Chemistry Indicators Problem

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In summary, for the given titrations, the suitable indicators are:1. HNO3 added to NaCN: Methyl orange or Bromocresol green, with a pH range of 3.1-4.4 and 3.8-5.4 respectively.2. LiOH added to HNO2: Thymol blue or Bromocresol purple, with a pH range of 8.0-9.6 and 5.2-6.8 respectively.
  • #1

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?
 
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  • #3


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.
 

1. What are chemistry indicators and why are they important?

Chemistry indicators are substances that change color in the presence of specific chemicals or conditions. They are important because they allow us to visually identify the presence or absence of certain substances in a solution, which can be useful in various scientific and everyday applications.

2. How do chemistry indicators work?

Chemistry indicators work by undergoing a chemical reaction when exposed to specific substances or conditions. This reaction causes a change in the color of the indicator, which can be observed and used to determine the presence or absence of the target substance.

3. What are some common examples of chemistry indicators?

Some common examples of chemistry indicators include litmus paper, phenolphthalein, bromothymol blue, and methyl orange. Litmus paper turns red in the presence of acids and blue in the presence of bases, while phenolphthalein turns pink in the presence of a base and remains colorless in the presence of an acid.

4. Are chemistry indicators always accurate?

No, chemistry indicators are not always accurate. They can be affected by factors such as temperature, concentration, and the presence of other substances in the solution. It is important to use multiple indicators or confirmatory tests to ensure accurate results.

5. What are the limitations of using chemistry indicators?

One limitation of using chemistry indicators is that they can only detect the presence or absence of a specific substance, and not the exact amount present. They also have a limited range of sensitivity and may not detect substances in low concentrations. Additionally, some indicators may not work in certain types of solutions or may give false results due to interfering substances.

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