IB Chemistry 2 nd Year Summer Assignment (Test Grade)

Transcription

1 1. The percentage by mass of calcium carbonate in eggshell was determined by adding excess hydrochloric acid to ensure that all the calcium carbonate had reacted. The excess acid left was then titrated with aqueous sodium hydroxide. (a) A student added cm 3 of mol dm 3 HCl to g of eggshell. Calculate the amount, in mol, of HCl added. (b) The excess acid requires cm 3 of mol dm 3 NaOH for neutralization. Calculate the amount, in mol, of acid that is in excess. (c) Determine the amount, in mol, of HCl that reacted with the calcium carbonate in the eggshell. (d) State the equation for the reaction of HCl with the calcium carbonate in the eggshell. (e) Determine the amount, in mol, of calcium carbonate in the sample of the eggshell.

2 (f) Calculate the mass and the percentage by mass of calcium carbonate in the eggshell sample. (3) (g) Deduce one assumption made in arriving at the percentage of calcium carbonate in the eggshell sample. (Total 11 marks) 2. A toxic gas, A, consists of 53.8 % nitrogen and 46.2 % carbon by mass. At 273 K and Pa, g of A occupies 462 cm 3. Determine the empirical formula of A. Calculate the molar mass of the compound and determine its molecular structure. (Total 3 marks)

3 3. Brass is a copper containing alloy with many uses. An analysis is carried out to determine the percentage of copper present in three identical samples of brass. The reactions involved in this analysis are shown below. Step 1: Cu(s) + 2HNO 3 (aq) + 2H + (aq) Cu 2+ (aq) + 2NO 2 (g) + 2H 2 O(l) Step 2: 4I (aq) + 2Cu 2+ (aq) 2CuI(s) + I 2 (aq) Step 3: I 2 (aq) + 2S 2 O 3 2 (aq) 2I (aq) + S 4 O 6 2 (aq) (a) (i) Deduce the change in the oxidation numbers of copper and nitrogen in step 1. Copper: Nitrogen: (ii) Identify the oxidizing agent in step 1. (b) A student carried out this experiment three times, with three identical small brass nails, and obtained the following results. Mass of brass = g ± g Titre Initial volume of mol dm 3 S 2 O 2 3 (± 0.05 cm 3 ) Final volume of mol dm 3 S 2 O 2 3 (± 0.05 cm 3 ) Volume added of mol dm 3 S 2 O 2 3 (± 0.10 cm 3 ) Average volume added of mol dm 3 S 2 O 3 2 (± 0.10 cm 3 ) (i) Calculate the average amount, in mol, of S 2 O 3 2 added in step 3.

4 (ii) Calculate the amount, in mol, of copper present in the brass. (iii) Calculate the mass of copper in the brass. (iv) Calculate the percentage by mass of copper in the brass. (v) The manufacturers claim that the sample of brass contains 44.2 % copper by mass. Determine the percentage error in the result. (c) With reference to its metallic structure, describe how brass conducts electricity. (Total 10 marks) mol of aluminium hydroxide is mixed with mol of sulfuric acid, and the following reaction occurs: 2Al(OH) 3 (s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (aq) + 6H 2 O(l) (a) Determine the limiting reactant

5 (b) Calculate the mass of Al 2 (SO 4 ) 3 produced (c) Determine the amount (in mol) of excess reactant that remains (d) Define a Brønsted-Lowry acid and a Lewis base. Brønsted-Lowry acid... Lewis base... (e) H 2 SO 4 (aq) is a strong acid. State the name and the formula of any weak acid (Total 8 marks) 5. Draw and label an energy level diagram for the hydrogen atom. In your diagram show how the series of lines in the ultraviolet and visible regions of its emission spectrum are produced, clearly labelling each series. (Total 4 marks)

6 6. (a) List the following types of electromagnetic radiation in order of increasing wavelength (shortest first). I. Yellow light II. III. IV. Red light Infrared radiation Ultraviolet radiation... (b) Distinguish between a continuous spectrum and a line spectrum (c) The thinning of the ozone layer increases the amount of UV-B radiation that reaches the Earth s surface. Type of Radiation Wavelength / nm UV-A UV-B Based on the information in the table above explain why UV-B rays are more dangerous than UV-A (3) (Total 5 marks)

7 7. The electron configuration of chromium can be expressed as [Ar]4s x 3d y. (i) Explain what the square brackets around argon, [Ar], represent. (ii) State the values of x and y. x:... y:... (iii) Annotate the diagram below showing the 4s and 3d orbitals for a chromium atom using an arrow, and, to represent a spinning electron. 4s 3d (Total 3 marks) 8. Rubidium contains two stable isotopes, 85 Rb and 87 Rb. The relative atomic mass of rubidium is given in Table 5 of the Data Booklet. (a) Calculate the percentage of each isotope in pure rubidium. State your answers to three significant figures. (b) The percentage of each isotope can be checked experimentally using a mass spectrometer. A vaporized sample of pure rubidium is ionized and then accelerated in a mass spectrometer. Outline how the use of a magnetic field and a detector in the mass spectrometer enables the percentages of the two isotopes to be determined. (3)

8 (c) State the number of electrons and the number of neutrons present in an atom of 87 Rb. Number of electrons: Number of neutrons: (Total 7 marks) 9. The graph below represents the successive ionization energies of sodium. The vertical axis plots log (ionization energy) instead of ionization energy to allow the data to be represented without using an unreasonably long vertical axis. State the full electron configuration of sodium and explain how the successive ionization energy data for sodium are related to its electron configuration. (Total 4 marks)

9 10. Sodium oxide, Na 2 O, is a white solid with a high melting point. (a) Explain why solid sodium oxide is a non-conductor of electricity. (b) Molten sodium oxide is a good conductor of electricity. State the half-equation for the reaction occurring at the positive electrode during the electrolysis of molten sodium oxide. (c) (i) State the acid-base nature of sodium oxide. (ii) State the equation for the reaction of sodium oxide with water. (Total 4 marks) 11. Consider the bonding and structure of the period 3 elements. (a) Explain the increase in the melting point from sodium to aluminium. (b) Explain why sulfur, S 8, has a higher melting point than phosphorus, P 4.

