This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Ammonia”.
1. What is the chemical formula of ammonia?
Explanation: Ammonia is a tri-hydride of nitrogen. It is a colorless gas with a highly pungent smell that causes nasal irritation. It is the most stable hydride of any element in group 15.
2. What kind of smell is ammonia recognized by?
Explanation: Ammonia has a highly pungent smell. With a sharp, pinching smell, it causes severe irritation in the nose and throat. This pungent smell of ammonia is used as a means to identify the presence of ammonium cation, NH4+ in salt analysis.
3. How many unshared pair of electrons does an ammonia molecule have?
Explanation: The nitrogen atom in NH3 (ammonia) bears one lone pair of electron. Each single electron of hydrogen is bonded to the nitrogen atom. Three of out five electrons of nitrogen are involved in bonding whereas the unbounded two electrons make up the single unshared pair of electron.
4. What happens when sodium is put in a solution of ammonia?
a) It generates a lot of heat
b) It does not dissolve
c) It produces deep blue color
d) Ammonia liquid evaporates due to heat
Explanation: When sodium is introduced to liquid ammonia, it separates into sodium ion and a single electron (Na → Na+ + e–). The single electron produces the deep blue color due to solvation effect producing e–[NH3]n.
5. What is one method of qualitatively analyzing a given salt for presence of ammonia?
a) Solution turns blue litmus red
b) Heating the salt causing decrepitation
c) Using a reagent to obtain dirty brown precipitate
d) Addition of NaOH causing white gelatinous precipitate
Explanation: Typically, Nessler’s reagent is used to test for ammonia. Nessler’s reagent is an alkaline solution of potassium tetraiodomercurate (II). When it combines with ammonia it gives dirty brown precipitate due to the formation of [OHg2.NH2]I. Another method is to add a strong base and heat the mixture. The gas given off is pungent and turns red litmus blue.
6. What is the most acidic of all?
d) Alkaline KMnO4
Explanation: In the listed options, except ammonia, every other compound is a strong base which automatically makes ammonia the most acidic relative to the mentioned compounds. Although it is a weak base, compared to NaOH, KOH and alkaline KMnO4 it is the most acidic amongst the four options.
7. In the Haber-Bosch process, what is formed by the reaction of natural gas and steam?
Explanation: The reaction of natural gas and steam is known as the steam reformation of methane. It is an utmost important step in the Bosch-Haber (industrial process to produce ammonia), which produces hydrogen gas, H2, one of the two reactants alongside nitrogen to produce ammonia in presence of iron catalyst.
8. Which of the following conditions would improve the yield of ammonia production from Bosch-Haber process?
a) High temperature, high pressure
b) High temperature, low pressure
c) Low temperature, low pressure
d) Low temperature, high pressure
Explanation: Following the Le Chatelier’s principle, since the forward reaction is exothermic (i.e. N2 + 3H2 → 2NH3), low temperatures would increase the rate of reaction in turn producing more ammonia. In addition to this, since the total number of molecules on the product side lesser, high pressures will increase the rate of reaction.
9. Nitrogen in plants is taken in what form?
Explanation: Plants take up nitrogen predominantly in the form of nitrate ions, along side ammonium ions. This is made available to them through fertilizers, whose typical examples usually include Ammonium Phosphate, calcium ammonium nitrate.
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