Transcript Solution Concentration What is different between the glasses of Kool-aid? Solution concentration can be described generally Dilute - reduced in strength, weak, watered down. Concentrated –

Solution
Concentration
What is different between the glasses of
Kool-aid?
Solution concentration can be described
generally
Dilute - reduced in strength, weak,
watered down.
Concentrated – stronger, pure. Has less
water.
What is the problem with just using dilute
and concentrated as descriptions of the
solution concentration?
Is solution B dilute or concentrated?
Concentrated
Dilute
Solution A
Solution B
Solution C
The terms dilute and concentrated are
relative.
Scientists need a more precise way of
referring to the concentration of a
solution.
Solution concentration can be described
specifically
Do you remember the “mole” from
Stoichiometry?
What is a mole?
How might you use it to describe the
concentration of a solution?
Concentration can be represented by…
•Molarity
•Molality
•Percent by Mass
Molarity
The ratio of the moles of solute to
the volume of solution in liters.
Molarity (M) =
Moles of solute
Volume in Liters of solution
Used for most chemistry calculations of concentration
Molality
Molality = moles of solute per kg solvent
Molality (M) =
Moles of solute
kilogram of Solvent
Used for chemistry when volume of solvent is not constant
Percent by Mass
Percent by Mass = mass of solute divided
by mass of total solution
% by mass =
Mass (g) of solute
Mass of Solvent + Mass of Solute
Used for food, medicine, household cleaners and chemicals
How to Calculate Dilutions
Using molarity to calculate dilutions is
EASY.
Moles stays the same
Volume changes
Molarity changes
M1V1 = M2V2
Re-arrange to solve for the requested
information
How to read Molarity
6.0 M NaCl
Read: “6 molar solution of NaCl”
Can be abbreviated 6M solution
You must be careful to label the molarity
with a capital M so that it is not confused
with m for molality.
How to make a solution using molarity
(6M NaCl)
(a) Add 6 moles NaCl to
the volumetric flask.
How would you measure
that?
6moles NaCl 58.443 g NaCl
1 mole NaCl
= 351 g NaCl
How to make a solution using molarity
(6M NaCl)
(b) Add dH2O to
dissolve and mix the
NaCl
(c) Fill the flask with dH2O until you
reach the 1000mL line.
Types of Calculations with Molarity:
1. Finding concentration of a solution.
2. Finding the mass of solute needed.
3. Finding the volume of solution made.
Finding Concentration
 Antifreeze is a solution of ethylene glycol,
C2H6O2 in water. If 4.50 L of antifreeze contains
27.5 g of ethylene glycol, what is the
concentration of the solution?
27.5 g C2H6O2 1 mol C2H6O2
62.08 g C2H6O2 4.5 L
= 0.0984 mol/L or
0.0984 M C2H6O2
Finding Mass
What mass of sodium carbonate, Na2CO3,
is present in 50 ml of a 0.750M solution?
Conversion Factor
50 ml
1L
1000 mL
0.750 mol 105.99 g Na2CO3
1L
1 mol Na2CO3
= 3.97 g Na2CO3
Finding Volume
Conversion Factor
What volume of 1.50 mol/L HCl solution
contains 10.0 g of hydrogen chloride?
10.0 g HCl 1 mol HCl
36.46 g HCl
1L
1.50 mol
= 0.183 L or 183 mL
Practice
Problems
Practice Problems
1. A 0.750 L aqueous solution contains 90.0 g of
ethanol, C2H5OH. Calculate the molar
concentration of the solution in mol·L-1.
Practice Problem
2. What mass of NaCl are dissolved in 152 mL of a
solution if the concentration of the solution is
0.364 M?
Practice Problem
3. What mass of dextrose, C6H12O6 is
dissolved in 325 mL of 0.258 M solution?
Practice Problem
4. A mass of 98 g of sulfuric acid, H2SO4, is
dissolved in water to prepare a 0.500 M
solution. What is the volume of the
solution?
Practice Problem
5. A solution of sodium carbonate, Na2CO3,
contains 53.0 g of solute in 215 mL of
solution. What is its molarity?
Practice Problem
6. What is the molarity of a solution of HNO3
that contains 12.6 g of solute in 5.00 L of
solution?