QUESTIONS AND ANSWERS 11 



Give the chemical sjmibol and the atomic weight of each of the follow- 

 ing: (a) hydrogen, (b) chlorine, (c) iron, (d) mercixry, 

 (e) oxygen. 



(a) H, 1; (b) CI, 35; (c) Fe, 56; (d) Hg, 198.5; (e) 0, 16. 

 Give the chemical name of each of the following: (a) FeCla, (b) 

 NaHC03, (c) CO,, (d) As,03, (e) H3PO,. 

 (a) Ferrous chloride, (b) sodium bicarbonate, (c) carbon diox- 

 ide, (d) arsenic trioxide, (e) phosphoric acid. 

 Write the chemical names of the substances whose formulas are as 

 follows: (a) Ca(OH)„ (b) KCIO3, (c) PH3, (d) KNO3, (e) 

 HgCl, (f) SnCl,, (g) KMnO,, (h) NO, (i) CO, (j) AgNO^. 



(a) Calcium hydroxide, (b) potassium chlorate, (c) phosphine, 

 (d) potassium nitrate, (e) mercurous chloride, (f) stannous chlo- 

 ride, (g) potassium permanganate, (h) nitric oxide, (i) carbon 

 monoxide, (j) silver nitrate. 



Write the graphic formula of (a) sulphuric acid, (b) ammonia, (c) 

 potassium chlorate. 

 W H-OX^O 

 H-0/^^0 



(b) H-N<^ 



(c) Cl-0-O-O-K 



Give two laws relating to chemical combinations. 



1. Law of constant or definite proportions. The same compound 

 is always composed of the same elements in constant proportions by 

 weight. 



2. Law of multiple proportions. When two elements unite to 

 form several compounds the higher proportions of each are even 

 multiples of the lowest. 



Explain fully how the percentage composition of any compound is 

 determined. 

 Obtain the molecular weight of the compound by adding together 

 the atomic weights of the elements it contains. Then, the percentage 

 of any one element is obtained by dividing its atomic weight by the 

 molecular weight. For instance, the molecular weight of KNO3 

 is, 38.82 -f 13.93 + 47.64 = 100.39. The percentage composition 

 of K is 38.82 -f- 100.39, or 38.66 per cent. 

 Define and illustrate the law of definite proportions. 

 Definition given above. 



Sodiiun chloride, NaCl, is always composed of 23 parts by weight 

 of Na and 35.5 parts of CI. 



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