ACIDIMETRY AND ALKALIMETRY 11 



If either or both of the solutions should first be diluted with a 

 considerable bulk of pure water, the result on mixing the two would 

 be the same, for the extra amount of water present takes no part 

 in the reaction (except to the extent of absorbing a part of the heat 

 set free). 



The two solutions are equivalent. They also happen to be 

 normal solutions. The hydrochloric acid is normal because it 

 contains 1 gm. of active or replaceable hydrogen per liter of solu- 

 tion, and not because it contains the same number of grams of 

 HC1 per liter as there are units in the molecular weight. The 

 sodium hydroxide solution is normal because it is equivalent to a 

 solution containing 1 gm. of replaceable hydrogen per liter. 



The molecular weight of sulphuric acid is 98. A sulphuric acid 

 solution containing exactly 98 gms. per liter contains therefore the 

 same number of molecules per unit volume as the sodium hydroxide 

 solution containing 40 gms. per liter. But 1 molecule of sulphuric 

 acid requires 2 molecules of sodium hydroxide for the formation 

 of the neutral salt, sodium sulphate, because the sulphuric acid 

 molecule has 2 replaceable hydrogen atoms. The solutions are 

 not equivalent, for the sulphuric acid contains 2 gms. active hydro- 

 gen per liter. It is exactly twice as strong as the sodic hydrate 

 solution; it is a 2 normal solution. 



On the basis of the above description of what constitutes a 

 normal solution, calculate the number of grams per liter in tenth 

 normal sulphuric acid (.IN H^SQi), fifth normal hydrochloric 

 acid (.2 N HC1), half normal oxalic acid (.5 N C 2 H 2 4 , 2H 2 O), 

 fourth normal acetic acid (.25 N CHsCOOH), half normal sodic 

 hydrate (.5 N NaOH), twentieth normal barium hydrate (.05 N 

 Ba(OH 2 ), fifth normal ammonium hydrate (.2 N NH^OH). 



The same description of normal solutions applies to other sub- 

 stances than acids and alkalies, as for example, oxidizing and reduc- 

 ing substances such as potassium permanganate, potassium 

 bichromate, iodine, cupric hydrate, stannous chloride. A normal 

 solution is here one capable of liberating 1 gm. of reducing hydrogen 

 (or of giving off exactly sufficient oxygen to oxidize 1 gm. of hydro- 

 gen) per liter. Potassium permanganate, for example, in the 

 presence of sulphuric acid and some easily oxidizable substance 

 is decomposed as follows: 



2KMnO 4 +3H 2 SO4 = K 2 S0 4 -f 2MnSO 4 + 3H 2 O+5O. 



