2. Suppose that the identification labels fell off three of the Beral pipets in

Question

2. Suppose that the identification labels fell off three of the Beral pipets in the set used in this experiment. You realize that the pipets with the missing labels hold NH CI, HCl, and NaCl solutions. Describe an experi- ment you could perform, using these three solutions and any two of the indicators used in this experiment, not including the Universal Indicator, that would allovw you to correctly relabel the pipets. If the data from your experiment would be inconclusive, state the pH range for which you would need an indicator to make certain of the identifications.

Explanation / Answer

Indication of NaCl:

Sine it a salt of a strong acid (HCl) and strong base (NaOH) it does not undergo either anionic or cationic hydrolysis. Hence its pH will be exalty 7.

NH4Cl is a salt of weak base (NH4OH) and strong acid (HCl). Hence it solution undergoes cationic hydrolysis, therefore acidic and pH will be less than 7.

Whereas HCl is completely hence its pH will also be less than 7.

Addition of weak basic indicators like methyl orange (pH range 3.1 to 4.5) or methyl red (pH range 4.2 to 6.3) can show the difference between NaCl and other two acidic solutions.

HCl and NH4Cl can be distinguished by titrating against strong base like NaOH. HCl being strong acid will have end point atexactly pH=7. Either methyl orange ormethyl red can indicate the end point.

For NH4Cl end point will be between the pH range of 11 - 13. Hence indicator like thymol bluecan be used.

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