Grade 8 Integrated Science Chapter 10 Lesson 2 on properties of solution, solubility, concentration, solvents, and solutes. Understanding how to change solubility of a solute in a solvent.

1. Properties of Solution
Ch 10.2 (p342 – 350)

2. Parts of Solution
• Dissolving is the process of mixing one
substance into another to form a solution.
• There are two terms to refer to the
substances that make up a solution
• Solvent is the substance that exists in the
greatest quantity in a solution
• All other substances in a solution are
solutes

3. • Air
– What is the solvent?
– What is the solute?

4. Types of Solutions
• Solutions can exist is all three states of
matter – solid, liquid, and gas
• The state of the solvent determines the
state of the solution because it exists in
the greatest quantity

6. Water as a Solvent
• Water is one of the few substances on
Earth that exists naturally in all three
states – solid, liquid, gas
• Much of the water found on Earth is not
pure
• Water almost always exists as a solution
• Why is this?

7. The Polarity of Water
• A water molecule is a covalent compound held
together by the sharing a electrons between the
atoms
• However the electrons are not equally shared
• Electrons in the hydrogen-oxygen bond are
pulled more closely to the oxygen
• This unequal sharing gives the oxygen end of
the water molecule a slight negative charge
• It also gives the hydrogen end a slight positive
charge
• Thus, the water molecule is polar

8. The Polarity of Water
• A polar molecule is a molecule with a
slightly negative end and a slightly positive
end

9. Like Dissolves Like
• Water is often called the universal solvent
because it dissolves many different substances
• However, water cannot dissolve everything
• Polar solvents dissolve polar solutes easily
• Nonpolar solvent dissolve nonpolar solutes
easily
– This is summarized by the phrase “like dissolves like”
• Because water is a polar solvent, it dissolves
most polar and ionic solutes

10. Polar Solvents and Polar Molecules
• Rubbing alcohol, or isopropyl alcohol, is a substance
that is used as a disinfectant
• Molecules of rubbing alcohol are also polar
• Therefore, when rubbing alcohol and water mix, the
positive ends of the water molecules are attracted to the
negative ends of the alcohol molecules.
• Similarly the negative ends of the
water molecules are attracted to the
positive ends of the alcohol molecules
• In this way, alcohol molecules
dissolve in the solvent

11. Polar Solvents and Ionic
Compounds
• Many ionic compounds are also soluble in water.
• Recall that ionic compounds are composed of
alternating positive and negative ions
– Sodium Chloride (NaCl) is an ionic compound
composed of sodium ions (Na+) and chloride ions
(Cl-)
• When sodium chloride dissolves these ions are
pulled apart by the water molecules
– The negative ends of the water molecules attract the
positive sodium ion
– The positive ends of the water molecule attract the
negative chloride ions.

13. Concentration – How much is
dissolved
• Have you ever tasted soup and wished it
has more salt in it?
– In a way your taste buds were measuring the
amount, or concentration, of salt in the soup.
• Concentration is the amount of a particular
solute in a given amount of solution
– In soup, salt is a solute
– Soup with less salt has a lower concentration
of salt

14. Concentration and Dilute Solutions
• One way to describe the saltier soup id to say
that it is more concentrated
• The less saltier soup is more dilute
• Concentrated and dilute are one way to describe
how much solute is dissolved in a solution
– However, these terms don’t tell us the exact amount
of solute dissolved

15. Describing Concentration Using
Quantity
• A more precise way to describe concentration is
to state the quantity of solute in a given quantity
of solution.
• When a solution is made of a solid dissolved in a
liquid, such as salt in water, concentration is the
mass of solute in a given volume of solution.
• Mass is usually stated in grams and volume is
usually stated in liters.
– For example, concentration cam be stated as grams
of solute per 1 L of solution
– However, concentration can be stated using any unit
of mass or volume

16. Calculating Concentration – Mass
per Volume
• One way that concentration can be
calculated is by the following equation
– Concentration (C) = mass of solute (m)
volume of solution (v)
– To calculate, you must know the mass of
solute and the volume of solution that
contains the mass.

17. Concentration – Percent by Volume
• Not all solutions are made of a solid dissolved in a liquid.
• If a solution contains only liquids or gases, its
concentration is stated as the volume of solute in a given
volume of solution
• In this case, the units of volume must be the same –
usually mL or L.
• Because the units match, the concentration can be
stated as a percentage.
• Percent by volume is calculated by dividing the volume
of the solute by the total volume of the solution and then
multiplying the quotient by 100.

18. • What is the percent by volume?
– If there are 1000mL of solution, how much
isopropyl alcohol and water are in the
solution?

19. Solubility – How much can
dissolve?
• Have you ever put too much sugar into a glass
of iced tea?
– Not all the sugar dissolves
– This is because these is a limit to how much solute
(sugar) can be dissolved in a solvent (water)
• Solubility is the maximum amount of solute that
can dissolve in a given amount of solvent at a
given temperature and pressure
– If a substance has a high solubility, more of it can
dissolve in a given solvent

20. Saturated and Unsaturated
Solutions
• If you add water to a dry sponge, the sponge
absorbs the water.
– If you keep adding water, the sponge becomes
saturated. It can’t hold anymore water
• This is analogous, or similar, to what happens
when you stir too much sugar into ice tea
• Some sugar dissolves, but the excess sugar
does not dissolve
– The solution is saturated

21. • A saturated solution is a solution that
contains the maximum amount of solute
the solution can hold at a given
temperature and pressure
• An unsaturated solution is a solution that
can still dissolve more solute at a given
temperature and pressure

22. Factors that Affect How Much Can
Dissolve
• Can you change the amount of a
particular solute that can dissolve in a
solvent? Yes
• Recall the definition of solubility –
– The maximum amount of solute that can
dissolve in a given amount of solvent at a
given temperature and pressure
• Changing either temperature or pressure
changes how much solute can dissolve in
a solvent

23. Effect of Temperature
• The solubility of most solid substances
increases with temperature
– However, some can become less soluble as
temperatures increase
• How does temperature affect the solubility of a
gas in a liquid?
– Recall soda, or soft drinks, contain carbon dioxide, a
gas solute dissolved in liquid water
– The warmer the soda the more carbon dioxide
bubbles out than when it is cold
– This is because the solubility of a gas in a liquid
decreases when the temperature of the solution
increases

25. Effect of Pressure
• What keeps carbon dioxide in an unopened can
of soda?
• In a can, the carbon dioxide in the space above
the liquid soda is under pressure
• This causes the gas to move to an area of lower
pressure – the solvent
• The gass moves into the solvent, and a solution
is formed
– When the can is opened, this pressure is released
and the carbon dioxide gas leaves the solution.
– *Pressure does not affect the solubility of a solid
solute in a liquid

26. How Fast a Solute Dissolves
• Temperature and pressure can affect how much
solute dissolves
• If solute and solvent particles come into contact
more often, the solute dissolves faster
• There are three ways to increase how often
solute particles contact solvent particles
– Stirring
– Crushing
• *Stirring and crushing will not make more solute dissolve;
They’ll only increase how fast it dissolves
– Increasing temperature