Chemistry

posted by .

Which of the following acid-base indicators should be used for the titration of NH3 with HBr? Kb of ammonia is 1.8 ×10−5.

1. Methyl red, color change red/yellow at 4.4 < pH < 6.2 correct

2. Any of these is suitable.

3. None of these is suitable.

4. Phenolphthalein, color change colorless/red-violet 8.0 < pH <10.0

5. Neutral red, color change red/yellow 6.8 < pH < 8.0

Why is answer choice 1 correct?

  • Chemistry -

    In the titration of a weak base with a strong base, the equivalence point occurs on the acid side of 7.0. That tells you that 5,4,3, and 2 must be wrong and that the correct answer is #1. However, if you wish to calculate it that can be done, too. The pH at the equivalence point is determined by the salt, in this case NH4Br. The NH4^+ is hydrolyzed to
    NH4^+ + H2O ==> H3O^+ + NH3
    Ka = (Kw/Kb) = (H3O^+)(NH3)/(NH4^+)
    You know Kw = 1E-14.
    Kb = 1.8E-5 (for NH3)
    (H3O^+) = x = (NH3)
    (NH4^+) is about 0.05 if you titrate 0.1M HBr and 0.1M NH3. Work it out. I get (H^+) = 7.45E-6 and the H = about 5.13. That falls just about half-way between the limits of 4.4 and 6.2.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. chemistry AP

    methyl red has the following color changes red 4.2 -8.3 yellow a)write the ionic equilibrium equation b) If a small quantity of methyl red is placed in a solution with a pH of 4.5 . calculate the approximate value of [In]/[HIn]. What …
  2. college chemistry

    In the analysis of food, the nitrogen from the protein is sometimes converted into ammonia which is titrated against a strong acid. Given that the final NH3 concentration (approximate) is 0.2M and that pKa for NH4+ is 9.2, choose the …
  3. CHEMISTRY

    In the analysis of food, the nitrogen from the protein is sometimes converted into ammonia which is titrated against a strong acid. Given that the final NH3 concentration (approximate) is 0.2M and that pKa for NH4+ is 9.2, choose the …
  4. chemistry 12

    If the pH of a solution is 3.5, what colour will be shown by each of the following indicators in the solution?
  5. AP CHEMISTRY

    The following acid-base indicators are available to follow the titration. Which of them would be most appropriate for signaling the endpoint of the titration?
  6. AP CHEMISTRY

    The following acid-base indicators are available to follow the titration. Which of them would be most appropriate for signaling the endpoint of the titration?
  7. Chemistry

    Imagine that you needed to choose an indicator for the titration of a strong base (like NaOH) with a strong acid (like HNO3). You have the indicators in Table 1 available. Which indicator would you choose?
  8. Chemistry 20 titration

    1) oi50 . tinypic . com / ejh6vm . jpg The most suitable indicator for the titration is: A)methyl violet B)chlorophenol red C)methyl orange D)phenolphthalein 2-A base is titrated with an acid solution until the indicator changes colour. …
  9. The principles of color

    Which one of these color combinations is a complementary color scheme A. Yellow and violet B. red, red-orange ,and orange C. Red and yellow D. Yellow,green, and blue
  10. CHEMISTRY

    What indicator is better in the following titrations : 1) strong acid/strong base a) methyl red (4.4 - 6.2 ) b) bromophenol blue (6.2 - 7.6 ) 2) strong acid/weak base a) methyl orange (3.1 - 4.4 ) b) bromophenol blue (3.0 - 4.6 ) 3) …

More Similar Questions