Intro to Stoichiometry Flashcards
What is a solution?
Solutions are homogeneous mixtures of substances composed of at least one solute and one solvent
Liquid-state and gas-state solutions are clear (transparent) – you can see through them; they are not cloudy or murky in appearance!
Both solutes and solvents may be gases, liquids, or solids, producing a number of different combinations
Classification of Solutions
gas in gas
oxygen in nitrogen (air)
gas in liquid
carbon dioxide in water (soft drinks)
gas in solid
oxygen in ice
liquid in gas
water in air (humidity)
liquid in liquid
ethanol in water (alcoholic beverages) amalgram
liquid in solid
mercury in silver (old tooth fillings)
solid in liquid
sugar in water (soft drinks) Alloy
solid in solid
tin in copper (bronze)
Aqueous Solutions
A solution in which water is the solvent
“mixed in water”
Most important type of solution in chemistry!
Solutes in aqueous solution are either ionic compounds or polar molecules
The dissolving of ionic compounds in water
As the ions leave the crystal form, they become surrounded by a sphere of water molecules – this is called hydration
The dissolving of ionic compounds in water
The process in which ions separate from ionic crystals, becoming individual ions, is called dissociation
We can write dissociation equations:
NaCl(s) –> Na+(aq) + Cl - (aq)
These equations are NOT showing a reaction
The dissolving of molecular compounds in water
Molecular compounds must be polar in order to dissolve in water
Hydrogen bonding between ethanol and water molecules allows these liquids to form a solution.
“Like dissolves like” principle
Ethanol is miscible in water
What about non-polar molecular compounds?
These cannot dissolve in water, as they lack full charges or dipoles
However, non-polar molecules can dissolve in non-polar solvents
They do this via interaction of weak, temporary dipoles – London Dispersion forces
Surfactants
These are special molecules that encourage polar and non-polar molecules to mix
They have both a polar and a non-polar part
Surfactants in soap
Polar (hydrophilic) end
non-polar (hydrophobic) end
the cation head is usually Na+
