Solubility and Why Things Dissolve. Solutions A homogeneous mixture solute - dissolves (usually...
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Transcript of Solubility and Why Things Dissolve. Solutions A homogeneous mixture solute - dissolves (usually...
Solubility and Why Things Dissolve
Solutions
•A homogeneous mixturesolute - dissolves (usually smaller amount)
solvent – causes solute to dissolve(usually larger amount)
Types of solutes
•Electrolytes▫ Ionic compounds are hydrated▫Electrolytes conduct electricity in aqueous solutions
•Nonelectrolytes▫Molecular solutions▫Non-conductive
Types of Solutions•Solid solution (solid solvent)•Gaseous solution (gas solvent)•Liquid solution (liquid solvent)
Aqueous Solution (water solvent)
Solubility – does it dissolve?•Soluble
▫Strong electrolyte▫Strong Acids and Bases
• Insoluble (misleading)▫Always some solubility
Is lead soluble in water Why don’t we use lead pipes
▫Weak electrolyte▫Weak acids and bases
How much dissolves?SaturationUnsaturated
Less than the maximum amount of solute dissolved
Saturated Maximum amount of solute
dissolved(extra precipitates out)
SupersaturatedMore than the maximum
amount of solute dissolved
Solubility Curve
•Measure how much solute will dissolve in 100. g of water (solvent) at a particular temperature
g solute vs temperature100. H2O
Solubility Curve - Solids
The solubility of solids increases with temperature
Saturatedonline Unsaturated
underline
SupersaturatedOverline
Solubility Curve- Gases
The solubility of gases decreases with temperature
Water’s Unique Properties
•Universal solvent•Solid less dense than liquid•High boiling point•High surface tension
Why does water have these properties?
•Water is a polar Water is a polar moleculemolecule
•Water can form a Water can form a Hydrogen BondHydrogen Bond
Polar Molecule
•A molecule A molecule with a + with a +
and a – endand a – end
H is +H is + O is –O is –
Hydrogen bond
•+ H atoms of + H atoms of one molecule one molecule are attracted are attracted toto
•- O atoms of - O atoms of another another moleculemolecule
Why does it dissolve? “Like dissolves like”
•Polar dissolves polar▫Different ends
•Non-polar dissolves non-polar▫Same endsWill this dissolve? CO2 in H2O KBr in H2O
CO2 in CH4 KBr in CH4
Solvation
•Dissociation – decomposition of a ionic compound into hydrated ions
•Hydrated – charged ions surrounded by water molecules
•Solvation – processing of dissolving
Dissolving Salt Crystal
Lab: Solubility
Solution concentrationThe amount of solute dissolved in a specific
amount of solution
1. Written as a % (for large amounts)
g solute x 100%g solution
2. Molarity (M) Moles solute L solution
3.Molality (m) moles soluteKg solvent
Colligative Properties
•Properties that depend on the amount of solute added to solution
•Boiling point elevation•Freezing point depression
Freezing point depression
T = Kf x m x iChange in temperatureKf = freezing point constant
Molalityi= number of particles in solution
Problems
•Calculate the percent of a solution that is made of 14.6 g NaCl in 123 g water.
• If a solution is 67.3 % KI, how many g of KI are added to 376 g solution?
Problems
•Calculate the molarity of a solution with 30.0 g NaCl with water added to make 250 mL solution
•Calculate the molarity of a solution with 45.7 g KCl to make 500 mL solution
More
•Calculate the g to make 600. mL of a .35 M NaCl.
•Calculate the g to make 550 mL of a .36 M KOH
Making solutionsShow calculations to make 100 mL of .10 M using NaOH
Then go back and make it and label the flask for future use
Dilution
If you have a solution and want it at a lower Molarity
M1 x V1 = M2 x V2
Problems
•How would you dilute a 2.5 M stock solution of H2SO4 to make 200 mL of .15 M H2SO4?
Making your dilution
•Show calculation for maing 100 mL of .1 M HCl from a 2.5 M stock solution
•Then go back and make it and label the flask for future use.
Molarity•Moles per liter•M = mol / liter•Liters x Molarity = moles
L x mol = mol L
•Moles / Molarity = litersMol x 1 = L mol / L
Calculate molarity, molality
MolarityMoles per liter
Moles SoluteLiters of solution
Molality
Mole per kilogram
Moles soluteKilograms solvent
Sol
ubil
ity
(g s
olut
e/10
0g H
2O)
Sol
ubil
ity
(g s
olut
e/10
0g H
2O)
Notice at 90 C there is more solute than solvent!
This solid has a lower solubilityIn hot water than cold
There is almost no differenceIn cold and hot solubility
Temperature ºC
GasesS
olub
ilit
y (g
sol
ute/
100g
H2O
)
Warmer temperature meansLess DO (dissolved oxygen)
Poor fishies
So
lub
ility
(g
solu
te/1
00g
H2O
)
How much KNO3 will dissolve in 100.0 g of water at 80.0 C?
How much KNO3 will precipitate when a saturated solution at 80.0 C is cooled to 20.0C?
How much sugar will dissolve in 50.0 g of water at 60.0 C?
Sol
ubil
ity
(g s
olut
e/10
0g H
2O)
How much sugar will precipitate if 760 g of a saturated solution at 60 C is cooled to 20 C.
140. g
160. g