Chemistry Indicators Problem

[Fusilli_Jerry89]

Homework Statement

Select a suitable indicator for each of the following titrations:
HNO3 added to NaCN

LiOH added to HNO2

Homework Equations

all i know is Ka(HIn)=[H3O] at transition point and pKa(HIn)=pH at transition point

The Attempt at a Solution

the book I have is really skimpy on this, and is has no other information, or even an example.

For LiOH + HNO2 <----> H20 + LiNO2
ic that Li doesn't hydrolyze and NO2 does. the ka for NO2 is 5.1E-4 which should also be the Ka then I -log(5.1E-4) and I get the wrong answer? The answer should be an indicator with a pH range around 8-10. I don't get it, can someone please help me?

 

[Borek]

First, calculate pH of the salt which is present in the solution at equivalence point. Second, select correct pH indicator.

 

[Blueshift5]

For the titration of HNO3 and NaCN, a suitable indicator would be methyl orange. This indicator has a pH range of 3.1-4.4, which is within the expected pH range of the titration (pH 3-5).

For the titration of LiOH and HNO2, a suitable indicator would be bromocresol green. This indicator has a pH range of 3.8-5.4, which is within the expected pH range of the titration (pH 4-6). This indicator is also suitable because it has a color change in the range of 8-10, as desired in the problem.

Remember, when selecting an indicator for a titration, it is important to choose one with a pH range that is close to the expected pH range of the titration, and also a color change that occurs within the desired pH range. Other factors to consider include the strength of the acid and base being titrated, and the concentration of the solutions.