Chapter 8 Solutions When substances dissolve to form solutions the properties of the mixture change 81 A solution is a type of mixture 82 The amount of solute that dissolves can vary 83 Solutions can be acidic basic or neutral ID: 269253
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Unit: Chemical InteractionsChapter 8: SolutionsWhen substances dissolve to form solutions, the properties of the mixture change.
8.1: A solution is a type of mixture
8.2: The amount of solute that dissolves can vary
8.3: Solutions can be acidic, basic, or neutral
8.4: Metal alloys are solid mixturesSlide2
8.2: The amount of solute that dissolves can varyBefore, you learnedSolutions are a type of mixtureA solution is made when a solute is dissolved in a solventSolutes change the properties of solventsNow, you will learn
About the concentration of a solution
How a solute’s solubility can be changed
How solubility depends on molecular structure
8.2: The amount of solute that dissolves can varySlide3
Review / warm-upTrue or False?Dissolving a solute in a solvent is a chemical changeFalse: physical changeAdding a solute to a solvent raises the solvent’s boiling point
True
The
particles in a solution are larger than the particles in a suspensionFalse
: smaller
8.2: The amount of solute that dissolves can varySlide4
A solution with a high concentration contains a large amount of soluteOcean water vs well waterBoth contain salt (solute)Ocean water contains more
salt (solute) than the well water
The more solute, the higher concentration of the solute
Concentration: depends on the amount of solute dissolved in a solvent at a particular temperature
Adding lemonade mix to water
More powder you add, the higher concentration of the drink
8.2: The amount of solute that dissolves can varySlide5
Degrees of Concentration“Dilute solution
”:
a solution that has a
low concentration of soluteWell water is a “dilute solution” - there is salt dissolved in the water but at a low concentration
Add more solvent, or pure water, you can dilute the solution more
A “
concentrated solution
” has a
large
amount of solute
A “saturated solution
” – when no more solute can be dissolved into the solvent – it can’t “hold” any more at that temperature
If it contains less than this maximum amount, it is a “unsaturated solution”
8.2: The amount of solute that dissolves can varySlide6
Supersaturated Solutions“Supersaturated Solution”: a solution that contains more dissolved solute than is normally possibleCan occur if more solute is added while the temperatures is raised, then the solution is slowly cooled, the solute can remain dissolvedThis solution is unstable
If the solution is disturbed, or more solute is added in the form of a crystal, the excess solute will quickly solidify and form a precipitate
Ex: chemical heat pack –
sodium acetate and water
(1
st
)(
2
nd
–how)Bag contains a solution of sodium acetate (solute) and water (solvent)
When heated, the excess sodium acetate can dissolve into the water completely
supersaturated solution
Heat pack is activated by bending it – disturbing the solution, solidifying the sodium acetate and releasing a large amount of heat over a long period of time (liquid
solid releases heat)
8.2: The amount of solute that dissolves can vary
Link
– saturated, unsaturated, supersaturated, crystallizationSlide7
SolubilityThe amount of a substance that will dissolve in a certain amount of solvent at a given temperatureEx: household ammonia (solution) is ammonia (solute) and water (solvent)A large amount of ammonia can dissolve in water
ammonia has a
high solubility in water
Ex: carbon dioxide can dissolve in water, but only a small amount
Low solubility
in water
Oils do not dissolve in water at all
Insoluble
in water
The amount of solute needed to make a saturated solution depends on the solubility of a solute in a particular solvent
If the solute is highly soluble, a lot of solute will be needed for a saturated solution, and the saturated solution will be very concentrated
If the solute has a low solubility, little solute is needed for a saturated solution, and the saturated solution will be dilute
8.2: The amount of solute that dissolves can varySlide8
The solubility of a solute can be changed…in two ways:Change the temperatureRaise the temperature of the solute – most solids are more soluble at higher temperatures
Change the pressure
The solubility of gases in a liquid solvent increases at high pressure
8.2: The amount of solute that dissolves can varySlide9
Temperature and SolubilityIncrease temperature effects on most solid substances:Solid solutes will dissolve more quickly
A greater amount of the solid dissolves in a given amount of solvent
Opposite true for gases! Increase temperature:
Gases become less soluble in water
Warming tap water – as it approaches boiling point air bubbles come out of solution and rise to the top!
Recall
: to supersaturate a solution, must raise the temperature first, then it cools slowly
The solid is less soluble in the cooler solution, but has not yet formed a precipitate
Consequences in real life:
a factory takes lake water for use as a coolant – returns warmer water to lake
Dissolved oxygen content
drops
bad for some marine life that use oxygen to breathe!
8.2: The amount of solute that dissolves can varySlide10
Temperature and Solubility8.2: The amount of solute that dissolves can vary
Solute
Inc. Temp
Dec. Temp
Solid
Inc. in solubility
Dec.
in solubility
Gas
Dec.
in solubility
Inc. in solubilitySlide11
Pressure and SolubilityPressure change usually only affects gasesSolubility of any gas increases at higher pressuresDecreases at lower pressuresEx: Soda – CO2 is added at higher pressure than typical air
When you open it – the CO2 bubbles fizz out
Ex: the bends – normal air we breathe: 78% N2, 21% O2
Under water pressure is higher, so N2 solubility into blood is higher
Rise to surface, the N2 comes out of solution, forming bubbles in diver’s blood vessels!
Avoidable?
8.2: The amount of solute that dissolves can varySlide12
Pressure and Solubility8.2: The amount of solute that dissolves can vary
Solute
Inc. Pressure
Dec. Pressure
Solid
No effect
o
n solubility
No effect
o
n solubility
Gas
Inc.
in solubility
Dec. in solubility
(Generic Graph:)Slide13
Solubility depends on molecular structureEx: oil and water do not mix – they have different molecular structuresWhen a substance dissolves, its molecules or ions separate from one another and become evenly mixed with molecules of the solventWater contains polar covalent bonds (negative and positive regions)
Oil is non-polar
Therefore their molecules are not attracted to each other
Sugar is polar, and highly soluble in water
Ionic compounds are soluble in water, also (ions are charged)
8.2: The amount of solute that dissolves can vary
Polar solvents dissolve polar solutes
Nonpolar
solvents dissolve
nonpolar
solutes
“Like dissolves like”