10 (c) Explain why silicon has the highest melting point and argon has the lowest melting point. (Total 6 marks) 12. (a) (i) Draw the shape of the p z orbital using the coordinates shown. (ii) State the electron configuration of Fe 3+. (iii) Define the term ligand. (iv) Explain why the complex [Fe(H 2 O) 6 ] 3+ is coloured. (3)

11 (v) The element selenium (Z = 34) has electrons in the 4s, 3d and 4p orbitals. Draw an orbital box diagram (arrow-in-box notation) to represent these electrons. (Total 7 marks) 13. (i) Draw the Lewis structures for carbon monoxide, CO, carbon dioxide, CO 2 and methanol, CH 3 OH. (3) (ii) List, with an explanation, the three compounds in order of increasing carbon to oxygen bond length (shortest first). 14. Explain why silicon dioxide is a solid and carbon dioxide is a gas at room temperature (Total 5 marks)... (Total 2 marks) 15. Explain, using diagrams, why CO and NO 2 are polar molecules but CO 2 is a non-polar molecule. (Total 5 marks)

12 16. The graph below illustrates how the vapour pressures of ethoxyethane, CH 3 CH 2 OCH 2 CH 3, benzene, C 6 H 6, and water, H 2 O, change with temperature. (a) Using data from the graph, explain the difference in vapour pressure of ethoxyethane, benzene and water at 30 C.....(4) (b) Use the graph to determine the boiling point of benzene at standard pressure. (Total 5 marks)

13 17. Methoxymethane, CH 3 OCH 3, and ethanol, C 2 H 5 OH, have the same relative molecular mass. Explain why methoxymethane has a much lower boiling point than ethanol (Total 3 marks) 18. PF 3, SF 2 and SiF 4 have different shapes. Draw their Lewis structures and use the VSEPR theory to predict the name of the shape of each molecule. PF 3 SF 2 SiF 4 Lewis structure Name of shape (Total 6 marks) 19. One important property of a rocket fuel mixture is the large volume of gaseous products formed which provide thrust. Hydrazine, N 2 H 4, is often used as a rocket fuel. The combustion of hydrazine is represented by the equation below. N 2 H 4 (g) + O 2 (g) N 2 (g) + 2H 2 O(g) H c O = 585 kj mol 1 (a) Hydrazine reacts with fluorine to produce nitrogen and hydrogen fluoride, all in the gaseous state. State an equation for the reaction.

14 (b) Draw the Lewis structures for hydrazine and nitrogen. (c) Use the average bond enthalpies given in Table 10 of the Data Booklet to determine the enthalpy change for the reaction in part (a) above. (3) (d) Based on your answers to parts (a) and (c), suggest whether a mixture of hydrazine and fluorine is a better rocket fuel than a mixture of hydrazine and oxygen. (Total 9 marks)

15 20. Propene can be hydrogenated in the presence of a nickel catalyst to form propane. Use the data below to answer the questions that follow. Compound Formula H O f / kj mol 1 S O / J K 1 mol 1 hydrogen H 2 (g) propane C 3 H 8 (g) propene C 3 H 6 (g) (i) Outline why the value for the standard enthalpy change of formation of hydrogen is zero. (ii) Calculate the standard enthalpy change for the hydrogenation of propene. (iii) Calculate the standard entropy change for the hydrogenation of propene. (iv) Determine the value of G O for the hydrogenation of propene at 298 K.

16 (v) At 298 K the hydrogenation of propene is a spontaneous process. Determine the temperature above which propane will spontaneously decompose into propene and hydrogen. (Total 9 marks) 21. Consider the following equilibrium. 2SO 2 (g) + O 2 (g) 2SO 3 (g) ΔH o = 198 kj mol 1 (i) Deduce the equilibrium constant expression, K c, for the reaction. (ii) State and explain the effect of increasing the temperature on the yield of sulfur trioxide. (iii) State the effect of a catalyst on the value of K c. (iv) State and explain the effect of a catalyst on the position of equilibrium. (Total 6 marks)

17 22. Nitrogen monoxide reacts at 1280 C with hydrogen to form nitrogen and water. All reactants and products are in the gaseous phase. (i) The kinetics of the reaction were studied at this temperature. The table shows the initial rate of reaction for different concentrations of each reactant. experiment [NO(g)]/ mol dm [H 2 (g)]/ mol dm Initial rate/ mol dm 3 s Deduce the order of the reaction with respect to NO and H 2, and explain your reasoning. (4) (ii) Deduce the rate expression for the reaction. (iii) Determine the value of the rate constant for the reaction from Experiment 3 and state its units. (Total 7 marks)

18 *You will have a quiz over these functional groups the first day back to class. You will have to identify and/or draw these. *You will have a test the 2 nd week of school that includes questions directly from this packet.