Cette leçon contient 13 diapositives, avec diapositives de texte.
La durée de la leçon est: 45 min
Éléments de cette leçon
Salts and water
How do salts dissolve in water?
Which salts do/ do not dissolve in water?
How do metal oxides react with water?
Precipitation reactions
What are salt hydrates?
Slide 1 - Diapositive
Condensed formula of a salt
Fe2+ and OH-
Fe(OH)2
Do not forget the brackets!
Slide 2 - Diapositive
When a salt goes into water...
Ions are "pinched off" the ionic grid by water molecules, this process is known as hydration
Once an ion is in solution, it is surrounded by a small mantle of water molecules (usually 4-8) and we say it has been dissolved in water
The bond between the water molecules and the ion is called the ion-dipole bond
Whether hydration even occurs - i.e. whether the salt dissolves in water - depends on the relative strength of the ionic bonds compared to the ion-dipole bonds
this determines a salt's solubility (Binas tabel 45A)
Slide 3 - Diapositive
When a salt goes into water...
Binas tabel 45A:
g: Soluble (e.g.: NaNO3)
m: slightly soluble (e.g.: MgSO3)
s: insoluble (e.g.: CaCO3)
r: reacts with water (e.g.: CaO)
i: unstable (e.g. NH4OH)
Slide 4 - Diapositive
Dissolution equations for salts
Do not include water in the reaction!
General form: Solid salt (s) --> dissolved ions (aq)
Multiple ions in the condensed formula means coefficient higher than 1
NaCl(s)→Na+(aq)+Cl−(aq)
CuCl2(s)→Cu2+(aq)+2Cl−(aq)
Slide 5 - Diapositive
Evaporation equations for salts
Simply the reverse of dissolution
General form: dissolved ions (aq) --> solid salt (s)
Na+(aq)+Cl−(aq)→NaCl(s)
Slide 6 - Diapositive
Metal oxides
Some metal oxides (Na2O, K2O, CaO en BaO) react with water
These have an "r" in Binas 45A
For these you DO have to include water in the reaction equation!
Slide 7 - Diapositive
Precipitation reactions
What can happen when you mix 2 salt solutions:
The mixture remains a clear solution; all ions are dissolved
The mixture becomes turbid: 2 of the ionic species react, creating solid particles; a precipitate.
Slide 8 - Diapositive
Binas 45A
Slide 9 - Diapositive
Note: this resembles an evaporation equation!
The reaction then becomes
Slide 10 - Diapositive
Salt hydrates
Water molecules are inserted in the crystal lattices of some special salts. These salts (BEFORE adding water!) are calledhygroscopic.
The absorbed (technically: "intercalated") water inside the crystal structure is called "water of hydration"
Hydration is always exothermic
Slide 11 - Diapositive
Zouthydraten
Examples:
Gypsum
Cement
Slide 12 - Diapositive
Zouthydraten
Nomenclature:
(name of the salt) [centre dot] (no. of watermolecules)
La durée de la leçon est: 45 min
