Cobalt chloride solution

The importance of solutions

1- They're essential for the biological processes inside living organisms

2- They're important for the occurrence of some chemical reactions

 The substances forming solutions are regularly distributed in all the solution parts

True solution: A homogenous mixture of two or more substances

The substance which exists in greater amount in solutions are called" solvents", while substances that exist in smaller amounts and dissolve in solvents are called "solutes"

Solutions are classified according to the physical state of both solute and solvent

Examples	Solute type	Solvent type	Solution type
Air - Natural gas-	gas	gas	gas
-Water vapour in air - gasoline mixture in air	liquid	gas	gas
Naphthalene in air	solid	gas	gas
- Dissolved oxygen in water - Fizzy drinks	gas	liquid	liquid
- Alcohol in water - ethylene glycol(anti-freezing) in water	liquid	liquid	liquid
- salt of sugar in water	solid	liquid	liquid
-Hydrogen in palladium and platinium	gas	solid	Solid
- silver amalgam Ag(s) / Hg(l)	liquid	solid	Solid
- alloys (Nickel-chrome alloy)	solid	solid	Solid

Some important concepts

Electronegativity: The ability of atom to attract electrons

Polar bond: A type of covalent bond between two atoms in which electrons are shared unequally (the greater atom carries a negative charge)

Polar molecule: A Molecule which has a bond carrying molecular positive charge and another one carrying molecular negative charge

The bonds in water molecules are polar because the negative charge (electronegativity) of oxygen is greater than that of hydrogen. Thus, oxygen atom carries molecular negative charge, while hydrogen atoms carry molecular positive charges.

 The angle between the two bond of water molecule equals 104.5◦

Design of water molecule (the angle between the two bonds = 104.5◦)

Electrolyte and non electrolyte solutions

Electrolytes: Substances whose solutions can conduct electric current via the movement of free ions

Electrolytes are divided into:-

Strong Electrolytes: Electrolytes that completely disassociate in water (all their molecules disassociate into ions) which makes them high conductors of electricity

Examples:-

 Ionic compounds: sodium chloride (NaCl) and sodium hydroxide (NaOH)

 Polar covalent compounds: Hydrochloric acid (HCl) (it conducts electricity if it's a solution, not in gaseous state)

When hydrochloric acid dissolves in water, positive hydrogen ions are produced and bond with water molecules forming hydronium (H3O+)

HCl (g) + H2O (l)  H3O+ (aq) + Cl- (aq)

Weak Electrolytes: Electrolytes that partially disassociate in water (small no. of its molecules disassociate in water) which makes them low conductors of electricity

Examples:-

 Acetic acid CH3COOH (vinegar)

 Ammonium hydroxide (ammonia solution) NH4OH

 Water H2O

Non electrolytes: Substances whose solutions cannot conduct electricity because of the absence of free ions

Examples on non electrolytes:-

 Sugar

 Ethyl alcohol (ethanol)

Dissolution process: The process in which the solute molecules disassociate into negative ions, positive ions, or separated polar molecules and then get surrounded by the molecules of solvent

Polar and ionic compounds dissolve easily in water, while non polar molecules (fats, oil, methane…etc) don't dissolve in water (but dissolve in

benzene).

To know how dissolution process occur, we should know that water molecules are in continuous motion due to their kinetic energy

When putting an ionic compound crystal (such as NaCl) in water, water molecules collide with the crystal and attract its ions. This process is the dissolution process

 A true solution is composed of regularly-distributed ions or molecules whose diameters range from 0.01 nm to 1 nm. This makes the solution homogenous and allows light to penetrate it

 When putting little sugar in water, the polar molecules of sugar gets separated and bond to those of water by hydrogen bond forming sugar solution