5.5 Solutions
• Molarity vs. Molality
• Percent concentration
• Acid-base reactions
• Titration
1.1 Key Topics
• A lot of chemistry actually involves solutions…
• Our blood is amazing…
Solutions
• (solution) concentration – amount of solute in
a given amount of solvent
• Dilute solution – small amount of solute
• Concentrated solution – large amount of
solute
• Molarity vs. Molality
– Molarity (M) is defined as the moles of solute per
liter of solution
mol
M=
liter
• Molality (m or molal) on the other hand, is
moles per kilogram of solvent
mol
m=
kg
• Question:
– How many moles of sodium chloride are there in
500 mL of 1 M NaCl?
• Answer:
• Question:
– How many moles of sodium chloride are there in
500 mL of 1 M NaCl?
• Answer: 0.5 moles NaCl
• Question:
– How many grams of sodium hydroxide should be
added to 200 mL of water to make a 0.5 M
solution of NaOH?
• Answer:
• Question:
– How many grams of sodium hydroxide should be
added to 200 mL of water to make a 0.5 M
solution of NaOH?
• Answer: 4 g NaOH
• % concentration
– Could either be expressed as percent by volume
(% v/v) or percent by weight (% w/w)
• Other expressions for concentration include:
– ppm (parts per million)
• Ex. mg/L
– ppb (parts per billion)
• Ex. µg/L
volume of solute
• Percent by volume =
x 100
volume of solution
mass of solute
x 100
• Percent by mass =
mass of solution
• What is the % by mass of NaCl if 25.5 g is
dissolved in 425 mL of water? Assume that the
density of water is 1g/mL.
25.5 𝑔 𝑁𝑎𝐶𝑙
𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑏𝑦 𝑚𝑎𝑠𝑠 =
× 100 = 5.66% 𝑁𝑎𝐶𝑙
25.5 + 425 𝑔 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
Chemistry and the Environment
• The toxic effects of
heavy metals have been
of serious concern for a
long time
• These metals are
usually found in nature
but are also used in
industries such as
mining and energy and
products such as paints
and gasoline
Chemistry and the Environment
• Our exposure to these metals
increase alarmingly over the
years through contaminated
drinking water and food!
• Long term exposure to even
very small amounts of these
metals could lead to some
serious health issues
• ex. Arsenic poisoning usually
manifests in cases of skin
lesions and skin cancer while
mercury and lead are known
to cause acute to severe
neurological damage
especially to children
Chemistry and the Environment
• Measures have been
implemented to help lower
our exposure to heavy metals
• Guidelines have been set on
what constitutes “safe” levels
of these metals in things like
food and water
• Arsenic for example, has a
safety limit of 10 µg/L (10 ppb)
in water (WHO guidelines)
• Efforts have been done also to
lessen our dependence on
heavy metals for various
industries that currently rely
heavily on them
Solutions
• More examples
What is the molarity of a solution in which 333 g
of potassium bicarbonate is dissolved in enough
water to make 10.0 L of solution?
• Converting grams KHCO3 to moles KHCO3
– 333 𝑔 𝐾𝐻𝐶𝑂3 ×
1 𝑚𝑜𝑙 𝐾𝐻𝐶𝑂3
100.1 𝑔 𝐾𝐻𝐶𝑂3
= 3.33 𝑚𝑜𝑙 𝐾𝐻𝐶𝑂3
• Getting the molarity (mol/L)
– 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 =
3.33 𝑚𝑜𝑙 𝐾𝐻𝐶𝑂3
10.0 𝐿 𝑠𝑜𝑙𝑛
= 𝟎. 𝟑𝟑𝟑 𝑴 𝑲𝑯𝑪𝑶𝟑
• What mass in grams of NaCl is required to
prepare 0.500 L of typical over-the-counter
saline solution (0.15 M NaCl)?
• What mass in grams of NaCl is required to
prepare 0.500 L of typical over-the-counter
saline solution (0.15 M NaCl)?
• Answer: 4.4 g NaCl
Practice Problem
Beer is an alcoholic beverage enjoyed by many people around the world. There are many varieties of
beer, from lagers to pale ales to stouts, and even some unusual ones like fruit beers. Regardless of the
style, however, beer is generally made with four basic ingredients: water, malt, yeast, and hops. Hops
are what gives beer its characteristic bitter flavor. In the early days, brewers needed a way to preserve
beer, and found out that adding hops to the brew allowed the beer to stay fresh for longer. It was later
found out that the hops contain a class of chemicals called alpha acids that when incorporated in the
beer (and heated) turns into iso-alpha acids (or isohumulones) which are very effective against
bacteria and give beer its bitter taste.
Bitterness in beer is measured in terms of IBU, or International Bitterness Unit. Formally, IBU is the
concentration (in ppm w/v) of isohumulone in beer (and so the higher the number, the more bitter the
beer). Lagers have an average IBU of 20, while India Pale Ales are stronger, around 60 to 100(!).
One day, a brewmaster decides he wants to formulate a lager beer with an IBU of 20. He makes a 200 L
batch of beer in the course of a month. Assuming complete incorporation and conversion of alpha
acids, how many moles of isohumulone (molar mass: 362.47 g*mol-1) are in 1 bottle of said beer? (a
bottle holds 500 mL) If the brewer used 200 g of Saaz hops in total, what is the concentration (in %
w/w) of iso-alpha acids in the hops?
Isomerization of humulone to cis- and trans-isohumulone
Reactions in Solution
• For reactions that occur in solution,
stoichiometry will still be very similar
• Remember to still use molar relationships
regardless of how the reactants are presented
(pure substance in grams or in solution) 
• Ex. 60.00 mL of 3.000 M HCl reacted with
12.35 g of sodium bicarbonate. How many
grams of carbon dioxide was produced?
• Chemical equation:
HCl(aq) + NaHCO3(s) -> NaCl(aq) + CO2(g) + H2O(l)
• First, the limiting reagent
• Answer: sodium bicarbonate (NaHCO3)
• Then the amount of product: (CO2)
• Answer: 6.468 g CO2 (4 sig figs)
• Ex. Zinc reacting with sulfuric acid gives zinc
sulfate and hydrogen gas. What volume (in
mL) of 3.00 M H2SO4 is needed to react with
10.0 g of zinc?
• Chemical equation:
Zn(s) + H2SO4(aq) -> ZnSO4(aq) + H2(g)
• Solution:
1 𝑚𝑜𝑙 𝑍𝑛 1 𝑚𝑜𝑙 𝐻2 𝑆𝑂4
10.0 𝑔 𝑍𝑛 ×
×
65.4 𝑔 𝑍𝑛
1 𝑚𝑜𝑙 𝑍𝑛
= 0.153 𝑚𝑜𝑙 𝐻2 𝑆𝑂4
1𝐿
0.153 𝑚𝑜𝑙 𝐻2 𝑆𝑂4 ×
3 𝑚𝑜𝑙 𝐻2 𝑆𝑂4
= 0.0510 𝐿 𝑜𝑟 𝟓𝟏. 𝟎 𝒎𝑳 𝑯𝟐 𝑺𝑶𝟒