Three statements about ammonia molecules and ammonium ions are given.
1. In aqueous solution, ammonia molecules form coordinate bonds with hydroxide ions.
2. Ammonium ions are Brønsted–Lowry acids.
3. The H–N–H bond angle is larger in the ammonium ion than in the ammonia molecule.
Which statements are correct?
▶️ Answer/Explanation
Ans: C
Statement 1: Incorrect. Ammonia (\(NH_3\)) forms coordinate bonds with \(H^+\) ions (protons) to form ammonium ions (\(NH_4^+\)), not hydroxide ions (\(OH^-\)).
Statement 2: Correct. Ammonium ions (\(NH_4^+\)) can donate a proton (\(H^+\)), making them Brønsted–Lowry acids.
Statement 3: Correct. The \(H-N-H\) bond angle in \(NH_4^+\) (≈109.5°, tetrahedral) is larger than in \(NH_3\) (≈107°, trigonal pyramidal) due to the absence of a lone pair in \(NH_4^+\).
Thus, only statements 2 and 3 are correct, making C the correct answer.
Three statements about ammonia molecules and ammonium ions are given.
1. In aqueous solution, ammonia molecules form coordinate bonds with hydroxide ions.
2. Ammonium ions are Brønsted–Lowry acids.
3. The H–N–H bond angle is larger in the ammonium ion than in the ammonia molecule.
Which statements are correct?
▶️ Answer/Explanation
Ans: C
Analysis of each statement:
1. False: Ammonia (NH3) forms coordinate bonds with H+ ions to form NH4+, not with hydroxide ions (OH–).
2. True: NH4+ can donate a proton (H+), making it a Brønsted-Lowry acid.
3. True: NH3 has a trigonal pyramidal shape (bond angle ≈ 107°), while NH4+ is tetrahedral (bond angle ≈ 109.5°), making the angle larger in the ion.
Therefore, only statements 2 and 3 are correct.
The formula shows the repeat unit of an addition polymer.
–CH(CH₃)CH(CH₂CH₃)–
What is the correct name of the monomer from which this polymer is made?
▶️ Answer/Explanation
Ans: C
To find the monomer:
- Identify the repeat unit: –CH(CH₃)CH(CH₂CH₃)–.
- Reconstruct the monomer by breaking the C–C single bond and forming a C=C double bond between the same carbons.
- This gives the monomer: CH₃–CH=CH–CH₂–CH₃ (pent-2-ene).
Option A uses incorrect IUPAC nomenclature, B is structurally incorrect, and D (pent-1-ene) would produce a different repeat unit. Thus, the correct answer is C (pent-2-ene).
Propanoic acid is treated with reagent X at room temperature. The organic product of the reaction is sodium propanoate. No gas is produced during the reaction.
What could be reagent X?
▶️ Answer/Explanation
Ans: B
Propanoic acid reacts with NaOH to form sodium propanoate and water. No gas is produced. NaHCO3 and Na2CO3 would produce CO2 gas, and Na2SO4 does not react with the acid. Therefore, the correct reagent is NaOH(aq).