Question

1. The indicator used in the titration of HCl and Na, CO, is-----​

Answer 1

Answer:

LITMUS PAPER IS THE BEST INDICATOR

Answer 2

Answer:

methyl orange

Explanation:

Universal indicator - this is a mixture of several indicators. It can indicate pH values of over a range of 3 -11 by successive changes of color - this takes place at every change of one unit of pH.

2. Ordinary single indicator – this requires a change of about two units of pH to show a full color change. The table below gives the three common indicators for acid - alkali titration.

 

Indicator

Acid Side

Neutral

Alkaline Side

Methyl Orange

Pink

Orange

Yellow

Litmus

Red

Purple

Blue

Phenolphthalein

Colorless

Colorless

Pink

Choice of Indicator

 lt is possible to calculate before hand a rough value of the pH of the mixture at end point of an acid/base titration, hence any one of the indicators which give color change at or close to the calculated pH value is suitable to be used for the titration. Therefore, the choice of an indicator in an acid/base titration actually depends on the strength of acids and bases involved and how well the colors can be distinguished by the eyes.

Below are a number of typical acid/base titrations (0.1 M of 25 cm3 of base is titrated upon by 0.1 M of the acid, which is added in small quantities). For a strong acid and a strong base titration (e.g. HCl and NaOH) Methyl orange is a suitable indicator for this titration.

Methyl orange changes color over a pH range of 3.2 - 4.4. At pH of 4.4, methyl orange gives a full color change, indicating the equivalence point. Methyl orange gives color change very close to the equivalence point, with an error of less than 0.1%. Methyl red (pH range of 4.8 - 6.0) is also suitable for strong acid and strong base titrations.

Graphically:

 

Note: - There is a sharp drop in pH near or at the equivalence point. - The titre value, i.e., the volume of acid added at equivalence point is deduced by tracing the almost vertical straight line in the graph to the horizontal axis. For the titration whose graph is plotted, the titre value is 25 cm3.