Chemistry_2015_STPM term 2_Objectives

Which simple convalent molecule has the highest standard enthalpy of atomisation?

• NO

• N₂

• O₂

• O₃

Which of the following has positive values for all of the enthalpy changes?

• ∆H° 1, ∆H° 2, ∆H° 3 and ∆H° 4

• ∆H° 2, ∆H° 3, ∆H° 5 and ∆H° 6

• ∆H° 2, ∆H° 4, ∆H° 5 and ∆H° 7

• ∆H° 3, ∆H° 4, ∆H° 5 and ∆H° 6

MgCl₂ and NaCl are soluble salts. The enthalpies of solution for both salt are − 106 kJ mol^-1 and + 3.9 kJ mol^-1 respectively. What could be deduced from these information?

• Mg²⁺ ion has a higher hydration energy than Na⁺ ion.

• MgCl₂ is more soluble at higher temperature.

• MgCl₂ has a higher lattice energy than NaCl.

• NaCl is more soluble than MgCl₂

The standard reduction potentials of two half - cell are given below.

E°∕V

Fe²⁺ (aq) + e^- ⇌ Fe²⁺ (aq) + 0.77

Co³⁺ (aq) + e^- ⇌ Co²⁺ (aq) + 1.82

Which statement is true about the above data?

• Fe²⁺ ion is less stable than Fe³⁺ ion

• Co³⁺ ion can oxidise Fe²⁺ ion to Fe³⁺ ion

• Co²⁺ ion is a stronger reducing agent than Fe²⁺ ion

• The e. m. f. of the cell constructed from the half - cell is 2.59 V.

At the end of the experiment, 560 cm³ of O₂ was produce at the anode in I, while the mass of the anode in II decreased by 2.75 g. Which statement is true about the experiment?

[ 1 mol gas occupies 24.0 dm³ under normal conditions]

• The amount of current flowing through the circuit is 0.023 F.

• The relative atomic mass of metal M is 58.9.

• The volume of H₂ produce in I is 560 cm³

• The concentration of M (NO₃)₂ increases.

The rusting of iron is an electrochemical proceeded. The half - equations of the rusting of an ion nail are given below.

Cathode : O2 (g) + 2H₂O (l) + 4e^- ⇌ 4OH^- (aq) E° + 0.40 V

Anode : Fe²⁺ (aq) + 2e^- ⇌ Fe (s) E° − 0.44 V

Which is not true about the process?

• It occurs at the anode.

• It involves the formation of

  Fe (OH)₂

• It occurs faster in a solution with higher pH.

• The oxidising agent is O₂ gas.

Which statement explains the difference in the first ionisation energies between beryllium and boron?

• Boron atom has more valence electrons.

• Boron atom has a greater shielding effect.

• Beryllium atom has a more stable electronic configuration.

• The 2p electron in boron atom is a higher energy level than the 2s electron in beryllium atom.

The acid - base properties of oxides are related to their structure and chemical bonding. Which oxide dissolves in water to form an acidic solution?

• MgO

• SiO₂

• SiO₂

• SO₃

Beryllium compounds behave anomalously in the following aspects:

• BeCl2 is acidic in water

• BeO forms [Be(OH)₄]^2- ion in excess alkali

The reason for this behaviour is because beryllium

• is a small ion

• is a Lewis base

• has a high charge density

• has a low electronegatively value

PbCl₄ could be used as source of Cl₂ gas. Which statement is correct about the property of PbCl₄?

• It is polar.

• It is soluble in water.

• It is a reducing agent.

• It is thermally unstable.