Displacement and Precipitation Reactions Flashcards
Explain solubility
A solute will dissolve in a solvent if the forces of attraction between the solvent and solute are great enough to overcome the forces of attraction between the solute particles
A solute will not dissolve if the forces of attraction between the solute and solvent are weaker than the forces of attraction between the solute particles.
Once the ions separate they are far too small to see, and we say that it has dissolved.
What is a precipitation reaction?
When two ionic solutions are mixed and an insoluble ionic solid is formed
What are spectator ions?
An ion that does not participate in a reaction.
Why are many ionic compounds soluble in water?
Because the attraction between the slightly charged end of the water molecules and the ions are greater than the attraction between the negative and positive ions.
What is the solubility of an ionic compound affected by?
The amount of water/solute -> saturation
Temp of water
Specific ionic compound.
What happens when an ionic compound dissolves?
The ions are pulled away from the ionic lattice and become separated by water molecules. All solutions of ionic solids contain anions and cations surrounded by water molecules. Ions in solution are known as aqueous ions
eg
NaCl (s) -> Na+(aq) + Cl-(aq)
What is an exchange reaction?
When two solutions of ionic compounds are mixed and ions are exchanged between the reactants to form 2 new compounds
Compound AB + compound CD -> compound AD + compound CB.
Since ions in aq solution are separated from each other, an exchange reaction can be observed only if a precipitate is formed as one of the products.
How to separate the solid precipitate from solution?
Filtration
eg when a precipitation reaction does not happen
A mixture of Na2SO4 and KCl solution does not produce a precipitate. This is because both possible products (K2SO4 and NaCl) are soluble. There is no exchange of ions and, hence, no precipitation reaction occurs.
When writing equations
PUT THE STATES AND AQ ETC to show the precipitate
Regarding spectator ions
The equation Ca(NO3)2 + Na2SO4 -> CaSO4 (s) + 2NaNO3 can be simplified by eliminating any ions that do not change in the reaction.
If writing out all the ions, CaSO4 is still written together because the ions are bonded together.
After cancelling out spectator ions
So it becomes
Ca2+ + SO4(2-) -> CaSO4
Colours
Fe2+ = green Fe3+ = orange Cu2+ = blue
except CuCO3 -> green-blue
CuO = black
Other ions are white
Sulphuric acid is colourless
What is a metal displacement reaction
When a metal ion in a solution is replaced by another type of metal.
element A + compound BC -> element B + compound AC
Eg of metal displacement reaction
The iron nail (solid metal) is placed in a solution of blue copper ions, and colourless sulphate ions. The new products that form are pink Cu atoms (solid copper) and pale-green iron (II) ions, Fe2+ (the iron metal appears to dissolve). The iron atoms form Fe2+ in solution. The copper ions that are in solution form solid copper metal on the surface of the iron. The iron metal displaces the copper ions from the copper sulfate solution.
Uses of reactivity series in life
- silver and gold are very unreactive and good conductors of electricity so commonly used in electronics
- Cu and Pb are quite unreactive and easily bent into shape - commonly used in plumbing
- Sn, less reactive than iron, is used to palte tin cans to protect the iron from rusting
- Zn, more reactive than iron, is used to galvanise iron nails and roofing iron. Because zinc will oxidise more readily than iron, it protects the iron form being oxidised.
