Solutions
Solid in a Liquid
What we want to do is start with a solid and a liquid, and just end up with a
homogenous mixture.
Concentration
Knowing how many moles are in your solution.
Finding Mass
Mass = moles x molar mass
= n x MM
m
n MM
If I want a concentration of
have 0.036M of CaCl2 what is
the mass of the powder?
+
mass = (moles of CaCl2) x (Molar Mass of CaCl2)
=
nxM
So how do we get to this point?
Concentration
n
= required concentration
Total Volume of solution
=
C
V
=
0.036M
0.500L
=
0.0180mol
m=
=
=
(moles of CaCl2) x (Molar Mass of CaCl2)
0.0180 mol x 110.97g/mol
1.99g
Therefore you would have to add 1.99g of CaCl2 to
0.500L to get a concentration of 0.036M.
Process of making a
solution from a solid
• Get a 500 mL Volumetric Flask
• Place it on a mass balance and tare the balance
(zero it).
• Mass out 1.99 g of solute (CaCl2)
• Fill the flask up, almost to the top and dissolve the
solute.
• Top up with distilled water to the calibration mark
and stopper it.
Liquid into a Liquid
Here when we talk about adding a liquid to a liquid to make a solution
we talk about diluting the concentration.
Same amount of
moles of the
solute, just
spread out over a
greater volume.
Increase Volume you decrease Concentration
The reason being is that the two are inversely proportional
If we increase the amount of moles added, what happens to the concentration?
• If we change the volume and the concentration
but keep the moles constant, we can use a second
equation
C1V1 = C2V2
Where C1 would represent the concentration before
dilution.
Where C2 would represent the concentration after
dilution.
If we have 0.5M of ethanol
how much do we add to
100mL to get 0.35M
C1V1 = C2V2
(0.5M)V1 = (0.35M)(0.100L)
V1 =(0.35M)(0.100L)
0.5M
V1 = 0.070L
Therefore you would want to add 70mL of ethanol to 30 mL
of distilled water to get a concentration of 0.35M
Process of adding Liquids
to Liquids
• Get a 0.500 L Volumetric Flask
• Measure 70 mL of concentrated ethanol (if it is a
stronger acid/base add using gloves, apron, shield)
• Half fill the 0.500 L Volumetric flask with distilled
water
• Add the 70 mL of concentrated HCl
• Top up with distilled water to the calibration mark.