general chemistry-chapter 14

8/12/2019 General Chemistry-Chapter 14

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Chapter 14Chapter 14

SolutionsSolutions


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14.1 General properties of solutions14.1 General properties of solutionssolution a system in which one or more

substances are homogeneously mixed ordissolved in another substance

two components in a solution:solute the component that is dissolved or

is the least abundant componentsolvent the dissolving agent or

the most abundant component

the properties of a true solution:1. the mixture of two or more components is

homogeneous and have a variable composition

2. the dissolved solute is molecular or ionic in size3. it is either colored or colorless and is usually

transparent4. the solute is uniformly distributed throughout

the solution and will not settle out with time5. the solute can generally be separated from the

solvent by purely physical means


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ex. sugar solution 10 g or 20 g of sugar in 100 mL of water every portion of the solution has the same

sweet taste if no solvent is lost, the solution will taste

and appear he same a week or month later carefully evaporating water, the sugar can

be recovered ex. potassium permanganate KMnO 4 solution

the purple color disperses until it is evenlydistributed throughout the solutionsolution permanency is explained in term ofkinetic-molecular theory: both solute andsolvent particles are in constant randommotion that is energetic enough to preventthe solute particles from settling out underthe influence of gravity


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14.2 Solubility14.2 Solubilitysolubility the amount of solute that will dissolve

in a specified amount of solvent understated condition all radiations travel atthe same speed

ex. 36 g of NaCl will dissolve in 100 g of waterat 20 oC solubility of NaCl in water is

36 g/100 g H 2O at 20 oCqualitative description of solubility:

very soluble, moderately soluble,slightly soluble, insoluble

miscible liquids that are capable of mixingand forming a solution

immiscible those that do not form solution orare generally insoluble in each other

ex. oil and water are immisciblewater and ethanol are miscible

the quantitative expression for theamount of dissolved solute in a

particular quantity of solvent isknown as the concentration of asolution


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general guidelines for the solubility of commonionic compounds (salts)


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14.3 Factors related to solubility14.3 Factors related to solubilitymany variables are involved in the solubility of asubstance, some factors related to solubility areexamined 1. the nature of the solute and solvent

like dissolve like is a general rule polar or ionic substances tend to be more

compatible with other polar substances

nonpolar substances tend to be compatible withother nonpolar substances and less misciblewith polar substancesex. NaCl is more soluble in water than in ether,

hexane or benzene pentane is slightly soluble in water but is

soluble in ether or benzenesolution formation between

polar substance

NaCl dissolves in water NaCl(crystal)

Na +(aq) + Cl -(aq)


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2. the effect of temperature on solubility

for most solids dissolved in a liquid, an increasein temperature results in increased solubilitythere are some exceptionsthe solubility of a gas in water usuallydecreases with increasing temperature


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3. the effect of pressure on solubilitychanges in pressure have little effect on thesolubility of solid in liquids or liquids in liquids, but have marked effect on the solubility ofgases in liquidsthe solubility of a gas in a liquids directly

proportional to the pressure of that gas abovethe solution

ex. carbonated beverages CO 2 in water at a specific temperature there is a limit to theamount of solute that will dissolve in a givenamount of solventreaching this limit the resulting solution is said to

be saturated solutionex. adding 40 g KCl to 100 g H 2O at 20 oC34 g KCl dissolves and 6 g KCl undissolved

solute (undissolved) solute (dissolved)saturated solution contains dissolved andundissolved solute

unsaturated solution contains less solute per unitof volume than does its corresponding saturatedsolution

ex. adding 40 g KCl to 100 g H 2O at 20 oC34 g KCl dissolves and 6 g KCl undissolved if the solution heated to 50 oC, all the salt

will dissolve and the solution is unsaturated


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in some circumstances, solutions can be preparedthat contain more than needed for a saturatedsolution at a particular temperaturethese solution are said to be supersaturated

supersaturated solutions are unstabledisturbances will cause the supersaturatedsolution to return saturation releasing heatex. 14.1 will a solution made by adding 2.5 g

CuSO 4 to 10 g H 2O be saturated orunsaturated at 20 oC?

