COMPOUNDS MIXTURES VALENCE, ETC. 21 



In writing such equations, first indicate this change. 

 Thus, in the case of the reaction between nitric acid and 

 copper hydroxide, 



HN0 3 +Cu(OH) = CuN0 3 +HOH. 



Then indicate the bonds of the different radicals and ele- 

 ments 



H(N0 3 ) / +Cu"(OH)' = Cu' / (N0 3 ) / +H // (OH)'. 



Next correct the formulas by noting the bonds and em- 

 ploying the criss-cross rule, 



HN0 3 +Cu(OH) 2 = Cu(NO 3 ) 2 +HOH. 



Select one of the more complicated formulas, such as 

 Cu(NO 3 )2, and check off its parts to see if an equal number 

 of such parts appear on the other side of the equation. 

 Note that it has two (NO 3 ) radicals, which, to balance the 

 equation, must appear in the left-hand, or factor side of 

 the equation: so take 2HN0 3 . Likewise note the two OH 

 of Cu(OH)2, and provide for their appearance on the 

 right or product side of the equation, i.e., 2HOH. The 

 equation now becomes, 



2HNO 3 +Cu(OH) 2 = Cu(N0 3 ) 2 +2HOH. 



Finally, check off each element or radical and see that it 

 appears an equal number of times on each side of the 

 equation. The equation then balances and will be correct. 



In a similar manner, the equation expressing the reac- 

 tion between the two salts, antimony sulphide and sulphuric 

 acid may be balanced. 



SbS + H 2 S0 4 = SbSO 4 + H 2 S (exchanging radicals) , 

 Sb'"S"+H 2 SO 4 = Sb'"(SO 4 )"+H'S" (indicating bonds), 

 Sb 2 S 3 +H 2 SO 4 = Sb 2 (SO 4 ) 3 +H 2 S (correcting formulas), 

 Sb 2 S 3 +3H 2 SO 4 = Sb 2 (SO 4 ) 3 +3H 2 S (balancing and checking 

 off). 



