CHEMISTRY 1922 Saturday, June 24 Answer ten questions as indicated below. 9 a.m.-12 m. Number and letter your answers to correspond to the questions selected. PART I (Answer all questions in Part I.) 1. Indicate in words or by writing an equation a reaction that will illustrate the characteristic behavior of each of the following: (a) an oxidizing agent, (b) a reducing agent, (c) a catalytic agent, (d) a dehydrating agent. Designate, in each case, the substance whose characteristic behavior is illustrated. 2. Write equations for the following reactions, using formulas throughout. Equations must be properly balanced to receive credit. a) Steam passed over heated carbon= b) Solutions of ferric chloride and lead nitrate= c) Zinc oxide and hydrochloric acid= d) Manganese dioxide, sodium chloride, and concentrated sulphuric acid= e) Nitric acid and copper= 3. A sample of crystallized sodium sulphate (Na2SO4 XH2O) weighing 6.7 grams was completely dehydrated. The residue was found to weigh 3.55 grams. Calculate the number of molecules of water in one formula weight of crystallized sodium sulphate. (Atomic weights: S 32, Na 23, O 16, H 1.) 4. a) List the following elements in the order of their activity: copper, hydrogen, iron, silver, zinc. State (1) which will dissolve in dilute sulphuric acid liberating hydrogen, (2) which will copper displace from solution? (3) which will iron displace from solution? b) Describe the properties and uses of hydrogen sulphide and write equations showing how it would react with solutions of two different metallic salts. 5. a) In terms of the ionic theory, state what a water solution of sodium sulphate contains. b) Write the ionic equation representing the neutralization of potassium hydroxide by sulphuric acid. PART II (Answer five questions from Part II. Answers to extra questions will receive no credit.) 6. a) Suppose oxygen to be mixed with an excess of hydrogen, how could they be made to combine? b) State two reasons for believing that a chemical reaction has taken place. c) What experiment would show that no free oxygen is present after the reaction? 7. Name three different metals which are prepared commercially, one from its sulphide, a second from its oxide, and a third by an electrolytic method. Outline briefly the process in any two cases. 8. a) Mention the allotropic forms of two elements. b) For each element give a method by which one allotropic form may be converted into another. c) Show by an example how two allotropic forms of a given element may differ chemically. 9. Tell briefly about the composition of each of the following: (a) soap, (b) steel, (c) water gas, (d) glass, (e) brass. 10. One gram of magnesium, reacting with hydrochloric acid, liberates 933 cc. of hydrogen, measured dry at 0° C. and 760 mm. Calculate the equivalent (combining weight) of magnesium. (One liter of dry hydrogen at 0° C. and 760 mm. weighs 0.09 gram.) 11. A beaker contains a solution of the nitrates of silver, copper, iron, barium, and sodium. Explain how you could detect the presence of each metallic element. Write equations that will illustrate two of the reactions involved. 12. Choose from the following list the substances that will react with water at room temperature and give the formulas of the substances formed: potassium, sodium chloride, gold, calcium carbide, ammonia gas, phosphorous pentoxide. 13. a) Name a solid which is soluble in water, whose solution gives a precipitate with both hydrochloric and sulphuric acid, and which on heating evolves a brown gas. b) Name a solid which is white, gives a violet light when held in the Bunsen flame, and a violet vapor when it is heated with a mixture of manganese dioxide and sulphuric acid. 14. What disadvantages are there in the following situations, and what are the fundamental reasons for these disadvantages? a) Peat as a fuel. b) Kerosene in the carburetor of an automobile. c) Sea water in a lead storage battery in a submarine. d) Inadequate ventilation in coal mines. 15. a) Name two common calcium minerals. b) What substances are used in making (1) lime, (2) plaster of Paris, (3) fertilizers, (4) bleaching powder? c) What geologic changes in limestone regions may result from the action of ground water containing carbon dioxide? CHEMISTRY 1922 Thursday, September 21 Answer ten questions as indicated below. 9 a.m.-12 m. Number and letter your answers to correspond to the questions selected. PART I (Answer all questions in Part I.) 1. In the language of the chemist define or explain the following terms: solution, fractional distillation, effervescence, anhydride, gram molecule (mole), ion. 2. Write equations for the following reactions, using formulas throughout. The equations must be properly balanced to receive credit. a) Ammonium phosphate and calcium hydroxide = b) Chlorine water and sodium iodide= c) Hydrogen sulphide and ammonia= d) Silver sulphate solution and aluminum= e) Calcium acid carbonate and sodium hydroxide = 3. a) What weight of oxygen can be obtained from 245 grams of potassium chlorate ? b) What volume of acetylene (C2H2), measured at 0° C. and 760 mm. can be burned to CO2 and H2O in 64 grams of oxygen ? (Atomic weights: K 39, Cl 35.5, O 16, C 12, H 1. Assume that 22.4 liters of oxygen at 0° C. and 760 mm. weighs 32 grams.) 4. How would you proceed to make (a) a base from sodium, (b) an acid from sulphur? (c) What would be formed if the acid were mixed with an excess of the base? (d) What would be formed if the acid were in large excess? Illustrate your answers by writing equations for the reactions described. What does the above equation mean as regards (1) molecules, (2) atoms, (3) weights, (4) volumes? b) State the laws of Conservation of Mass and of Conservation of Energy and point out how each is illustrated in the following equation: 2H2+O2=2H2O+136,800 calories PART II (Answer five questions from Part II. Answers to extra questions will receive no credit.) 6. Make a labeled diagram of the apparatus used in the preparation and collection of chlorine. Write equations for the reactions involved in this preparation. Explain why each substance is used. Mention two chemical properties of chlorine. 7. Give the common commercial name, the source, and two uses of (a) sodium nitrate, (b) sodium carbonate, (c) calcium oxide, (d) hydrochloric acid. 8. NaCl+H2SO4=HC1+NaHSO4 Under what conditions of experiment would the foregoing reaction be incomplete? By what means can it be made to go to completion ? 9. What precautions are essential to preserve without alteration the following substances: (a) concentrated sulphuric acid, (b) baking powder, (c) silver chloride, (d) solid sodium hydroxide, (e) sulphurous acid solution? Give reasons for the precautions that you mention. 10. a) What weight of anhydrous sodium carbonate (Na2CO3) can take up water to produce 143 grams of crystallized sodium carbonate (Na2CO3 10H2O)? (Atomic weights: Na 23, O 16, C 12, H 1.) b) Forty-four grams of ferrous sulphide (FeS) are heated with an excess of dilute sulphuric acid. What volume of hydrogen sulphide gas (H2S) measured dry at 0° C. and 760 mm. can be obtained? (Atomic weights: Fe 56, S 32, O 16, H 1.) 11. In the blast furnace the reduction of an ore consisting of iron oxide and silica is accomplished with the aid of coke, lime, and air. Explain the part played by each in the process. 12. In what two fundamentally different ways is an electric current useful in the manufacture of commercial chemicals? Illustrate each case with two commercial processes. 13. What chemical tests would you employ to distinguish between (a) dilute hydrogen peroxide and water, (b) a ferrous salt and a ferric salt, (c) copper oxide and manganese dioxide, (d) mercuric oxide and red lead? 14. Give (a) a method of preparation, including the collection or separation of the substance for any three of the following substances, (b) a distinguishing chemical property for any three of the following substances: (1) carbon dioxide, (2) silver chloride, (3) ammonia, (4) hydrogen iodide, (5) sodium acid carbonate. 15. What are the principal products derived from the destructive distillation of soft coal? Indicate the relation of these products to the prosperity of nations by naming one important use for each. |