7. Classify in natural groups the following elements: carbon, calcium, chlorine, 



barium, bromine, iodine, and silicon. Indicate the relations of those within 

 each group by comparing the formulas and the properties of their oxides 

 or hydrides or both. 



8. Answer any two of the following questions: 



a) Why does a water solution of ferric chloride give an acid reaction, while 



one of sodium carbonate gives an alkaline reaction ? 



b) Account for the fact that a solution of common salt in water conducts 



the electric current, while one of sugar does not. 



c) Which exhibits the greater osmotic pressure, a gram-molecular solution 



of salt or one of cane sugar ? Why ? Sketch an apparatus for demon- 

 strating osmotic pressure. 



9. a) How would you proceed in order to get large crystals from a solution ? 



Small ones ? 

 b) Why do certain crystalline substances on exposure to the air crumble 

 while others do not ? 



Group B 

 (Answer one question from this group.) 



10. At standard temperature and pressure, one liter of the gaseous element, A, 



unites with three liters of the gaseous element, B, to make two liters of the 

 gas, C. If each molecule of C contains one atom of A , what is the simplest 

 formula for a molecule of the element A ? Show clearly how you arrive at 

 your conclusion. 



11. One gram of pure iron forms i .43 gm. of an oxide. Find (a) the percentage 



composition for this oxide of iron, (6) its simplest formula, and (c) the 

 equivalent weight of iron in the compound. (Fe= 56, O = 16.) 



Group C 

 (Answer two questions from this group.) 



12. How would you determine by chemical tests whether (a) "woolen" goods 



contained cotton, (b) baking powder contained ammonium compounds, 

 (c) water contained chlorides ? 



13. a) State the composition of two kinds of baking powder. 



b) Write an equation for the reaction which occurs when one of these 



powders is moistened with water. 



c) Explain the action of yeast in bread-making. 



14. a) Mention two compounds of nitrogen that are used as fertilizers. 



b) Wliat natural provision is there for converting the nitrogen of the air 



into plant food ? 



c) Outline one artificial process for the fixation of atmospheric nitrogen. 



15. Give the method of keeping and the necessary precautions in the storage 



of each of the following substances: (a) sodium, (b) gasoline, (c) yellow 

 (white) phosphorus, (d) bromine, (e) hydrofluoric acid. 



39 



