ACJC H2 CHEM P3 Prelim

2 Answer any four questions. (ii) ergie given alculate the enthalpy change for the above reaction. [2] Bond Energies /kJ mol-1 1 Penicillin can be made in the laboratory by reacting 6-aminopenicilanic acid with a suitable acyl chloride. For a particular penicillin, the acyl chloride is the CH3CH2CH=CHCH2COCl. Since the acyl chloride used can be easily made from the corresponding carboxylic acid, the chemist has decided to work with CH3CH2CH=CHCH2CO2H because the acyl chloride is more reactive. (a) (i) The acyl chloride, CH 3CH2CH=CHCH2COCl, can be obtained by reacting CH3CH2CH=CHCH2CO2H with PCl5. Write a balanced equation for the reaction. [1] Using relevant data from the Data Booklet and the bond en s below, c P-Cl P=O 423 322 The carboxylic acid, CH(b) (i) e reaction. [1] (ii) romine. Name and describe the mechanism involved. [4] (iii) in wh ch the hydroxyacid obtained istinguished from its starting material. [2] (c) (i) r w etected. Draw the structure of this ester. Circle the chiral centre(s). [2] (ii) tate the number of sp 2 and sp3 hybridised carbons in the ester. [2] (iii) e re gent nd condition onversion and draw the structure of this diol. [2] (d) (i) including state symb ls for the com f the diol under standard condition. [1] (ii) eriment to etermine the mass of diol used. The following results were obtained. 0 g emperature rise = 44 oC sults give above calcu nthalpy change for the combustion of the diol. [3] [Total: 20] 3CH2CH=CHCH2COOH, can be converted into the hydroxyacid, CH3CH2CH(OH)CH2CH2COOH. Give the reagent and condition for th The hydroxyacid obtained can be distinguished from its starting material by using b Suggest another reagent and condition i can be d In the course of preparing the hydroxyacid, an internal chiral este as also d S This ester may be made into a diol. Give th a a for the c An experiment was carried out to determine the enthalpy change of combustion of this diol. Write a balanced equation o bustion o A large beaker of water was placed on the stove and heated. The temperature rise was recorded. The cylinder was weighed before and after the exp d Mass of diol used = 3.4 g Mass of water heated = 50 T Using relevant data from the Data Book let and r e n , late the e © ACJC 2009 9746/03/Prelim/09 [Turn over

3 [2] (b) tionalize the relative stability of CsI and LiI . [3] (c) (i) values from the Data Booklet, calculate the enthalpy [2] Ca(s) + Ca2+(g)  2Ca+(g) (ii) u onclud about the relative stability of Ca +(g th r spect nd Ca2+? [1] (d) tions between the aqueous ions of Ca and the solid Ca metal is iven as follows: Ca(s) + Ca2+(aq)  2Ca+(aq) ΔH = +63 kJ mol-1 the light of your answer to (c)(ii), account for the differences (if any) noted. [2] (e) (i) t the enthalpy changes associated with the reactions vary considerably. [ 1 ] 2 (a) The triodide ion, I3 -, is known to exist as a stable species in aqueous solution. Draw a dot and cross diagram for I3 - and hence deduce its shape. Solid CsI3 is stable with respect to CsI and I 2 but LiI 3 is not stable with respect to LiI and I 2. Based on your knowledge of the relative stabilities of group II carbonates, ra 3 3 Given that the enthalpy of atomization of Ca is +176.4 kJ mol -1, and using relevant ionization energy change for the reaction: What can yo c e ) wi e to Ca a The energetic rela g In Based on data, the standard electrode potentials of Ca, Sr and Ba are nearly the same, bu . Although there is found to be a good correlation between the ΔH for M 2+(aq) + 2e → M(s) and the corresponding E θ (M2+/M), the degree of similarity between the E θ (M2+/M) is greater whilst that for the Δ H is noticeably lower. What factor is responsible for the dissimilarity of the set ΔH values? Mg Ca Sr Ba Eθ (M2+ / M) / V -2.38 -2.87 -2.89 -2.90 ΔH / kJ mol-1 M2+(aq) + 2e → M(s) -403.2 -256.2 -289.8 -365.4 (ii) a l u e s f o r M g . [2] (iii) (ii), what energy term will give a ore exact correlation with the Eθ? Why? [2] (f) . What other factor is relevant in ex laining eakness of HF(aq) as an acid? [1] (g) (i) uggest what phenomenon is responsible for this deviation. [2] For Mg, ΔH deviates so greatly, that no good correlatio n can be observed between ΔH and Eθ. Suggest a reason for this inconsistency between the two v In the light of your answers to (e)(i) and (e) m HF(aq) is the weakest acid compared with the other aqueous hydrogen halides. One factor relevant to its weakness is that the entropy change that accompanies its dissociation is the most negative p the w The enthalpy of vaporisation of the hydrogen halides is markedly different for one of the HX as compared with the others. Identify the hydrogen halide and s © ACJC 2009 9746/03/Prelim/09 [Turn over

4 © ACJC 2009 9746/03/Prelim/09 [Turn over

5 f evaporation ( ΔHvap) divided by the boiling point (T b/ K) is approximately constant for HC l, HBr and HI, but very different for HF. How would you expect (ii) The values of entropies of vaporization ( ΔSb), that is the molar latent enthalpy o the entropie s of vaporization for HF to compare with the other three? Why? [2] [Total: 20] © ACJC 2009 9746/03/Prelim/09 [Turn over

6 p (a) P cl [7] (b) W in [2] 3 Glycine, H 2NCH2COOH, is the smallest of the 20 amino acids commonly found in roteins. ropose a synthesis pathway to obtain glycine starting from chloromethane. State early all int ermediates, reagents and conditions. ould you expect the amine group in glycine to have a bigger or smaller K b than that proline? Explain your answer briefly. N COOH H proline has many uses. For example a u in cids, (c) Glycine it can serve s a b ffering agent anta analgesics, antiperspirants, cosmetics, and toiletries. With the use of equations, show h yc (d) In a rea The res placed plate. ow gl ine can acts as a buffer. [2] ction, tripeptide S produces the following amino acids in equimolar amounts. ulting solution was added to an excess of a buffer solution of pH 4.0 and at the centre of the plate. A potential difference was then applied across the Amino Acid H2NC H C CH2 OH O CH2 CH2 CH2 H2NC H C NH2 Lys OH O H Gly H2NC H C CH2 OH O CH2 C OH O Glu pI 9.7 6.0 3.2 (i) Draw a possible structure of tripeptide S. [1] (ii) What reagent and condition are needed break tripeptide S into its constituent amino acids? What is the name given to this type of reaction? [2] (iii) Draw the predominant form of the three amino acids in the buffer solution and hence explain how they can be separated. [6] [Total: 20] © ACJC 2009 9746/03/Prelim/09 [Turn over

7 © ACJC 2009 9746/03/Prelim/09 [Turn over

8 (a) wate heate his raises th electr ity co sump shortens the lifespan of the appliances. Hard water is treated through a softening process, where the metal ions are removed, before it is used for consumption. A sample of hard water containing Mg 2+ (aq) was collected. The presence of Mg 2+ is to be tested by precipitating MgCO3. (i) Write an expression for the solubility, K sp, of magnesium hydroxide. [1] (ii) The solubility of Mg(OH) 2 in pure water at 25 oC is