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Which indicator would be the best to use for a titration between 0.30 M (CH3)2NH with 0.30 M HI? 

1. alizarin yellow R, color change at pH 10-12
2. methyl red, color change at pH 4-6
3. bromothymol blue, color change at pH 6-8
4. thymol blue, color change at pH 8-10
5. phenol red, color change at pH 7-9

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Alyssa Mae Remarim
Alyssa Mae RemarimLv10
25 Dec 2020

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Related questions

Piperazine, C4H10N2, is a diprotic weak base (pKb1 = 4.22 and pKb2 = 8.67). A sample of piperazine is dissolved in 100.0 mL of water and titrated with 0.500 M HCl. It takes 48.00 mL of HCl to reach the second equivalence point.

 

SHOW ALL WORK

 

a) What was the original concentration of the piperazine solution?

b) Calculate the pH after the following amounts of HCl have been added: 0 mL, 12.00mL, 24.00mL,36.00mL, 48.00mL, and 60.00mL

c) Sketch the titration curve for this titration

d) Which of the following indicators could be used to detect the first equivalence point? The second?

     Indicator                              Ka                         Color Change

     ______________________________________________________________

     Bromocresol green             2.5 x 10^-5             yellow => blue-green

     Phenol Red                         2.5 x 10^-8            yellow => red

     Methyl Yellow                     3.5 x 10^-4             red     => yellow

     Alizarin Yellow                     8.9 x 10^-12          yellow => red

Consider the following pH indicators and their pH range:

Methyl orange: 3.2-3.4
Methyl red: 4.8-6.0
Bromothymol blue: 6.0-7.6
Phenolphthalein: 8.2-10.0
Alizarin yellow: 10.1-12.0

Assume an indicator works best when the equivalence point of a titration comes in the middle of the indicator range. Which indicator is the best choice to use when 0.100 M NH3 (Kb = 1.8 X 10^-5) is titrated with 0.100 M HCl?

The answer is Methyl Red but I am confused as to why that is because:

pOH = pKb + log(acid/base) correct?

So, -log(1.8 X10^-5) = 4.74 + 0 = 4.74 = "POH"!

pOH = 4.74

pH = 14 - 4.74 = 9.26, so Phenolphthalein is what I chose.

It chose Methyl red as if 4.74 is the pH? that's the pOH! How did they go from Kb to pH without converting. I am very confused, please advise!

In order to choose an appro[rate indicator, you must know what the pH should be at the equivalence point of your titration.which of the following indicators would be most appropriate to determine the equivalence point for a titration of a weak base [25 mL 0.10 M morpholine (Kb = 3.1E-6)] with a 010 m HCl

A) Bromthymol blue 7 pH

B) Bromocresol purple 6 pH

C) Phenol Red 8 pH

D) Phenolthalein 9 pH

E) Methyl 5 pH

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