Measuring solubility
Saturated and Unsaturated
• The solubility of a substance refers to the
maximum amount of that substance that can be
dissolved in a given quantity of solvent at a certain
temperature.
• A solution that contains precisely the maximum
mass of solute that can be dissolved in a
particular volume of solvent at a particular
temperature is called a saturated solution
• Unsaturated solution – a solution that contains
less that the maximum mass of solute.
• Supersaturated solution – a solution that
contains more than the maximum amount of
solute.
• Solubility is measured in grams per 100
grams of water (g/100g)
• Most salts are soluble in water to some
extent
• Solubility is influenced by the temperature
of the solution
• If a substance does not dissolve in water
it is insoluble
Solubility curve
• Used to represent
the solubility of a
particular
substance at a
given temperature.
• The graph can be
used to measure
the amount of
solute present in a
solution of a
particular
temperature
• Any point on the curve indicates a
saturated solution.
• Any point below the curve indicates
an unsaturated solution.
• Any point above the curve indicates a
supersaturated solution.
Questions - Solubility Curves
• What is the solubility
of KNO3 at 80C?
• Which substance has
the highest solubility
at 100C?
• At what temperature
is NaNO3 solubility
100g/100g of water?
• At 40C, what would
be the solubility of a
Super, saturated and
unsaturated solution
of NaCl?
Crystallisation
• When something cools the solute may no
longer stay dissolved in the solvent and will
come out as crystals
• This is called crystallisation
• Kidney stones are formed when minerals in
urine come out of the solution and form
crystals.
Calculations
• An 80g sample of
NaNO3 is added to
200g of H2O at 20 C.
Use the solubility
curve to calculate
how much more
NaNO3 needs to be
added to the solution
saturated with NaNO3
at 20C
• Pg 207 solubility
curve
Solution
• 85g of NaNO3 at 20C to 100g to make
saturated
• 85 X 2 = 170g of NaNO3 in 200g of water
• 170 (needed – 80(already added) = 90g
need to be added
Calculations
• What happens in a solution containing 50g of
KNO3 in 100g of water that is allowed to cool
from 40C to 20C? Use pg 207 S curve
• At 40C normally solubility would be 70g/100g
of water BUT we have 50g/100g of water
• At 20C solubililty is 35g/100g of water
• 50 – 35 = 15g will crystallise out of solution
Homework
• Pg 211
• Q 1,2,3,4,5,6,7
Solubility rules
• All compounds of the ammonium ion
(NH4+), and of Alkali metal (Group IA)
cations, are soluble.
• All nitrates and acetates (ethanoates) are
soluble.
• All chlorides, bromides and iodides are
soluble EXCEPT those of silver, lead and
mercury(I).
• All sulphates are soluble EXCEPT those of
silver, lead, mercury(I), barium, strontium
and calcium.
Solubility rules
• All carbonates, sulfites and phosphates are
insoluble EXCEPT those of ammonium and Alkali
metal (Group IA) cations.
• All hydroxides are insoluble EXCEPT those of
ammonium, barium and alkali metal (Group I)
cations.
• All sulfides are insoluble EXCEPT those of
ammonium, Alkali metal (Group I) cations and
Alkali earth metal (Group II) cations.
• All oxides are insoluble EXCEPT those of calcium,
barium and Alkali metal (Group I) cations; these
soluble ones actually react with the water to form
hydroxides (hydrolyse).
Solubility of Gases
• Gases are much less soluble in water than
solid substances.
• It depends of the temperature of the liquid
and the pressure of the gas.
• The higher the temperature the lower the
solubility of the gas.
• Solubility increases with increasing
pressure
Concentration
• Concentration is the amount of solute
dissolved in a given solvent.
• High concentration – high ratio of
solute:solvent. This is called a concentrated
solution
• Low concentration – low ratio of solute:solvent
• A dilute solution is one which has a low
concentration
Concentration
• Concentration is also defined as the
amount of solute per volume of solvent
• A concentrated solution of hydrochloric
acid contains 37g in a 100g solution.
• A dilute solution of hydrochloric acid
contains 10g of HCl in 100g solution.
Unit Conversion
/1000
microlitre
uL
x1000
/1000
millilitre
mL x1000
/1000
Litre
L x1000
kiloLitre
kL
Measuring Concentration
Concentration can be measured in several ways
1. Concentration = mass of solute in grams (g)
volume of solution in litres (L)
Concentration = g/L or gL-1
Measuring Concentration
2. Another measure of concentration is
molarity or molar concentration
Molarity is defined as the number moles of
solute particles per litre of solution
The symbol for molarity is M 1M is One
Molar.
One Litre of a 1M solution of ethanol
contains 1 mole of ethanol
Molar Concentration (molL-1) or
Molarity(M)
• The number of moles per Litre of a
solution is known as the molar
concentration.
• There is a relationship between mol and
volume and molarity. Using units can you
guess?
Concentration (molL-1) = mol/ volume in (L)
C= n
V
n = cV
Calculations
• Calculate the molar concentration of a
solution that contains 0.105mol of KNO3
dissolved in 200mL of solution
1. Convert 200mL to L = 200/1000 = 0.2L
2. 0.105mol = 0.525 mol/L or M
0.2L
Calculations
• Calculate the amount, in moles, of
ammonia(NH3) in 25.0mL of 0.3277M
(mol/L)
1. Convert 25 /1000 = 0.025L
2. 0.3277 mol/L x 0.025L = 0.00819 mol
Dilution
• The process of adding more solvent to a
solution is called dilution
• You are not changing the amount of solute but
the amount of solvent
• Therefore the amount (grams) of solute stays
the same
• When a substance is diluted the solute particles
have more space between them
The same amount
of solute in each
flask but they have
different
concentrations and
volumes
Formula
• When we dilute something we can
calculate either the new concentration or
volume. This results in a formula called the
dilution formula.
C1V1 = C2V2
Calculations
• The concentration of a seaweed extract in a
bottle of fertiliser is 9.0g/L. When used to
fertilise plans, the seaweed fertiliser must be
diluted, if 10mL of seaweed is diluted to fill 2L
what is the new concentration
• 10mL /1000= 0.01L
• C1 = 9.0g/L V1 = 0.010L
• C2?
V2 = 2L
• 9.0g/L x 0.01L = c2 x 2L
• 9.0g/L x 0.01L = c2 = 0.045g/L
2L
Calculations
• How much water must be added to 30mL of 2.5
mol/L solution of NaOH to dilute it to 1 mol/L
• The number of moles of solute does not change
dilution
C1 = 2.5 mol/L v1 = 30mL
c2 = 1 mol/L v2 = ?
C1v1 = c2v2
V2 = c1v1
c2
2.5mol/L x 0.030L = 0.075L
1 mol/L
75mL – 30mL = 45mL is added
Homework
• Pg 215 Q 9 - 13