Chapter 10_Group 2

which of the following physical properties decreases when going down Group 2?

• Atomic radius

• Number of electron shells

• Number of valence electrons

• First ionisation energy

Which of the following causes the ionisation energy to decrease when going down Group 2?

(I) Increase in shielding effect

(II) Increase in atomic radius

(III) Increase in nuclear charge

• II only

• I and II only

• II and III only

• I, II and III

The standard reduction electrode potentials of several Group 2 elements are as shown.

Which of the following cannot be deduced from the above information?

• Only beryllium can form complex ions.

• Barium is the strongest reducing agent.

• The reactivity of the metals increases down the group.

• The metals become more increasingly electropositive.

Answer explanation

The values of the standard reduction electrode potential indicate the relative reactivity of the elements.

The melting point of Group 2 elements is higher than the melting point of the corresponding Group 1 elements because he Group 2 elements

• have a larger atomic radius

• have higher ionisation energies

• have a more compact metallic crystal lattice

• uses two valence electrons for metallic bond

P, Q and R are three elements of Group 2. The following are the properties of these elements.

P does not react with cold water but can reduce steam

Q dissolves rapidly in cold water, producing an alkaline solution

R cannot react with cold water or steam

Which of the following shows the correct order of increasing proton number of the elements?

• Q, R, P

• R, P, Q

• P, Q, R

• R, Q, P

Answer explanation

P is magnesium

Q could be calcium, strontium or barium

R is beryllium

Which of the following statements best explains why the Group 2 carbonates becomes increasingly less stable towards heat when going up the group?

• The polarisation power of the metal cation towards the carbonate anion increases.

• The ionic bond in the carbonate compounds become increasingly weaker.

• The metals become increasingly electropositive.

• The radius of metal cation decreases.

When 4.80 g magnesium nitrate sample was heated strongly, the final mass of the residue is 1.00 g. What is the percentage purity of the sample?

[Relative atomic mass: N=14.0; O=16.0; Mg=24.0]

• 77.1%

• 81.4%

• 86.8%

• 92.5%

Answer explanation

2 Mg(NO3)2 --> 2 MgO + 4NO2 + O2

Mol of MgO (residue)

Mass of Mg(NO3)2

Percentage purity

When heated, magnesium nitrate decomposes at around 350^oC, whereas barium nitrate decomposes at temperature above 590^oC.

Which of the following does not explain why magnesium nitrate decomposes at lower temperature than barium nitrate?

• Mg²⁺ has higher charge density

• The polarising power of Mg²⁺ ion is stronger

• Magnesium oxide is more stable than barium oxide

• Magnesium nitrate has higher lattice energy

The table shows the lattice energy and hydration enthalpy of three Group 2 sulphates.

Which of the following shows the correct arrangement of the sulphates in order of decreasing solubility?

• P, R, Q

• Q, P, R

• Q, R, P

• R, Q, P

Answer explanation

Compounds whose hydration energy is more exothermic than its lattice energy are more soluble in water.

The following diagram shows the enthalpy changes when magnesium chloride is dissolved in water.

Which of the following are the correct energies for X, Y and Z?

• X: Lattice

  Y: Hydration

  Z: Solution

• X: Solution

  Y: Hydration

  Z: Lattice

• X: Hydration

  Y: Lattice

  Z: Solution

• X: Lattice

  Y: Solution

  Z: hydration

Answer explanation

Lattice energy: heat released when one more of ionic compound is formed from its gaseous ions.

Hydration energy: heat released when one mole of the gaseous ion is completely hydrated in water.

Solution = -LE + Hydration energy