CHEMISTRY 1 SK015 SESSION 2023/2024 SETARA PSPM1 KOLEJ MARA KULIM 4 Answer all questions. 1. (a) Iron is an element with a proton number of 26. It was found that the iron atoms have three different nucleon numbers 56, 57 and 58 respectively. (i) Write the isotopic notation of these three isotopes of iron. (ii) A sample of iron contains 78.6% atoms with a nucleon number 56, 10.1% atoms with a nucleon number 57 and 11.3% atoms with a nucleon number 58. Calculate the relative atomic mass of iron. (iii) Sketch and label the expected mass spectrum of iron. [6 marks] (b) Monosodium glutamate (MSG), a food-flavour enhancer, has the following composition by mass of 35.51% carbon, 4.77% hydrogen, 37.85% oxygen, 8.29% nitrogen and 13.60% sodium. Calculate its molecular formula if the molar mass is 169.0 g mol-1 . [5 marks] (c) A solution with density 1.6 g cm-3 contains 8.0 g of ammonium nitrate, NH4NO3, in 500 mL of solution. Determine, (i) molarity of solution. (ii) the mass of water used to prepare this solution. [5 marks] (d) Ethylene, C2H4, is an important industrial organic chemical and can be prepared by heating hexane, C6H14, at 800oC. C6H14 C2H4 + C3H6 + CH4 If the percentage yield of ethylene, C2H4, is 42.5%, calculate the mass of hexane must be reacted to produce 481.0g of ethylene. [5 marks] 2. (a) An electron in a hydrogen atom falls from n = 5 to n = 3. Calculate the energy of the photon emitted and the wavelength of the spectral line produced. State the series of this line spectrum. [5 marks]
CHEMISTRY 1 SK015 SESSION 2023/2024 SETARA PSPM1 KOLEJ MARA KULIM 5 (b) The orbital diagram below shows electronic configurations that is not allowed. State the principles it is not obeyed. Explain. [2 marks] (c) Copper is the nineth element in the first row of d-block element. Write the electronic configuration of copper according to the Aufbau principle and the actual configuration. Give reason(s) for any anomaly. [3 marks] 3. (a) Figure 1 shows the possible Lewis structures for hydrazoic acid, N3H. I II III Figure 1 (i) Calculate formal charge on each structure I until III. (ii) Determine the most plausible Lewis structure. Explain. [5 marks] (b) Figure 2 below shows glycine, NH2CH2COOH, one of the essential amino acid. (i) Complete the Lewis structure of glycine. (ii) State the geometry of the central atom labelled as x and y. (iii) State the hybrid orbital of all central atoms of N, C and O. (iv) Draw the orbital overlapping of this molecule. [10 marks] (c) Explain why viscosity of a liquid decreases with increasing in temperature. [2 marks] ↑↑ ↑ ↑ ↑ 2s 2p
CHEMISTRY 1 SK015 SESSION 2023/2024 SETARA PSPM1 KOLEJ MARA KULIM 6 4. (a) Hydrogen gas is collected over water when calcium metal reacts with water. The volume of gas collected is 641.0 mL at 30oC and pressure recorded is 988 mmHg. Calculate the mass of the hydrogen gas collected. (Pressure of water vapour at 30oC is 31.82 mmHg) [3 marks] (b) The triple point temperature and pressure of CO2 is -56.6oC and 5.11 atm. While the critical point is at 31.0oC and 72.9 atm. (i) Sketch and label the phase diagram of CO2. (ii) Explain the change in the melting point of CO2 when pressure is increased. (iii) State the phase changes when the pressure is increases from 1.0 atm to 38.0 atm isothermally at 0oC. [6 marks] 5. Sulfuryl chloride, SO2Cl2, gas dissociates reversibly into sulphur dioxide gas, SO2 and chlorine gas, Cl2. The reaction is endothermic. (a) Suggest two possible ways to increase the chlorine production. Explain your answer. (b) An amount of 0.20 mol of SO2Cl2 was placed into a 2-L vessel and allowed to reach equilibrium. Calculate the equilibrium constant for the reaction if the concentration of Cl2 at equilibrium is 0.08 M. [9 marks] 6. (a) At temperature 25°C, 0.02 M hydrazine, N2H4 solution is 0.69% ionised. Calculate the: (i) Concentration of OH ion. (ii) ionisation constant, Kb. [4 marks]
CHEMISTRY 1 SK015 SESSION 2023/2024 SETARA PSPM1 KOLEJ MARA KULIM 7 (b) A buffer solution with pH 3.50 is produced when sodium benzoate, C6H5COONa is added to 500 mL of 0.2M aqueous benzoic acid, C6H5COOH solution. [Ka for C6H5COOH = 6.3 x10-5] (i) Calculate the mass of sodium benzoate need to be added in forming this buffer. (ii) Explain the buffering effect of adding a small amount of H2SO4 into the buffer solution. [6 marks] (c) When a 1.0 × 10-3 mol dm-3 solution of CaCl2 is mixed with 5.0 × 10-3 mol dm-3 solution of Na2SO4, will precipitate form? (Ksp CaSO4 = 2.0 × 10-5) [4 marks] END OF QUESTION Prepared by: Chemistry Unit, Kolej MARA Kulim Session 2023/2024