Question

1) What were the primary standards used for each standardization? Could you use them interchangeably? Why should we pay attention to the mass of the primary standard in the standardization of NaOH and HCl?

2) Why do we boil and then cool the distilled water before preparation of NaOH? Why this process is not necessary for the preparation of HCl?

3) In the titration of weak acid with a strong base why did you use phenolphthalein as indicator?

4) For the titration of a strong acid a neutral range indicator is used and for the titration of weak acids a basic range indicator is used. However, for the titration of their mixture you used an indicator of acidic range for the first end-point. Why?

5) Is volumetric titration or gravimetric titration more accurate? Which one is more precise? Discuss the differences. (Try to use your replicate data and the standard deviation)

6) What are the sources of error in gravimetric titration vs. volumetric titration? Which one would be more dominant?

7) Consider automating a volumetric titration vs. a gravimetric titration, which one would be easier to do?

Answer 1

1) Answer:

Primary standards are which can be weight easily. Based on this we can know the number of moles of the pure compound.

It is used generally in Analytical chemistry.

primary standard includes:

1) Purity of the compound

2) Stability of the compound

3) Low hygroscopic nature

If the compound is the hygroscopic, moisture will attack and the weight of the compound increases that leads to error in the weight.

4) High equivalent weight (minimum weight error).

Standardization of NaOH and HCl:

NaoH and HCl are hygroscopic in nature, As a result of this the moisture content increses and the weight increses. This becomes the error in the weight.

2) Answer:

NaoH is the solid in nature. In the hot condition it can be easily soluble in the water. For the solubility purpose we can heat the water then cool after dissolving the NaOH.

The HCl is the gas in nature. It can be soluble in the water under cold condition.

Note: If we heat the water the solubility rate of the HCl decrease because it is the gaseous compound.

3) Answer:

phenolphthalein as indicator:

Weak acid vs strong base :

Weak acids can not dissociates completely in to its ions, The equilibrium can be seen between the compound and the ions.

AH A^- + H⁺

The strong base can dissociates completely in to its ions. We can see the free Hydroxyl ions (-OH).

BOH   B⁺ + ^-OH

phenolphthalein indicator is the weak acid it can produce the H⁺ ions. These ions can reacts with the Hydroxyl ions (-OH) of the strong base.

Hence phenolphthalein indicator used in the weak acid strong base titration.

4) Answer:

Indicators works based on the phenomenon of P^H. The Acids are having the lower P^H values hence for the first end point acidic range indicators are used.