Home / AS & A Level Chemistry 2.2 The mole and the Avogadro constant : Exam Style Questions Paper 1

AS & A Level Chemistry 2.2 The mole and the Avogadro constant : Exam Style Questions Paper 1

A Level Chemistry Paper 1 - All Chapters
Question

Which statement about \(_{53}^{131} I\) is correct?

▶️ Answer/Explanation
Solution

Ans: D

For \(_{53}^{131} I\), the number of neutrons = Mass number (131) – Atomic number (53) = 78. A negative ion means the atom gains 1 electron, so the number of electrons = Atomic number (53) + 1 = 54. Thus, the correct statement is D, which states 78 neutrons and 54 electrons.

Question

Which row is correct?

▶️ Answer/Explanation
Solution

Ans: B

The carbon atom in HCN is triple-bonded to nitrogen. This bond consists of one σ bond and two π bonds. A triple bond is linear, giving a bond angle of \(180^\circ\). Therefore, the number of π bonds is 2 and the bond angle is \(180^\circ\), which corresponds to row B.

Question

Which statement about the Cl –N=O molecule is correct?

▶️ Answer/Explanation
Solution

Ans: D

The central nitrogen atom in Cl-N=O has a steric number of 3 (one single bond to Cl and a double bond to O, which counts as one region). This geometry requires \(sp^2\) hybridization. Option A is incorrect as the molecule has two σ bonds (Cl-N and N-O) and one π bond (in N=O). The molecule is bent, not linear, and is polar due to the electronegativity difference and its shape.

Question

A sample of solid ammonium chloride decomposes on heating.

solid ammonium chloride → ammonia gas + hydrogen chloride gas

A total of \(2.4~x~10^{21}\) molecules of gas is formed. 

How many hydrogen atoms are present in the gaseous products?

A \(1.2~x~10^{21}\)     B \(2.4~x~10^{21}\)          C \(4.8~x~10^{21} \)       D \( 9.6~x~10^{21}\)

▶️Answer/Explanation

Ans:C

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