CP Chemistry
Ms. Morrison
MOLARITY AND MOLALITY NOTES
Concentration
 definition: the measure of how much solute
is dissolved in a specific amount of solvent
 can be dilute to concentrated
 can use specific numerical quantities to
measure concentration
 molarity
 molality
Molarity
 concentration expressed as the number of
moles of solute per liter of solution
 use M, molar
 ex. 2.5 M solution is a 2.5 molar solution
 Conversion reminder: to convert mL to L,
must divide by 1000 (1000 mL = 1 L)
Molarity Equations
 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 =
 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 =
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒
𝐿𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
# 𝑜𝑓 𝑔𝑟𝑎𝑚𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
𝐿𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
Molarity Example Problem #1
What is the molarity of a solution containing
158 grams of sodium chloride, NaCl, in 2.5 liters
of water?
Molarity Example Problem #2
Calculate the molarity of 250 mL solution
containing 75 grams of H2SO4.
Molarity Example Problem #3
How many grams of NaCl would be dissolved in
1.75 L of a 0.85 M solution of NaCl?
Molality
 concentration expressed as the number of
moles of solute dissolved in 1 kilogram of
solvent
 volume can change with temperature but
mass does not so molarity can change if
temperature changes but not molality
 use m, Molal
 ex. 1.3 m solution is a 1.3 molal solution
 Conversion reminder: to convert g to kg must
divide by 1000 (1000 g = 1 kg)
Molality Equations
 𝑀𝑜𝑙𝑎𝑙𝑖𝑡𝑦 =
 𝑀𝑜𝑙𝑎𝑙𝑖𝑡𝑦 =
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒
𝑘𝑔 𝑜𝑓 𝑠𝑜𝑙𝑣𝑒𝑛𝑡
# 𝑜𝑓 𝑔𝑟𝑎𝑚𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
𝑘𝑔 𝑜𝑓 𝑠𝑜𝑙𝑣𝑒𝑛𝑡
Molality Example Problem #1
Calculate the molality of a solution that
contains 15.7 g of NaCl in 100 g of water.
Molality Example Problem #2
Calculate the molality of a solution that
contains 20.0 g CaCl2 in 700 g of H2O.