STPM SEM 1 quiz 2

²⁸ ₁₄ Si and  ³⁰ ₁₄ Si are two isotopes of silicon. The relative atomic mass of Si is 28.1. Which statement is true about these isotopes?

•  ²⁸ ₁₄ Si is smaller than ³⁰ ₁₄ Si.

• ²⁸ ₁₄ Si and ³⁰ ₁₄ Si are radioactive .

• ²⁸ ₁₄ Si is more abundant than ³⁰ ₁₄ Si.

• The total number of sub-atomic particles in ²⁸ ₁₄ Si and ³⁰ ₁₄ Si is the same.

The mass spectrum of an element is shown in the picture.

Which statement is true about the element?

• The element has two isotopes.

• Peak X is due to a dipositive ion.

• The element is a diatomic molecule.

• The relative atomic mass of the element is 38.

Lithium oxide is used to remove water vapour and carbon dioxide exhaled by astronouts aboard a space shuttle. The chemical equation for the reactions involved are shown below.

Li₂O(s) + H₂O(g) →2LiOH(s)

LiOH(s) + CO₂(g) →LiHCO₃(s)

If 50.0 kg of lithium oxide is available, what is the maximum number of carbon dioxide molecules which can be removed?

[Relative atomic mass of H,Li,C and O are 1.0, 6.9, 12.0 and 16.0 respectively; Avogadro constant is 6.02 x10²³ mol^-1]

• 1.01 x 10²⁴

• 2.02 x 10²⁴

• 1.01 x 10²⁷

• 2.02 x 10²⁷

The lines in the Lyman series of an emission spectrum of a hydrogen atom is shown below. Which line represents an electronic transition with the smallest energy change?

• p

• q

• r

• s

Which statement is not true about s, p and d orbitals?

• Three 2p orbitals have the same shape and energy.

• The size of 1s orbital is smaller than that of 2p orbitals.

• 2s orbital is non-directional whereas 2p_x orbital is directional.

• Vacant 3d orbitals are at a lower energy level than a vacant 4s orbital.

Which statement about lewis structure of CO₃^2-  and NO₃^- ions is true?

• Both ions are trigonal planar in shape.

• Both ions have a formal charge on the central atom.

• Both ions form two double bonds and one single bond.

• Both ions have central atom with one pair of unpaired electron.

 The phase diagram of substance X is as given.

Which statement about the phase diagram is true?

• Substance X exists as a solid at stp.

• Solid X sublimes at temperature below its triple point.

• The freezing point of liquid X decreases as pressure increases.

• Substance X exists as a supercritical fluid at temperature above 31.1°C.

Which graph represents Charles’ law for a fixed mass of a gas?

• 
• 
• 
• 

The diagram shows the bond angle of water and hydrogen sulphide.

The bond angle of water is greater than hydrogen sulphide because

• Oxygen atom is more electronegative than sulphur.

• Sulphur atom is more electronegative than oxygen.

• The force of repulsion between two S-H bonds is greater compares to the O-H bonds.

• The oxygen atom is larger than the sulphur atom.

Which statement about the collison theory is true?

• A catalyst lowers the activation energy of a reaction.

• An activated complex is formed when molecules collide.

• The frequent of collision is proportional to the concentration of reactants and products.

• An effective collision involves reactants with the certain minimum energy and the correct orientation of particles.