LEARNING OBJECTIVES:
1) Know how to safely mix a solution to the proper concentration from both a solid and a liquid.
2) Be able to calculate different units of concentration (e.g. molarity (M), molality (m), percentage (%) and normality (N).
3) Correctly apply the terms (concentrated vs dilute) and (strong vs weak) as they apply to solutions.
4) Know which pieces of glassware would be used and how to correctly read volumes when making solutions.
Compare Molarity (M = mol/L) vs. molality (m = mol/kg).
we use molarity in labs:
industry uses molality.
Look at at discuss glassware:
Beaker (hold a substance) Erlenmeyer flask (mix a substance by swirling) Volumetric flask (mix a solution with high precision) Graduated cylinder (measure liquids to be poured into a beaker or erlenmeyer flask)
Erlenmeyer flask 1000 mL (+/-) 5%
when filled holds between 950 mL - 1050 mL
Volumetric flask 1000 mL (+/-) .40 mL
when filled holds between 999.6 mL - 1000.4 mL.
Go through "How to make a standard 'molar' solution".
How would you mix 750 mL of 0.5 M
CuSO4x5H2O?
Go through steps: Wearing proper safety equipment (i.e., safety glasses,
gloves)
a) calculate moles of copper sulfate pentahydrate required (use M = mol / L)
b) calculate the mass equivalence of number of moles calculated
in step (a)
c) Fill a *750 mL volumetric flask with ~500 mL of distilled water THEN add measured amount
of copper sulfate pentahydrate
using a powder funnel. [Adding water to concentrated acid
is dangerous!]
Always add acid to water (not water to acid). The acid will spatter like
getting water in hot oil.
d) Rinse neck of flask and funnel with distilled water. Swirl flask to dissolve salt.
e) Bring final volume to 750 mL.
*750 mL volumetric flasks don't exist! You would either need to mix 500 mL + 250 mL or recalculate amount for 1000 mL and mix extra solution.
Explain the difference between strong vs. weak acids and concentrated vs.
dilute acids.
Strong
HA --> H+ + A- (dissociates ~100%)
Weak
HA <==> H+ + A- (dissociates > 20%)
Concentrated (lots of solute)
vs. Dilute (little solute)
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