Ammonium Iodide: Formula, Structure, Sample Question

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Collegedunia Team

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Ammonium iodide (NH4I) is a chemical compound that can be made in a lab by ammonia (NH3) with hydroiodic acid or hydrogen iodide gas (HI). Ammonium iodide is an ionic compound which means both ammonium and iodine have a charge. This compound is used as an ingredient in many drugs and also for photographic chemicals. It is considered harmful to humans when inhaled as it causes skin or eyes irritation but shall not be classified as acutely toxic. The basic property of ammonium chloride is solubility as it is easily soluble in water as well as ethanol. 

Also Read: Iodine

Key terms: Ammonium iodide, chemical compound, ammonia, hydroiodic acid, hydrogen iodide gas


Structure and Formula

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Formula of Ammonium Iodide: NH4I

Structure: 

Structure of Ammonium Iodide

Structure of Ammonium Iodide

Also Read: Ions


Preparation

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  1. When potassium iodide is mixed with ammonium sulphate and kept for cooling. After that, alcohol is added and mixture remains untouched for several hours. The obtained precipitate of potassium sulphate is filtered and ammonium iodide is obtained.

(NH4)2SO4 + 2KI → 2NH4I + K2SO4

  1. When ammonia is reacted with hydroiodic acid or hydrogen iodide gas, it gives the required ammonium iodide.

NH3 + HI → NH4I

  1. When ammonium hydroxide comes in contact with the hydroiodic acid or hydrogen iodide gas then it results in ammonium iodide and water.

NH4OH +HI → NH4I + H2O


Physical Properties of Ammonium iodide

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Ammonium iodide is white in colour and turns yellow colour when it comes in contact with the water or light.

The melting and boiling point of the compound is 551 °C and 405 °C respectively.

Moreover, the density is 2.514 g/cm3.

Ammonium iodide with the compound formula NH4I has a molecular mass of 144 amu. Molecular mass is calculated as the total of the atomic masses of the elements. 

Here, atomic mass of Nitrogen (N) = 14 amu

atomic mass of Hydrogen (H) = 1 amu 

atomic mass of Iodine(N) = 126 amu

So, molecular mass of NH4I = atomic mass of Nitrogen (N) + 4 × atomic mass of Hydrogen (H) + atomic mass of Iodine(N)

Molecular mass of NH4I = 14 + 4×1 + 126 amu

Molecular mass of NH4I = 144 amu

The exact mass of NH4I is 144.938847 amu.

Also Read: Phosphine


Things to Remember

  • Ammonium iodide is an ionic compound.
  • Ammonium iodide is completely soluble in water and ethanol.
  • NH4I is neutral in nature.
  • An aqueous ammonium iodide solution has a pH of 5.50.
  • Ammonium iodide is acid when dissolve in water.
  • It is harmful when inhaled or comes in direct contact with the human body.

Sample Questions

Ques: Does ammonium iodide affect humans? (2 Marks)

Ans: When a person inhales the ammonium iodide, it causes irritation in the nose, throat and eyes.  The toxic and irritating fumes of the hydrogen iodide, iodine, and oxides of nitrogen may result in fire. The compound may sublime into the fire and then condense on the cold surfaces. The ammonium iodide should be kept in a tightly closed and protected container and the sunlight should not enter that container.

Ques: What are the uses of ammonium iodide? (2 Marks)

Ans: Ammonium Iodide is an inorganic compound and is the major component of a compound of the same name, that is used as a fertiliser. It is a radioisotope that is used as a radioisotope tracer for the study of water flow through soils, rocks, and other porous media. Also, ammonium iodide is used in a wide variety of applications, such as glass production, construction, concrete, and more. But in recent years, it's gained more attention for its potential use in the treatment of thyroid disease.

Ques: When ammonium iodide was found? (2 Marks)

Ans: Ammonium Iodide (AI) is a synthetic chemical element that was first discovered in the form of perchlorate in 1785. In 1863, the element was found to be insoluble in water, so it was only used as a component in many types of explosives. It was used as a fertiliser in the late 1800's and was later considered a useful "food additive" due to the element's ability to inhibit iodine uptake in the thyroid gland.

Ques: What happens when ammonium iodide is heated? (2 Marks)

Ans: The melting and boiling point of the ammonium iodide is 551 °C and 405 °C respectively. Solid ammonium iodide decomposes to ammonia and hydrogen gases at sufficiently high temperatures.

NH4I (s) → NH3 (g) + HI (g)

The equilibrium constant for the decomposition at 400 °C is 0.215. Twenty grams of ammonium iodide are sealed in a 0.75-L flask and heated to 405 °C.

Ques: Is ammonium iodide a weak acid? (2 Marks)

Ans: Ammonium iodide is neutral in nature i.e., not acidic nor basic. It is prepared from hydroiodic acid (HI) and ammonia (NH3). Among these hydroiodic acid is a strong acid and ammonia is a weak base that neutralises the resultant product ammonium iodide. The aqueous solution of a salt produced by strong acid and a weak base is acidic in nature

Ques: What happens when ammonium iodide is dissolved in water? (2 Marks)

Ans: Ammonium iodide reversible dissociates into water and behaves acidic in nature due to the formation of ions.

NH4I(s) + H2O (I) → NH4+ (aq) + I- (aq)

It is completely soluble in water. Also, it is easily soluble in ethanol and methanol, acetone and glycerol.

Ques: What kind of bond does ammonium iodide hold? (2 Marks)

Ans: Ammonium iodide is an ionic bond compound as both ammonium and iodine have a charge on them. Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds.

Ques: Where iodine is usually found? (2 Marks)

Ans: Iodine is essential to trace elements that many claim that we need, yet so little of it is actually consumed in our diets. Instead, it is most commonly found in our drinking water and the foods that we eat. However, this is not its only source. Ammonium Iodide is a compound that is used to treat and prevent thyroid conditions. Ammonium Iodide is commonly found in household products like deodorants, etc.

Ques: Is ammonium iodide safe to use in drugs? (2 Marks)

Ans: As a drug that is no longer used by the medical community, the safety of use of Ammonium Iodide has become a topic of much discussion. There is a lot of misinformation out there, and people are just looking for a reason to dismiss it. The facts are simple, and the results of tests have shown Ammonium Iodide to be extremely safe when used under the right circumstances.

Ques: Is ammonium iodide a solid or gas? (2 Marks)

Ans: The ammonium iodide is visible in the form of a white crystalline powder. In addition, it has a melting point of 551 °C whereas it has a boiling point of 405 °C. Its molar mass is 144.94 amu with a density of 2.51 g/cm3.

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