Suppose that 50.0 mL of 0.25 m CH₃NH₂(aq) is titrated with 0.35 m HCl(aq).

(a) What is the initial pH of the 0.25 m CH₃NH₂(aq)?

(b) What is the pH after the addition of 15.0 mL of 0.35 m HCl(aq)?

(c) What volume of 0.35 m HCl(aq) is required to reach half way to the stoichiometric point?

(d) Calculate the pH at the halfway point.

(e) What volume of 0.35 m HCl(aq) is required to reach the stoichiometric point?

(f) Calculate the pH at the stoichiometric point.

(g) Use Table 6H.2 to select an indicator for the titration.

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TABLE 6H.2 Indicator Color Changes* pH range of color change Indicator thymol blue methyl orange pKin 1.7 3.4 bromophenol blue 3.9 4.7 bromocresol green methyl red 5.0 litmus 6.5 7.1 7.9 8.9 9.4 11.2 11.7 bromothymol blue phenol red thymol blue phenolphthalein alizarin yellow R alizarin 1.2 to 2.8 3.2 to 4.4 3.0 to 4.6 3.8 to 5.4 4.8 to 6.0 5.0 to 8.0 6.0 to 7.6 6.6 to 8.0 8.0 to 9.6 8.2 to 10.0 10.1 to 12.0 11.0 to 12.4 Color of acid form red red yellow yellow red red yellow yellow yellow colorless yellow red Color of base form yellow yellow blue blue yellow blue blue red blue pink red purple