WAEC Chemistry Past Questions & Answers - Page 36

Halide: A binary compound of a halogen with another element or group.

- Crystallization is primarily employed as a separation technique to obtain pure crystals of a substance from an impure mixture.

- Another important application of crystallization is its use to obtain pure salt from seawater.

- Simple syrup crystallizes when enough of the sugar molecules stick to one another that they become insoluble in the water

note; distillation is used to obtain a solvent from a solution.

- The ionization energy of an atom is the amount of energy that is required to remove an electron from a mole of atoms in the gas phase:

- It is possible to remove more electrons from most elements, so this quantity is more precisely known as the first ionization energy, the energy to go from neutral atoms to cations with a 1+ charge.

-  The ionization energy decreases from top to bottom in groups, and increases from left to right across a period. 

-  The boiling and melting points decrease as you move down the group.

Ethanol is an alcohol that is soluble in water. This is because of the hydroxyl group (−OH) in the ethanol that is able to form hydrogen bonds with the water (H2O) molecules.

- Increasing the surface area of a reactant increases the frequency of collisions and increases the reaction rate.

- Chips have a lower surface area compared to powder, so it accounts for the slowest