Short exam questions 1

Question 1

Explain the difference between covalent* and *dative covalent bonds [2 marks]

Answer 1

1. Covalent bonds form when each atom* participating in the bonding *donate one electron each.
2. In dative covalent bonding one atom* *donates* the *two electrons required instead of each atom donating one each.

Question 2

Alkenes contain a carbon-carbon double bond, which consists of a sigma interaction* and a *pi interaction.

Describe using molecular orbitals, how these interactions are formed, and which is strongest.

[4 marks]

Answer 2

• Sigma bonds form when orbitals that are in line overlap.
• Pi bonds are formed from orbitals that are parallel overlap.
• Electrons in sigma bonds are closer to the nucleus* so have a *stronger nuclear attraction.
• The electrons in pi bonds are delocalised*, and have a *weaker nuclear attraction and require less energy to remove.

Question 3

Hexane and 2,2-dimethylbutane have the same relative molecular mass. Explain why the boiling temperature of hexane (69 °C) is significantly different from that of 2,2-dimethylbutane (49 °C).

[2 marks]

Answer 3

1. 2,2- dimethylbutane branched. Layers of 2,2- dimethylbutane can’t get as close together as layers of hexane.
2. 2,2- dimethylbutane has weaker Van Der Waals than hexane. So requires less energy to evaporate.

Question 4

Explain why the first ionization energy of calcium (590 kJ mol^–1) is greater than that of strontium (550 kJ mol^–1).

[2 marks]

Answer 4

1. Calcium has less electron shells than strontium. The distance between the valence electrons and nucleus in calcium is significantly shorter than that in strontium.
2. Stronger electrostatic attraction between valence electrons and nucleus in calcium.

Question 5

Explain the term ‘functional group’

[3 marks]

Answer 5

1. Atom/ group of atoms that determine chemical properties and reactivity.
2. to the molecule due to the nature of the bonding and electrons
3. Different molecules with the same functional group will undergo similar reactions

Question 5

Two materials react according to the following equation:

A_(s) + B_(aq) ⇢ C_(aq)

State two factors that would decrease the rate of a reaction between a liquid and a solid, other than by changing the reaction temperature.

[2 marks]

Answer 5

1. Decrease surface area of A - results in less successful collisions of molecules.
2. Decrease concentration of B

Question 6

Two materials react according to the following equation:

A_(s) + B_(aq) ⇢ C_(aq)

Explain how these two factors decrease the reaction rate.

Answer 6

1. Decrease surface area of A - results in less successful collisions of molecules.
2. Decrease concentration of B