55.  Given the following data:  25 cc. of a hydrochloric acid, when standardized gravimetrically as silver chloride, yields a precipitate weighing 0.5465 gram. 24.35 cc. of the hydrochloric acid are exactly equivalent to 30.17 cc. of KHC_{2}O_{4}.H_{2}C_{2}O_{4}.2H_{2}O solution.  How much water must be added to a liter of the oxalate solution to make it exactly 0.025 N as a reducing agent?

!Answer!:  5564 cc.

56.  Ten grams of a mixture of pure potassium tetroxalate (KHC_{2}O_{4}.H_{2}C_{2}O_{4}.2H_{2}O) and pure oxalic acid (H_{2}C_{2}O_{4}.2H_{2}O) are dissolved in water and diluted to exactly 1000 cc.  The normal value of the oxalate solution when used as an acid is 0.1315.  Calculate the ratio of tetroxalate to oxalate used in making up the solution and the normal value of the solution as a reducing agent.

!Answers!:  2:1; 0.1577 N.

57.  A student standardized a solution of NaOH and one of KMnO_{4} against pure KHC_{2}O_{4}.H_{2}C_{2}O_{4}.2H_{2}O and found the former to be 0.07500 N as an alkali and the latter exactly 0.1 N as an oxidizing agent.  By coincidence, exactly 47.26 cc. were used in each standardization.  Find the ratio of the oxalate used in the NaOH standardization to the oxalate used in the permanganate standardization.

!Answer!:  1:1.

58.  A sample of apatite weighing 0.60 gram is analyzed for its phosphoric anhydride content.  If the phosphate is precipitated as (NH_{4})_{3}Po_{4}.12MoO_{3}, and the precipitate (after solution and reduction of the MoO_{3} to Mo_{24}O_{37}), requires 100 cc. of normal KMnO_{4} to oxidize it back to MoO_{3}, what is the percentage of P_{2}O_{5}?

!Answer!:  33.81%.

59.  In the analysis of a sample of steel weighing 1.881 grams the phosphorus was precipitated with ammonium molybdate and the yellow precipitate was dissolved, reduced and titrated with KMnO_{4}.  If the sample contained 0.025 per cent P and 6.01 cc. of KMnO_{4} were used, to what oxide was the molybdenum reduced? 1 cc.  KMnO_{4} = 0.007188 gram Na_{2}C_{2}O_{4}.

!Answer!:  Mo_{4}O_{5}.

60.  What is the value of 1 cc. of an iodine solution (1 cc. equivalent to 0.0300 gram Na_{2}S_{2}O_{3}) in terms of As_{2}O_{3}?

!Answer!:  0.009385 gram.

61. 48 cc. of a solution of sodium thiosulphate are required to titrate the iodine liberated from an excess of potassium iodide solution by 0.3000 gram of pure Kio_{3}. (Kio_{3} + 5KI + 3H_{2}so_{4} = 3K_{2}so_{4} + 3I_{2} + 3H_{2}O.) What is the normal strength of the sodium thiosulphate and the value of 1 cc. of it in terms of iodine?

!Answers!:  0.1753 N; 0.02224 gram.

62.  One thousand cubic centimeters of 0.1079 N sodium thiosulphate solution is allowed to stand.  One per cent by weight of the thiosulphate is decomposed by the carbonic acid present in the solution.  To what volume must the solution be diluted to make it exactly 0.1 N as a reducing agent? (Na_{2}S_{2}O_{3} + 2H_{2}Co_{3} = H_{2}so_{3} + 2NaHCO_{3} + S.)