In the laboratory we often measure the volume of one solution that is required to react with a given volume of another solution of known concentration. Then we calculate the concentration of the first solution. The process is called

Options

A. neutralization
B. precipitation
C. titration
D. combination

Answer

3

Explanation

Titration is the process in which a solution of one reactant (the titrant) is carefully added to a solution of another reactant and the volume of titrant required for complete reaction is measured.
To know when to stop a titration (i.e., when is the chemical reaction just complete), a few drops of an indicator solution are added to the solution to be titrated. An indicator is a substance that can exist in different forms, with different colours that depend on the concentration of `H^(+)` in the solution. At least one of these forms must be very intensely coloured so that even very small amounts of it can be seen.
We can titrate an acid solution of unknown concentration by adding a standardized solution of sodium hydroxide dropwise from a buret. A common buret is graduated in large intervals of 1 mL and in smaller intervals of `0.1 mL`, so that it is possible to estimate the volume of a solution dispensed to within at least `+- 0.02 mL`. (Experienced individuals can often read a burst to `+- 0.01 mL`.)
The solution `(HCl)` to be titrated is placed in an Erlenmeyer flask (volumetric flask), and a few drops of indictor are added. The analyst tries to choose an indictor that changes color clearly at which stoichiometrically equivalent amounts of acid and base have reacted, the equivalence point. The point at which the indicator changes colour and the titration is stopped is called the end point.
Ideally, the end point should coincide with the equivalence point. Phenolphthalein is colourless in acidic solution and reddish violet in basic solution. In a titration in which a base id added to an acid, phenolphthalein is often used as an indicator. The end point is signaled by the first appearance of a faint pink coloration that persists for at least `15` seconds as the solution is swirled.
The buret is usually filled with a standard solution (or the solution to be standardized). The volume of solution in the buret is read carefully. The meniscus decribes the surface of the liquid in the buret. Aqueous solutions wet glass so the meniscus of an aqueous solution is always concave. The position of the bottom of the meniscus is read and recorded. The volume of the solution is read again after the end point. The difference between the final and initial buret readings is the volume of the solution used.