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Solutions
Solutions
• A solution is a homogeneous mixture
where all particles exist as individual
molecules or ions.
• Mixtures in chemistry are combinations of
different substances where each
substance retains its chemical properties.
A solution is a homogeneous mixture.
• Homogeneous means that the mixture is
the same all the way through.
• You could take two same-sized samples:
one from the bottom and one from the top
and they would be identical.
• Homogeneous mixtures do not settle out
if left to sit undisturbed.
A solution has two components:
the solute and the solvent.
• The solvent is the substance in greater
amount. It does the dissolving.
• It is usually a liquid, but it doesn’t have to
be. (It is usually water)
• The solute is the substance in lesser
amount. It get dissolved.
• It is usually a solid, but it doesn’t have to
be.
Like dissolves Like
• A polar solute dissolves in a polar solvent.
• A non-polar solute dissolves in a nonpolar solvent.
• Other chemical properties also decide
whether a solute will dissolve or not.
Saturation
• Saturated solution: contains the maximum
amount of solute in a solvent.
• Unsaturated solution: contains less than
the maximum amount of solute in a
solution.
• Supersaturated solution: contains more
than the maximum amount of solute in a
solvent (this occurs when a solution is
heated, solute added, then gradually
cooled).
Factors affecting Solubility
PRESSURE
: only gases can be affected by
pressure.
TEMPERATURE
: gaseous solutes require a cooler
temperatures to increase solubility.
: liquid and solid solute will dissolve
more readily in hot solvents.
Factors affecting rate of dissolving
• Heating
• Stirring or Shaking
• Increasing surface area
• These processes all increase the
number of interactions between
solute and solvent.
The word concentration refers to
how much solute is dissolved.
• It is a quantity.
• Dilute means that only a little solute is
dissolved in a lot of solvent(20.0g or less per
100ml solvent).
• Concentrated means a great deal of solute is
dissolved in a little solvent(20.0g or more per
100ml of solvent).
• For example, 100.0g HCl in a little water is
concentrated, while 100.0g HCl in a lot of
water is dilute.
Molarity measures concentration.
Molarity = moles of solute
litres of solution
Ex: What is the Molarity of 53.5grams of calcium
chloride dissolved in 362ml of solution?
• Change grams of solute to moles of solute.
• Divide moles of solute by litres of solvent.
1 mole CaCl2 = 111.0g CaCl2
x
53.5g CaCl2
x = 0.482 mol CaCl2
Molarity = moles of solute
litres of solute
M = 0.482 moles
0.362 litres
M = 1.33M
Suppose you had 58.44 grams of NaCl and you
dissolved it in exactly 2.00 L of solution.
What would be the molarity of the solution?
58.44g is 1 .000 moles of NaCl
Molarity = moles of solute
litres of solution
M = 1.000 mol
2.00 L
M = 0.500 M
How many litres is needed to prepare a
0.876M solution of potassium nitrate that
contains 12.0g of solute?
1 mole KNO3 = 101.1g
x = 0.119 mol
x
12.0g
M = Moles
Litres
0.876M = 0.119 moles
x litres
x = 0.136 litres
(or 136ml or 136 cm3)