i i ) When the second equivalenc e point is reached, th e solution is heated to dryness. The residue left is a white solid. Explain, using structure and bonding, why the boiling point of the solid residue is higher than that of tartaric acid. [2] (–)-menthol crude menthol by-product +

7 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations (e) Propylene glycol can be produced from gaseous propene. ( i ) State the reagent and condition required for propene to form propylene glycol. [1] ( i i ) When propene is reacted with the reagent in (e)(i) under a different set of condition, an organic liquid and an inorganic gas are formed. Draw the displayed formula of the organic liquid. [1] ( i i i ) The inorganic gas is collected in an evacuated glass bulb at 30 °C. It is found that the mass of the 500 cm3 glass bulb increased by 0.36 g. Identify the inorganic gas and dete rmine the pressure of the gas collected. [2] [Total:23]

8 River Valley High School 9729/03 [Turn over 2018 Preliminary Examinations 3 Transition elements and their compound s have found many applications in industries as both homogeneous and heterogeneous catalysts. For example, nickel is used as a cata lyst for hydrogenation of alkenes and vanadium pentoxide (V2O5) is used in the manufacture of sulfuric acid. (a) Explain what is meant by the term heterogeneous catalyst. [2] (b) The following table list the colours of various vanadium ions in aqueous solution: ion oxidation state colour V2+ +2 violet V3+ +3 green VO2+ +4 blue VO3− +5 yellow When a sample of yellow VO 3− solution is mixed with an excess of zinc powder, the solution undergo a series of colour changes over time. Using relevant E⦵ values from the Data Booklet, account for all the observed colour changes. There is no need to write any balanced chemical equation. [3] (c) A similar process as (b) was carried out as follows: 100 cm3 of 0.0500 mol dm−3 of NaVO3 is reacted completely with zinc powder. The final colour of the solution is blue-green. 25.0 cm3 of this blue-green solution requires 20.63 cm 3 o