Chapter 15.5 - Water As A Solvent Of Ionic Compounds

Question 1

What is Dissociation?

Answer 1

The process of dissolving a solid ionic compound in water and separating positive and negative ions to form hydrated ions is called Dissociation.

Question 2

What is Ionisation?

Answer 2

Ionic compound dissolving is called IONISATION

Question 3

What is an Ion - Dipole?

Answer 3

The attraction between an ion and a polar molecule (Eg water) is described as an Ion - Dipole attraction

+ ion attracted to O
- ion attracted to H

Question 4

Explain the process of Dissociation of ionic substances

Answer 4

Ionic substances are made up of ions. (Via transfer electron)
When added to water the ionic substance’s (+) ion is attracted to O of water and (-) ion is attracted to H of water = creating ion-dipole attraction

1. Ionic Bonds between ionic compound are broken
   Hydrogen bonds between water molecules are broken
2. Water molecules are in a continuous state of random motion. But due to attraction the Water orientates so that O slightly(-) is facing cations and H+ (slightly +) is facing the anion. OPTIMISING ION-DIPOLE attraction.
3. If the attraction is strong enough the water molecules PULLS the ions on the outer part of crystal out of the lattice and into the surrounding solution.
4. The ions in the lattice will disassociate from each other and become hydrated.

Question 5

How to write the equation?

Answer 5

H2O (l)
NaCL (s) (ionic compound) ➡️➡️➡️ Na+ (aq) + Cl- (aq) ions

• note that the formula of water sits above the arrow due to no direct reaction between the H2O and ionic compound
• no chemical change only change in state (s-l)

Question 6

Difference between dissociation of ionic compounds and ionisation of molecular compounds?

Answer 6

dissociation of ionic compound - simply freeing ions from the lattice so that they can move throughout the solution

ionisation of molecular compounds - new ions are formed by the reaction between the molecule of water

Question 7

Why are some ionic compounds insoluble?

Answer 7

Some ionic compounds do not dissolve in water because the energy required to separate the ions from the lattice is greater than the energy released when the ions are hydrated.

Question 8

Why are some covalent molecular compounds soluble?

Answer 8

The covalent compounds that dissolve do so because they tend to have parts of their molecules that are somewhat polar (a negative side and a positive side) just like water. …

The sugar molecules contain polar O-H bonds. The polar O-H bonds in water attract the sugar molecules into solution