40.  A sodium hydroxide solution (made from solid NaOH which has been exposed to the air) was titrated against a standard acid using methyl orange as an indicator, and was found to be exactly 0.1 N. This solution was used in the analysis of a material sold at 2 cents per pound per cent of an acid constituent A, and always mixed so that it was supposed to contain 15% of A, on the basis of the analyst’s report.  Owing to the carelessness of the analyst’s assistant, the sodium hydroxide solution was used with phenolphthalein as an indicator in cold solution in making the analyses.  The concern manufacturing this material sells 600 tons per year, and when the mistake was discovered it was estimated that at the end of a year the error in the use of indicators would either cost them or their customers $6000.  Who would lose and why?  Assuming the impure NaOH used originally in making the titrating solution consisted of NaOH and Na_{2}Co_{3} only, what per cent of each was present?

!Answers!:  Customer lost; 3.94% Na_{2}Co_{3}; 96.06% NaOH.

41.  In the standardization of a K_{2}Cr_{2}O_{7} solution against iron wire, 99.85% pure, 42.42 cc. of the solution were added.  The weight of the wire used was 0.22 gram. 3.27 cc. of a ferrous sulphate solution having a normal value as a reducing agent of 0.1011 were added to complete the titration.  Calculate the normal value of the K_{2}Cr_{2}O_{7}.

!Answer!:  0.1006 N.

42.  What weight of iron ore containing 56.2% Fe should be taken to standardize an approximately 0.1 N oxidizing solution, if not more than 47 cc. are to be used?

!Answer!:  0.4667 gram.

43.  One tenth gram of iron wire, 99.78% pure, is dissolved in hydrochloric acid and the iron oxidized completely with bromine water.  How many grams of stannous chloride are there in a liter of solution if it requires 9.47 cc. to just reduce the iron in the above?  What is the normal value of the stannous chloride solution as a reducing agent?

!Answer!:  17.92 grams; 0.1888 N.

44.  One gram of an oxide of iron is fused with potassium acid sulphate and the fusion dissolved in acid.  The iron is reduced with stannous chloride, mercuric chloride is added, and the iron titrated with a normal K_{2}Cr_{2}O_{7} solution. 12.94 cc. were used.  What is the formula of the oxide, FeO, Fe_{2}O_{3}, or Fe_{3}O_{4}?

!Answer!:  Fe_{3}O_{4}.

45.  If an element has 98 for its atomic weight, and after reduction with stannous chloride could be oxidized by bichromate to a state corresponding to an XO_{4}^{-} anion, compute the oxide, or valence, corresponding to the reduced state from the following data:  0.3266 gram of the pure element, after being dissolved, was reduced with stannous chloride and oxidized by 40 cc. of K_{2}Cr_{2}O_{7}, of which one cc. = 0.1960 gram of FeSO_{4}(NH_{4})_{2}so_{4}.6H_{2}O.

!Answer!:  Monovalent.