JMJ
7-2 Solutes and Solubility, Theme: Changes and Reactions
Classification of Matter – classified by units that make it
Elements: made up of atoms which all have same identity, may or may not be chemically
combined
Compounds: made from atoms of 2 or more elements that are combined chemically
(atoms are bonded together)
Molecules: made of 2 or more atoms that are combined chemically, the atoms can be the
same or different elements
Substance: an element or compound, can’t be reduced to more basic components by
physical processes
Mixtures
Material made up of 2 or more substances that can be separated by physical means.
Each substance in a mixture keeps its own properties and identity
Heterogeneous mixture
Different materials can be easily distinguished
Not uniformly mixed
Examples: Granite, pizza, Inside of your locker or backpack
Solutions
Homogeneous mixture
Two or more substances are uniformly mixed together
Solution particles never settle to bottom of container
Remain constantly and uniformly mixed
Solution terms
Solute: substance being dissolved, less than 50% of a solution
Solvent: substance dissolving the solute, present in largest amount
Alloy – a solution of a metal and another element (usually another metal)
Solids dissolving in liquids
Dissolving of a solid in a liquid occurs at the surface of the solid
Solids dissolve from the outside to the center
The more surface there is, the faster something dissolves
A large block has less surface available (less surface area) than the same block broken
into pieces
Rate of Dissolving
Rate of solubility depends on how the solute is dissolved
Stirring speeds up dissolving –brings more fresh solvent into contact with more
solute, also moves solute particles around in the solvent
Grinding a solute speeds dissolving of solid in liquid - large crystals become small
ones and solvent has more surface area to work on
Increasing the temperature of solvent increases rate at which most solids dissolve increasing temp speeds up action of molecules of the solvent and the solute
Solubility
Physical property of matter that relates to the ability of a solute to dissolve in a solvent
A measure of how easily or how quickly a solute dissolves in a solvent
Something that is insoluble does not dissolve
Rate of solubility
mass of solute dissolved/time to dissolve (g/min)
To calculate the rate of solubility divide the mass of the solute by the time it takes to
dissolve
Rate of solubility units: g/min or g/sec
Rate of solubility is affected by temperature
Miscibility
A measure of how easily or how quickly a liquid solute dissolves in a liquid solvent
Water and oil are immiscible (they don’t dissolve in each other)
Concentration
A measure of the amount of one substance in a specific volume of another substance.
Concentration units: g/mL
Ex. Grams of solute per mL of solvent
Types of solutions based on amt. of solute dissolved
Saturated solution - solution that has dissolved all the solute it normally can hold at a
given temperature
If you heat the mixture to a higher temp, more solute can dissolve - as temp.
increases, amt. of solute that can dissolve increases
Unsaturated solution - any solution that can dissolve more solute at a given temp.
Each time a saturated solution is heated to a higher temp, it may become
unsaturated
Supersaturated solution - contains more solute than a saturated one has at that
temperature
This kind of solution is unstable
Saturation point
Point where no more solute will dissolve in a solution
Add a solute crystal to solution:
If crystal dissolves, solution is unsaturated
If crystal doesn’t dissolve, solution. is saturated
If excess solute comes out, solution is supersaturated
Read and interpret data tables –
Which solutions are saturated or unsaturated?
What does a solution look like if all the solute dissolves?
What is maximum mass dissolved?
Between which masses is the saturation point?
Calculate the rate of solubility
Measurement
Mass with a triple beam balance (g)
Volume with a graduated cylinder or calculated using a formula (mL or cm3)
Length with a ruler (cm or m)
Temperature with a thermometer (°C)
2
Summary:
In Investigation 1, it was discovered that different compounds possess different
solubilities. The unique combinations of elements that make up each compound results in the
different solubility of each compound. The different combination of elements determines that
each compound is soluble in a solvent, like water, up to a different concentration. In
Investigation 2, it was discovered that stirring increases the solubility of a solute. More of a
solute can be dissolved in a solvent when the solution is stirred as compared to when it is not
stirred. In Investigation 3, it was discovered that changing the temperature of the solvent affects
the solubility of a solute. More solute can dissolve in a higher temperature solvent than in a
lower temperature solvent.
In Investigation 1, students attempted to dissolve differing masses of the different solutes.
Each solute reached a different saturation point beyond which no more solute dissolved. Solutes
are able to dissolve and form solutions only up to a concentration that corresponds to their
specific saturation point. Any amount of solute greater than the saturation point will not dissolve.
In Investigation 2 and 3, the effects of stirring and temperature on the rate of solubility
were explored. Stirring increases the rate of solubility of a solute. A solute sill take less time to
dissolve in a solvent if stirred as compared to a solution that is not stirred. The rate of solubility
usually increases as the temperature of the solvent increases and usually decreases as the
temperature of the solvent decreases.
3