Solutions: Concentration Chapter 14. Solution Homogenous mixture of 2 or more substances in single...
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Transcript of Solutions: Concentration Chapter 14. Solution Homogenous mixture of 2 or more substances in single...
Solutions:Solutions:ConcentrationConcentrationChapter 14Chapter 14
SolutionSolution
Homogenous mixture of 2 or more Homogenous mixture of 2 or more substances in single phasesubstances in single phase = 1 layer= 1 layer
Component present in largest amt = Component present in largest amt = solventsolvent
Other component(s) = Other component(s) = solutesolute Alloys, air are all solutions (solns)Alloys, air are all solutions (solns)
Colligative propertiesColligative properties
= change of mp, bp, osmotic pressure of = change of mp, bp, osmotic pressure of soln, change in vapor pressuresoln, change in vapor pressure
Irrespective of solute identityIrrespective of solute identity Dependent on concentrationDependent on concentration
ConcentrationConcentration
Molarity (M) = moles solute/L of solution Molarity (M) = moles solute/L of solution = mol/L= mol/L We’re all familiar with thisWe’re all familiar with this
Drawback Drawback won’t give you proper won’t give you proper amount of solvent used to make solnamount of solvent used to make soln
Molality (Molality (mm) better) better
ProblemProblem
Give the concentration (in M) of 0.0012 Give the concentration (in M) of 0.0012 grams of NaCl in 545 mL of watergrams of NaCl in 545 mL of water
MW of NaCl = 58.442 g/molMW of NaCl = 58.442 g/mol
MolalityMolality
Molality (Molality (mm) = moles ) = moles solute/kg of solventsolute/kg of solvent
Let’s look to the rightLet’s look to the right molality molality molarity molarity
Problem Problem
Give the concentration (in Give the concentration (in mm) of 0.0012 ) of 0.0012 grams of NaCl in 545 mL of watergrams of NaCl in 545 mL of water
Density of water @ 25Density of water @ 25°C = 0.9970 g/mL°C = 0.9970 g/mL MW of NaCl = 58.442 g/molMW of NaCl = 58.442 g/mol
Mole fractionMole fraction
Mole fraction of A Mole fraction of A (X(XAA) = n) = nAA/n/ntottot
Amt of component Amt of component A/total componentsA/total components
Soln contains 1.00 Soln contains 1.00 mol ethanol and 9.00 mol ethanol and 9.00 mol watermol water
ethanol
water
ethanol water
1.00X = = 0.100
(1.00+9.00)
9.00X = = 0.900
(1.00+9.00)
X + X = 1.000
Weight percentWeight percent
Ex: 46.1 g ethanol & Ex: 46.1 g ethanol & 162 g water162 g water
Commonly used in Commonly used in household products household products like vinegar & bleachlike vinegar & bleach
46.1gWeight % ethanol = 100% = 22.2%
(46.1g+162g)
solute mass100%
solution mass
ProblemProblem
• Concentrated sulfuric acid has a density of 1.84 g/cm3 and is 95.0% (w/w) H2SO4. MW H2SO4 = 98.079 g/mol. Calculate the molarity and the molality of this
solution.
Solution: molaritySolution: molarity
M78.11L
mL1000
mL1
cm1
cm
soln g84.1
acid 98.079g
mol
soln g0.100
acid 95.0g 3
3
Solution: molalitySolution: molality
m190 water1kg
g1000
acid g079.98
mol
waterg 5.0
acid g0.95
Problem Problem
• A 10.7 molal solution of NaOH has a density of 1.33 g/cm3 at 20°C. MW NaOH = 39.996 g/mol & MW H2O = 18.0153 g/mol. Calculate the mole fraction of NaOH, the
weight percentage of NaOH and the molarity of the solution.
