QUESTIONS AND ANSWERS 7 



different gases are separated from each other by some porous sub- 

 stance, such as burned clay, gypsum, etc. 



In the open end of an unglazed clay cylinder (such as is used 

 in galvanic experiments) there is fixed a glass tube about one metre 

 long, its open end terminating in a dish containing water ; the cylin- 

 der and tube are filled with air. Over the porous cylinder is placed 

 a wider vessel filled with hydrogen. The latter presses faster into 

 the cylinder than the air escapes from it; the air in the cylinder 

 and tube is displaced and rises in the water in bubbles. When the 

 escape of gas ceases, the tube and cylinder are almost filled with 

 pure hydrogen. 



State which of the following gases are (a) lighter than air, (b) heavier 

 than air: oxygen, nitrogen, hydrogen, ammonia gas, 

 sulphur dioxide, chlorine. 



(a) Hydrogen, ammonia gas, nitrogen. 



(b) Sulphur dioxide, chlorine, oxygen. 



Distinguish in meaning between the following suffixes when used in 

 names of chemical compounds : (a) ous and ic, (b) ate and 

 ite. Give examples. 



(a) ous indicates that a compound contains less, and ic that it 

 contains more, of the other, or electronegative, element. An ex- 

 planation of these terms involves the subject of valence. Fre- 

 quently, two elements unite to form two or more compounds, for 

 instance, mercury and chlorine unite to form mercurous chloride, 

 HgjCla, and also, mercuric chloride, HgCla. The electropositive 

 atom (mercury) terminates in ous, indicating the lower valence 

 (or a valence of 2 for two atoms), while ic indicates the higher 

 valence (or a valence of 2 for one atom) . 



(b) The sufiSx ite indicates that a salt is derived from an acid, 

 ternunating in ous (as NajSOg, sodium sulphite), and the suffix ate 

 that it is derived from an acid terminating in ic (as NajSOi, sodium 

 sulphate). 



Give the formula and the chemical name of each of the following : (a) 



washing soda, (b) saltpetre, (c) blue vitriol, (d) corrosive 



sublimate, (e) Glauber's salt, (f) Rochelle salt. 



(a) Sodium carbonate, NajCOg, lOHjO. (b) Potassium nitrate, 



KNO3. (c) Copper sulphate, CuSO^. (d) Mercuric chloride, 



HgClj. (e) Sodium sulphate, NaaSO^. (f) Potassium sodium 



tartrate, KNaC^HiOg. 



Distinguish between organic and inorganic compounds. 



Organic compounds contain carbon and therefore, upon burn- 



Digitized by Microsoft® 



