Test for Potassium Ions (Radical)

Theoretical Background / Context

• Potassium is the seventh abundant metallic element on Earth.

• It is a member of the alkali metals group that is located in the first group of the periodic table. Its chemical symbol is K.

• Potassium has a white silver metallic appearance.

• Pure potassium is highly oxidizable and it can react with air quickly leading to losing its metallic appearance.

• That is why it should be preserved using oil grease.

• Potassium compounds are used in various chemical reactions, preparation of chemicals and medications, etc.

The Abundance of Potassium in Nature:

• Potassium is abundant in nature as potassium ions in mineral salts such as potassium chloride. It is commonly found as a constituent in Earth's crust.

Preparation of Potassium:

• Potassium can be prepared from some potassium containing compounds such as potassium carbonate, potassium chloride and potassium nitride.

K2CO3+2C⟶3CO+2K

2KCl+CaC2⟶CaCl2+2C+K

2KN3⟶3N2+2K

• However, all of the previous reactions require high energy input and are considered to be highly expensive, so cheaper procedures are commonly followed to obtain pure potassium through reduction of some potassium salts such as potassium chloride.

KCl + Na ⟶ K + NaCl

Properties and Uses of Potassium:

• Potassium is metal that has a boiling point of 63.65⁰C.

• Therefore, its molten form can be used as a cooling agent for nuclear reactors.

• In addition, it is being used in the research of pharmaceutical industries as well as some energy applications.

• It is used as the basic radical for the preparation of various chemicals that include potassium hydroxide, potassium carbonate, potassium permanganate, etc.

Potassium Salts:

• Potassium containing compounds are used in different applications such as potassium hydroxide that is used in the manufacturing of soaps and detergents, potassium carbonate that is used in glass manufacturing, and potassium chloride that is used in pharmaceutical preparations, baking, photography, tanning leathers, and food additives.

• Potassium chloride whose chemical formula is KCl is considered to be the most abundant potassium salt. It is composed of potassium and chloride ions in the ratio of 1:1.

The Abundance of Natural Potassium Chloride:

• Potassium chloride is existent in nature as the mineral sylvite.

• It is easily and cheaply prepared as it can be prepared by treating any potassium base such as potassium hydroxide with hydrochloric acid.

KOH + HCl → KCl + H2O

Properties and Uses of Potassium Chloride:

• Potassium chloride is a white crystalline salt that is highly soluble in water producing colorless aqueous solutions.

• Potassium chloride has the chemical formula of KCl with a molecular weight of 74.55 g/mol.

• Potassium chloride salt possesses a melting point and boiling point of 770 ⁰C and 1420 ⁰C, respectively.

• Potassium chloride plays an important role in the manufacture of fertilizers. Like sodium chloride, potassium chloride regulates muscle contractions, nerve impulses and represents a part of the body fluids.

• Potassium chloride is used in the preparation of some medications and food additives.

Principle of Work

• In the test for potassium ions experiment, potassium ion in potassium chloride is detected through some identification and confirmatory tests.

• The potassium radical is among the sixth group of basic radicals that are also called the soluble groups.

• This returns back to that all of the members remain soluble throughout most of their identifications tests.

• During the potassium identification test experiment, salt solubility in water will be tested.

• Then confirmatory tests will be carried out which are sodium cobalt nitrite test, perchloric acid, and flame test.

First: Physical Appearance Test:

• In this test, the physical appearance of potassium salt is investigated in terms of color, odor, texture, etc.

Second: Solubility Test:

• In this test, a sample of the potassium chloride salt is tested for its solubility in cold and hot water.

Third: Sodium Cobalt Nitrite Test:

• It depends on the fact that sodium cobalt nitrite will react with potassium chloride as the cobalt nitrite would displace chloride in potassium. This will lead to the formation of potassium cobalt nitrite as a yellow precipitate in this confirmatory test for potassium ion.

KCl + Na3[Co(NO2)6] → 3NaCl + K3[Co(NO2)6] ↓

• The yellow precipitate is not soluble in acetic acid.

Fourth: Perchloric Acid Test:

• It depends on the fact that chlorate ions could displace chloride ions in their salts leading to precipitation of potassium chlorate as a white precipitate.

HClO4+KCl → HCL + KClO4 ↓

Fifth: Flame Test:

• It is also called a dry test as it uses the potassium chloride salt as it is without dissolving it in water. It depends on the fact that potassium chloride can change the non-luminous benzene flame into an ignited purple colored flame during the test for potassium ions.