Titration:—

In presence of a suitable indicator, the volumetric analysis in which a standard solution is added in another solution (whose strength is not known) to reach its end point to determine the strength of that solution is called ‘titration’.

What is primary standard?

A primary standard is a solution of which a concentrated is made from a primary standard. I.E. the substance available in a sufficiently pure from which requires no determination of concentration. A primary standard is one that can be determined to a high level of precision, and reliability. For instance, a typical acid-base titration can be done to determine the concentration of an unknown HCl solution. When titrated against NaOH there will be some uncertainty because of the lack of reliability of the NaOH concentration. For example sodium chloride is an example of a primary standard. This is because it can be obtained very pure. 

What is a secondary standard solution?

A secondary standard solution is a solution which must be standardised first against a primary standard and afterwards it will be stable enough for titrimetric work. Potassium permanganate is an example of a secondary standard. It has to be standardised first, but then it can be used for quantitative analysis,

Indicator:—

In our acid-base titration there is an important use of indicator. An ‘indicator’ is a chemical substance that detects the equivalent point (i.e. the end point) of reaction by changing its color. Indicators have different structures in acidic and in basic solution.

Equivalent Point:—

The ‘equivalent point’ is the point in a titration when a stoichiometric amount of reactant has been added.

Normality:

The number of gram equivalent weight of a solute per liter of solution is called normality.

Normality (N) = gm equivalent of solute /liters per solution.

Back titration[edit]

Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid

Buffer Solution

A buffer (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and itsconjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it and thus it is used to prevent changes in the pH of a solution. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively small pH range so they utilize a buffer solution to maintain a constant pH. One example of a buffer solution found in nature is blood.

What is the difference between Equivalence Point and End Point?• The equivalence point in a titration is the point at which the added titrant is chemically equivalent completely to the analyte in the sample. End point is the point where the indicator changes its color.• Equivalence point comes before the end point.• To get the same equivalent point as the end point, pH of the indicator should match the pH at the equivalence.

Self Indicator

Potassium Permanganate is a good example for this category. Many a times the titrant itself may be so strongly coloured that after the Equivalence point, a single drop of the titrant will impart a definite Pink colour at the END-Point of titration. Ceric sulphate (Pale Yellow) and Iodine (Brown) are other examples of this category. The only disadvantage of Self-Indicators is that a slight over titration always occurs.

External Indicator

They are based on some visible reaction of the titrated substances with a suitable reagent, so that the end Point is marked by failure to elicit the reaction. E.g.. Potassium Ferricyanide the titration of Ferrous iron by K2Cr2O7.Drops of the solution removed to a spotting tile during titration will give a deep purssian blue colour with potassium ferricyanide because ferrous ions are still present. at the end point, ferric ions are present and this does not give a colour with potassium ferricyanide.

E.g. – Starch in case of Iodimetry.

Ferrin Complex in case of Cerimetry.

Internal Indicators

Redox Indicator are substances which have different colours in their Oxidized and Reduced form. The reaction is Reversible. Most of the Redox Indicators are Dyes, the reduced or leuco forms of which are Colourless.