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.