!Answer!:  35.61 N.

19.  A sample of Rochelle Salt (KNaC_{4}H_{4}O_{6}.4H_{2}O), after ignition in platinum to convert it to the double carbonate, is titrated with sulphuric acid, using methyl orange as an indicator.  From the following data calculate the percentage purity of the sample: 

Wt. sample = 0.9500 gram
H_{2}so_{4} used = 43.65 cc. 
NaOH used = 1.72 cc.
1 cc.  H_{2}so_{4} = 1.064 cc.  NaOH
Normal value NaOH = 0.1321 N.

!Answer!:  87.72 cc.

20.  One gram of a mixture of 50% sodium carbonate and 50% potassium carbonate is dissolved in water, and 17.36 cc. of 1.075 N acid is added.  Is the resulting solution acid or alkaline?  How many cubic centimeters of 1.075 N acid or alkali will have to be added to make the solution exactly neutral?

!Answers!:  Acid; 1.86 cc. alkali.

21.  In preparing an alkaline solution for use in volumetric work, an analyst, because of shortage of chemicals, mixed exactly 46.32 grams of pure Koh and 27.64 grams of pure NaOH, and after dissolving in water, diluted the solution to exactly one liter.  How many cubic centimeters of 1.022 N hydrochloric acid are necessary to neutralize 50 cc. of the basic solution?

!Answer!:  74.18 cc.

22.  One gram of crude ammonium salt is treated with strong potassium hydroxide solution.  The ammonia liberated is distilled and collected in 50 cc. of 0.5 N acid and the excess titrated with 1.55 cc. of 0.5 N sodium hydroxide.  Calculate the percentage of NH_{3} in the sample.

!Answer!:  41.17%.

23.  In titrating solutions of alkali carbonates in the presence of phenolphthalein, the color change takes place when the carbonate has been converted to bicarbonate.  In the presence of methyl orange, the color change takes place only when the carbonate has been completely neutralized.  From the following data, calculate the percentages of Na_{2}Co_{3} and NaOH in an impure mixture.  Weight of sample, 1.500 grams; HCl (0.5 N) required for phenolphthalein end-point, 28.85 cc.; HCl (0.5 N) required to complete the titration after adding methyl orange, 23.85 cc.

!Answers!:  6.67% NaOH; 84.28% Na_{2}Co_{3}.

24.  A sample of sodium carbonate containing sodium hydroxide weighs 1.179 grams.  It is titrated with 0.30 N hydrochloric acid, using phenolphthalein in cold solution as an indicator and becomes colorless after the addition of 48.16 cc.  Methyl orange is added and 24.08 cc. are needed for complete neutralization.  What is the percentage of NaOH and Na_{2}Co_{3}?

!Answers!:  24.50% NaOH; 64.92% Na_{2}Co_{3}.

25.  From the following data, calculate the percentages of Na_{2}Co_{3} and NaHCO_{3} in an impure mixture.  Weight of sample 1.000 gram; volume of 0.25 N hydrochloric acid required for phenolphthalein end-point, 26.40 cc.; after adding an excess of acid and boiling out the carbon dioxide, the total volume of 0.25 N hydrochloric acid required for phenolphthalein end-point, 67.10 cc.