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I am Lyosha [343]
3 years ago
7

Which statement is incorrect?

Chemistry
1 answer:
Katena32 [7]3 years ago
4 0

Answer:

e. When the indicator changes color and remains, 2 more drops of the solution in the buret should be added.

Explanation:

<em>Which statement is incorrect? </em>

<em>Select one: </em>

<em> a. The volume of solution in the buret should be recorded when the endpoint is reached. </em> CORRECT. At the endpoint, the titrant is expected to have completely reacted with the titrand.

<em>b. It is good practice to place the flask over a white background to better observe the color change of the solution.</em>  CORRECT. Using a white background makes it easier to detect the changes in the color of the indicator.

<em>c. The endpoint is when the indicator changes color.</em> CORRECT. This is the function of an indicator.

<em>d. Phenolphthalein will go from a colorless solution to a pink solution for the addition of NaOH to an acid solution.</em>  CORRECT. Phenolphthalein is colorless when pH < 8.3 and it is pink when pH > 10.0.

<em>e. When the indicator changes color and remains, 2 more drops of the solution in the buret should be added.</em> INCORRECT. When the endpoint is reached, no more titrant should be added.

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What is the pH of 0.26 M ammonium ion? NH4+(aq) + H2O(1) NH3(aq) + H30* (aq) a. 4.33 b.9.25 c. 3.87 d. 4.92 e. 4.75
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Answer:

b) pH = 9.25

Explanation:

  • NH4+(aq)  +  H2O(l)  ↔  NH3(aq)  +  H3O+(aq)
  • NH3 + H2O ↔ NH4+  +  OH-
  • 2 H2O ↔ H3O+  +  OH-

⇒ Kb = [ NH4+ ] * [ OH- ] / [ NH3 ] = 1.86 E-5......from literature

mass balance NH4+:

⇒ M NH4+ = [ NH4+ ] - [ OH- ]

∴ [ NH3 ] ≅ M NH4+ = 0.26 M

⇒ Kb = (( 0.26 + [ OH- ] )) * [ OH- ] / 0.26 = 1.86 E-5

⇒ 0.26 [ OH-] + [ OH- ]² = 4.836 E-6

⇒ [ OH- ]² + 0.26 [ OH- ] - 4.836 E-6 = 0

⇒ [ OH- ] = 1.859 E-5 M

⇒ pOH = - Log ( 1.859 E-5 )

⇒ pOH = 4.7305

⇒ pH = 14 - pOH = 9.269

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