Chapter 15.4 - Water as a solvent of ionic compounds

Question 1

What molecular compounds can dissolve in water?

Answer 1

Molecular compounds which form HYDROGEN BONDS are often soluble in water.

This is because the strength of the intermolecular forces between the solute and the solvent are similar - the 2 substances can readily interact with each other

Question 2

What are some polar compounds which form hydrogen bonds with water?

Answer 2

Sugars - fructose, glucose, sucrose

They dissolve in water by forming hydrogen bonds

Question 3

Do Non polar or Polar molecules dissolve in water?

Answer 3

POLAR molecules dissolve in water

The more polar = the more likely the compound is to dissolve in water

NON POLAR DON’T - because the substances do not have charged ends so no significant attraction to water molecules.
The force of attraction that exists between non polar substances and water are WEAK DISPERSION FORCES which are not strong enough to overcome the relatively strong H bonds between water molecules.

Question 4

Molecular compounds ionise?

Answer 4

Some compounds have molecules with one or more covalent bonds that are so POLAR they break when the compound is placed in water. Eg HCL

Question 5

What do highly polar molecules form when dissolved in water?

Answer 5

Highly polar molecular compounds will form IONs when dissolved in water.

Question 6

What is hydronium ion?

Answer 6

When the Hydrogen ion (H+) from a molecular compound bonds to the water molecule, it forms a new ion - Hydronium ion
Eg H3O+

Question 7

In summary what happens when Hydrogen chloride dissolves in water?

Answer 7

1. Polar covalent bonds within hydrogen chloride molecules break, producing hydrogen ions (H+) and chloride ions
2. A covalent bond forms between the H+ and H2O molecule, forming H3O+

3.ION - DIPOLE attractions form between the H3O+ and Cl- ions and polar water molecules.
Equation - HCl - H2O ➡️H3CO+(aq) + Cl- (aq)

Question 8

What are some other polar molecular compounds which ionise ?

Answer 8

Nitric Acid (HNO3) 
Sulphuric Acid (H2SO4) 
Ethanoic Acid (CH3COOH) 

Ammonia (NH3)

• can dissolve by either forming hydrogen bonds with water
• or by reacting to form ammonium ion (NH4+)

Question 9

How Can Highly Polar molecules form IONS when they dissolve in water?

Answer 9

Eg HCL
Covalent compounds = no ions present but can form ions when dissolved (ionisation)

H+ is formed = Hydronium ion is formed Eg H2O+