Carbon and its Compounds

Potassium Nitrate

Potassium nitrate is a chemical compound with the formula \(KNO_3\). It is an ionic salt of potassium ions  \(K^+\) and nitrate ions \(NO_3^-\). It is an alkali metal nitrate. Potassium nitrate known as saltpetre or nitre is a white solid soluble in water. It is formed by fractional crystallization of sodium nitrate and potassium chloride solutions. On heating, it decomposes and gives nitrite and oxygen. Unlike sodium nitrate it is non-deliquescent. Potassium nitrate is the most common desensitizing agent. A concentration of 5%, potassium nitrate in conjunction with sodium or monofluorophosphate fluoride and reduces symptoms within 2 weeks of daily usage.

Potassium Nitrate

Production of Potassium Nitrate

Potassium nitrate is produced by mixing ammonium nitrate and potassium hydroxide.

\(NH_4NO_3 (aq) + KOH (aq) \rightarrow NH_3 (g) + KNO_3 (aq) + H_2O (l)\)

Another way of producing \(KNO_3\) is to combine ammonium nitrate and potassium chloride. It is easily obtained as a sodium-free salt substitute.

\(NH_4NO_3 (aq) + KCl (aq) \rightarrow NH_4Cl (aq) + KNO_3 (aq)\)

Potassium nitrate can also be made by neutralizing nitric acid with potassium hydroxide. This reaction is highly exothermic reaction.

\(KOH (aq) + HNO_3 \rightarrow  KNO_3 (aq) + H_2O (l)\)

On industrial scale potassium nitrate is produced by the double displacement reaction between sodium nitrate and potassium chloride.

\(NaNO_3 (aq) + KCl (aq) \rightarrow NaCl (aq) + KNO_3 (aq)\)

Properties of Potassium Nitrate

  • The molecular weight or molar mass of potassium nitrate is 101.1032 g/mol.
  • The density of potassium nitrate is \(2.109 g/cm^3\).
  • Also, the boiling point and melting point of potassium nitrate is \(400^oC\) and \(334^oC\) respectively.
  • Potassium nitrate is an orthorhombic crystal. It transforms to a trigonal system at \(129^oC\) or \(264^oF\).
  • Potassium nitrate is moderately soluble in water. Its solubility increases with temperature. Potassium nitrate is not very hygroscopic. It absorbs about 0.03% water in 80% relative humidity over 50 days.
  • Potassium nitrate is insoluble in alcohol and is not poisonous. It reacts explosively with reducing agents.

Potassium Nitrate \(KNO_3\) Uses

  • Potassium nitrate is in use as a form of fertilizer. It contains all the macronutrients for plant growth.
  • Potassium nitrate is in use as gunpowder in explosives like bombs, grenades, etc.
  • It is useful in the manufacturing and production of cigarettes
  • It is in use as extensively used in the preservation of hides
  • Potassium nitrate has medicinal applications like a diuretic in medicine
  • It is present in toothpaste to make the teeth less sensitive to pain. It offers protection against the painful sensitivity of the teeth to ice, sun, acids, sweets or touch.
  • Potassium nitrate has a major use in the food industry. It preserves meat against microbial agents

Health Hazards of Potassium Nitrate \(KNO_3\)

  • Potential exposure – Potassium Nitrate is in use in chemical analysis, as a food additive in fertilizers in medications as a vasodilator and also an antidote for cyanide poisoning.
  • Short term exposure – Potassium nitrate can affect when breathed in the body. Its contact can cause eye and skin burns. It can cause coughing with phlegm. Higher exposures of it can cause pulmonary edema. It is a medical emergency that can be delayed for several hours. This can also cause death.
  • Long term exposure – Repeated contact of potassium nitrate to the skin may cause dermatitis, drying and cracking. It may cause lung irritation and can develop bronchitis. There is very less evidence that proves that potassium nitrite can damage the developing fetus.
  • Medical surveillance – If symptoms develop or overexposure is suspected, one must go for a blood test for methemoglobin, Lung function tests and also consider chest X-ray after acute overexposure.

FAQs on Potassium Nitrate

Question 1: What are the dangers of potassium nitrate?

Answer: Contact of potassium nitrate can trigger irritation of the eyes and skin. Intake of potassium nitrate while respiration can irritate the nose and can cause sneezing and coughing in the throat. High concentrations of potassium nitrate may interfere with the blood’s capacity to carry oxygen. It can cause headache, tiredness, dizziness, and blue skin and lips.

Question 2: Is potassium nitrate safe in toothpaste?

Answer: There is confusion between nitrates and nitrites. The FDA states that nitrates used in potassium nitrate are very secure and efficient for anti-sensitive dental products. Also, temporary pain relief is given by delicate toothpaste.

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