Question

1) Define the following:
Standardization, titrant, primary standard, acid/base indicators, indicator range, end point, equivalence point, titration curve, buffer solution. 


2) What are the requirements for a primary standard? 


3) Write the transition range and color change for the following indicators: Phenolphthalein, 
bromocresol green, methyl orange. 


5) What is the aim of standardization? 


6) What is the difference between primary standard and standard solution? 


7) Define and compare end-point and equivalence point. 


8) Why the weak acids cannot be used as titrant in the titrations? 


9) Why do the indicators change their colors for different pH’s. (Hint: Consider the chemical 
behavior of the indicators.) 


10) What is gravimetric titration? How and why is it different than a volumetric titration? 
Which one is more accurate? 


11) What limits the accuracy of a titration? How can you improve it? 


12) How is mass measured? How can one improve the accuracy of the mass measurement?

Answer 1

1. Standardization is the procedure using which we are finding the concentration of the solution with accuracy. Titrant is the solution used in titration with known concentration. Primary standard is a solution which can be prepared with the given concentration easily in the Lab.  

Acid base indicators indicate the acidic/basic nature of the solution by change in colour. The pH range over which an indicator can be used in the titration of acid and base is called as indicator range. The exact stage of titration at which the reactants are completed reacted (base is completely neutralized with acid) is called as end point. Equivalence point in the level in the titration at which the moles of one reactant and moles of another reactant are equal. The graph between volume of titrant and pH of the solution is called as titration curve. The solution which resist the change in pH on adding the slight acid or base is called as buffer solution.

2) Primary standard should be available in purest solid form. It should be easily soluble in water, It should not decompose in room temperature and should not be deliquescent.

3)

Indicator	pH range	colour in acid	colour in base
Phenolphthalein	8.2-10	colourless	pink
Methyl orange	3.2-4,4	red	yellow
Bromcresol	3.5-5.4	yellow	blue

4) The aim of standardization is to find the concentration of secondary standard solutions with the help of primary standard solution before using them in volumetric analysis

5) Primary standard solution is prepared in the lab with the measured mass of reagent. Standard solution concentration is determined by titrating it against primary standard solution.

6) In equivalent point the moles of reactants titrated are exactly equal. In end point the mole of one reactant is a little excess than the moles of another reactant.

7) Weak acids didnot dissociate completely in solution. So they can not be used in volumetric analysis

8) Indicators are weak acids or weak bases. They are existing in two form, dissociated form and undissociated form with different colours. When the pH of the solution is changing they are changing their forms and change their colours.

9) In gravimetric analysis the reactants are precipitated with the reagent and the mass of precipitate is found to determine the concentration of solution. Generally volumetric analysis is more accurate because in gravimetric analysis there is a chance of weight loss.

10) The volume of solutions reacted is the limiting factor for the accuracy of the titration. It can be improved by avoiding the errors while reading, avoiding the spill outside the flask etc.

11) Mass is measured in analytical balance. The accuracy of mass experiment can be improved by avoiding loss in transporting from one container to another, avoiding errors while reading etc.