SolutionSolution
M97.9L
mL1000
mL
cm
cm
soln g33.1
soln 1428g
NaOH 10.7mol
(w/w) NaOH %0.30%100 water1000gNaOH 428g
NaOH 428g
NaOH g428mol
39.996g NaOH mol7.10
162.0)55.5mol10.7mol
mol7.10(X
watermol5.5518.0153g
mol
1kg
1000g waterkg1
3
3
NaOH
More practiceMore practice
An aqueous soln of NaCl is created using An aqueous soln of NaCl is created using 133 g of NaCl diluted to a total soln 133 g of NaCl diluted to a total soln volume of 1.00 L.volume of 1.00 L. Calculate the molarity, molality, and Calculate the molarity, molality, and
mass percent of the soln, given a mass percent of the soln, given a density of 1.08 g/mL and MW of NaCl density of 1.08 g/mL and MW of NaCl = 58.442 g/mol.= 58.442 g/mol.
Solution Solution
massby %3.12%100solvent 947gNaCl g133
NaCl g133
40.2solvent kg947.0
1
58.442g
molNaCl g 133
solvent kg 0.947 solvent 947g
solvent 947gNaCl 133g-soln g101.08
L
soln g101.08
1L
1000mL
mL
soln 1.08g
M28.2L00.1
1
58.442g
mol33g1
3
3
m
Part per millionPart per million
= PPM (in grams)= PPM (in grams) Ex: 1.0 ppm = 1.0 g of substance in Ex: 1.0 ppm = 1.0 g of substance in
system w/ 1.0 million g total masssystem w/ 1.0 million g total mass @ STP water density @ STP water density 1.0 g/mL 1.0 g/mL So, mg/L and ppm are So, mg/L and ppm are Used predominately by environmental Used predominately by environmental
and analytical chemistsand analytical chemists
Solution processSolution process
One can add only so much solute to One can add only so much solute to solventsolvent
Since no more dissolves Since no more dissolves soln said to soln said to be be saturatedsaturated NaCl = 35.9 g/100 mL water (25NaCl = 35.9 g/100 mL water (25°C)°C)
Albeit, nothing changes visually, soln is Albeit, nothing changes visually, soln is constantly dissolving and re-solidifying constantly dissolving and re-solidifying ionsions
Solution processSolution process
Essentially, Essentially, solubilitysolubility = solute concentration in = solute concentration in equilibrium w/undissolved solute in saturated equilibrium w/undissolved solute in saturated solnsoln
Unsaturated soln Unsaturated soln = soln w/less than saturated = soln w/less than saturated amt of soluteamt of solute NaCl < 35.9 g/100 mL water (25NaCl < 35.9 g/100 mL water (25°C)°C)
Supersaturated solnSupersaturated soln = soln w/more solute = soln w/more solute than sat. solnthan sat. soln NaCl > 35.9 g/100 mL water (25NaCl > 35.9 g/100 mL water (25°C)°C)
Making supersaturated Making supersaturated solutionssolutions
Pour in excessive amount of solutePour in excessive amount of solute Heat up the solnHeat up the soln Stir until all solute dissolvesStir until all solute dissolves
Cool it slowly Cool it slowly No shaking, no jarring of solnNo shaking, no jarring of soln
Gives lower freezing pointGives lower freezing point
Once disturbed (energy in), causes crystallization to occur Once disturbed (energy in), causes crystallization to occur excess crystallized out of solnexcess crystallized out of soln
ExothermicExothermic Heat packs of sodium acetate (can reach 50Heat packs of sodium acetate (can reach 50°C!)°C!) http://www.npr.org/programs/wesun/features/2001/dec/heatpack/0http://www.npr.org/programs/wesun/features/2001/dec/heatpack/0
11229.heatpack.html11229.heatpack.html Your second lab deals with thisYour second lab deals with this
Liquids as solutesLiquids as solutes
Miscible = mixableMiscible = mixable Immiscible = unmixableImmiscible = unmixable Used in language too:Used in language too:
Mestizo, mischlingMestizo, mischling Ability to dissolve based Ability to dissolve based
on similar polarities (or on similar polarities (or lack thereof) of lack thereof) of solute/solventsolute/solvent
Like dissolves in likeLike dissolves in like
Let’s try theseLet’s try these
Considering intermolecular forces, give reasons for the following observations:
a) Octane, C8H18, is very miscible with CCl4. b) Methanol, CH3OH, mixes in all proportions
with water. c) Sodium bromide is not very soluble in diethyl
ether (CH3CH2—O—CH2CH3). d) Octanol, C8H17OH, is not very soluble in
water.