CHEMISTRY 30 – UNIT 2 – SOLUBILITY
MOLARITY
REVIEW
CONCENTRATION
• “CONCENTRATION” CAN BE MEASURED IN A
VARIETY OF WAYS. BY FAR THE MOST USEFUL IS
MOLARITY.
• THE MOLARITY OF A SOLUTION IS CALCULATED BY
TAKING THE MOLES OF SOLUTE AND DIVIDING BY
THE LITRES OF SOLUTION.
MOLARITY
𝑴𝒐𝒍𝒆𝒔 𝒐𝒇 𝑺𝒐𝒍𝒖𝒕𝒆
𝑴𝒐𝒍𝒂𝒓𝒊𝒕𝒚 =
𝑳𝒊𝒕𝒓𝒆𝒔 𝒐𝒇 𝑺𝒐𝒍𝒗𝒆𝒏𝒕
UNITS:
o MOLARITY = MOLAR (M)
o MOLES OF SOLUTE = MOLES (mol)
o LITERS OF SOLUTION = LITERS (L)
EXAMPLE #1
• Suppose we had 1.00 mole of sucrose (about 342.3g) and
proceeded to mix it into some water. It would dissolve and
make sugar water. We keep adding water, dissolving and
stirring until all the solid was gone. We then made sure
that when everything was well-mixed, there was exactly
1.00 liter of solution.
• What would be the molarity of this solution?
EXAMPLE #1
• Molarity = 1.00 mol
1.00 L
• The answer is 1.00 mol/L. Notice that both the
units of mol and L remain. Neither cancels.
• A replacement for mol/L is often used. It is a
capital M. So if you write 1.00 M for the answer,
then that is correct.
EXAMPLE # 2
• Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution.
What's the molarity?
• Molarity = 2.00 mol
1.00L
• The answer is 2.00 M.
• Notice that no mention of a specific substance is mentioned at all. The
molarity would be the same. It doesn't matter if it is sucrose, sodium
chloride or any other substance. One mole of anything contains 6.02 x 1023
units.
EXAMPLE # 3
• What is the molarity when 0.750 mol is dissolved in 2.50 L
of solution?
EXAMPLE # 4
• We can calculate the molarity of a solution when given the amount of
solute in grams. We convert from grams to moles, and then proceed as
in the previous examples.
• What is the molarity of a 2.00L solution that has 102.44g NaCl
dissolved in it?
EXAMPLE #5
• Example #5 – How many grams of NaOH are contained
in 1.45 L of a 2.25 M solution?
EXAMPLE # 6
• What volume (in mL) of a 0.20 M solution of NaOH contains
1.00g of NaOH?
A (SEEMINGLY) COMPLICATED
PROBLEM:
• Example #7 – A 0.050M solution of glycerine, C3H8O3,
and a 0.050M solution of lycine, C5H11NO2, are prepared.
Which solution contains the most dissolved molecules
per litre?
STOICHIOMETRY WITH SOLUTIONS
• Example #8 – How many grams of copper will react to
completely replace silver from 208 mL of 0.100 M solution
of silver nitrate, AgNO3? Your product will be copper (II)
nitrate.
• Use the same stoichiometry steps as always:
• 1. Get a balanced chemical equation
• 2. Take your info and get to moles
• 3. Use the mole ratios to rebalance the equation
• 4. Go where the question asks