Question

What is the principle of limit testing for chloride?

Answer 1

Hint: In general, a limit test is a quantitative or semiquantitative test that is used to detect and control small amounts of impurity that are expected to be present in a substance. A limit test is used to determine how much inorganic contamination is present in a chemical.

Complete Step by Step Solution:
A chlorine atom can have either a positive or negative charge when it creates a chloride ion. Ions are charged atoms or atoms that have gained or lost an electron. An ion obtains a positive charge when it loses an electron and a negative charge when it gains an electron. To obtain a noble gas configuration, an atom produces an ion.
Metals typically lose electrons more quickly than nonmetals, resulting in positive ions or cations. When non-metals gain electrons, they become negatively charged, or anion.
The purpose of a limit test is to find contaminants in a substance and compare them to a standard.

Importance of Limit tests:
(i) To find out the harmful amount of impurities
(ii) To find out the avoidable/unavoidable amount of impurities

Principle:
The silver chloride limit test is based on the reaction of soluble chloride with silver nitrate in the presence of dilute nitric acid to form silver chloride, which appears as solid particles in the solution (opalescence).
The reaction is as follows:
\[Cl + AgN{O_3}\xrightarrow{{dil{\text{ }}HN{O_3}}}AgCl + N{O_3}\]

Additional Information:
The sample solution's opalescence should not surpass that of the control solution. The sample will pass the chloride limit test if the opalescence of the sample solution is less than that of the standard solution, and vice versa.

Note: Nitric acid is added to the chloride limit test to make the solution acidic and to aid silver chloride precipitation, which causes the solution to become turbid at the end of the process.