solubility of CuSO 4 at 20o

C: 21 g/100 g H 2Othat is, 2.1 g/10 g H 2Oso, this is a saturated solution


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14.4 Rates of dissolving solids14.4 Rates of dissolving solidsthe rate at which a solid dissolve is governed by1. the size of the solute particles

a solid can dissolve only at the surfacethe surface-to volume ratio increases as sizedecreases, small crystals dissolve faster thanlarge one

2. the temperaturethe rate of dissolving of a solid increases withtemperature

the solvent molecules move more rapidly athigher temperatures and strike the solid surfacesmore often and harder, causing the rate ofdissolving increases

3. the concentration of the solutionas the concentration of the solution increases and

the solution becomes more nearly saturated with


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the solute, the rate of dissolving decreasesgreatly

4. agitation or stirring

stirring distributes the dissolved solute rapidlythrough the solution, and more solvent is broughtinto contact with the solid, causing it to dissolvemore rapidly

17 g

25 g

27 g29 g 30 g


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14.5 Solutions: a reaction medium14.5 Solutions: a reaction mediummany solids must be put into solution to undergoappreciable chemical reaction

ex. NaCl + AgNO 3 AgCl + NaNO 3mixing solid NaCl and solid AgNO 3if any reaction occurs, it is slow and virtually undetctableif dissolving NaCl and AgNO

3separately in

water and mixing two solutions, white AgCl precipitate immediately forms

NaCl (aq) + AgNO 3(aq)AgCl(aq) + Na NO 3(aq)

the mixture of the two solutions provides a

medium or space in which Ag+

and Cl-

reactsolutions also function as diluting agents inreactions in which the undiluted reactants wouldcombine with each other too violently


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14.6 Concentration of solutions14.6 Concentration of solutionsthe concentration of a solution expresses theamount of solute dissolved in a given quantity ofsolvent or solution qualitative expression

dilute solution a solution that contains arelatively small amount of dissolved solute

concentrated solution contains a relativelylarge amount of dissolved solute mass percent solution

ex. 10% NaOH solutiong solute

mass percent = 100g solution

g solute= 100

g solute + g solvent

g soluteparts per million = 1,000,000

(ppm) g solutionex. 14.2 what is the mass percent of NaOH in a

solution made by dissolving 8 g NaOHin 50 g H 2O?

8 100 = 13.8% NaOH solution

50 + 8


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ex. 14.3 what mass of KCl and H 2O are needed to make 250 g of 5% solution?

(250 g) 5% = 12.5 g KCl250 - 12.5 = 237.5 g H 2O

ex. 14.4 a 34% H 2SO 4 solution has a density of 1.25 g/mL, how many g of H 2SO 4 arecontained in 1 L of this solution?

1000 mL

1.25 g/mL = 1250 g solution1250 34% = 425 g H 2SO 4 mass/volume percent (m/V)

gram of solute per 100 mL of solutiong solute

mass/volume percent = 100mL solution

ex. 14.5 a 3% H 2O2 solution, what volume ofthis solution will contain 10 g of H 2O2?

(10 g) / (0.03 g/mL) = 333 mL volume percent

volume of liquid in questionvolume percent = 100

total volume of solution

volume percent is used to express theconcentration of alcohol in beverages


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molarity1000 g of 10% NaOH solution 100 g NaOH1000 g of 10% KOH solution 100 g KOH

mol NaOH = 100/40.0 = 2.50 molmol KOH = 100/56.11 = 1.78 mol

mass percent does not express the number ofmoles of solute

molarity the number of moles of solute per literof solutionnumber of moles of solute

molarity = M = liter of solution

ex. preparation of a 1 M solution


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molarities of concentrated acids commonly usedin the laboratory:

HCl 12 M HC 2H5O2 17 MHNO 3 16 M H2SO 4 18 M

ex. 14.6 what is the molarity of a solutioncontaining 1.4 mol of acetic acid in250 mL of solution?

1.4 mol/0.25 L = 5.6 M ex. 14.7 what is the molarity of a solution made

by dissolving 2.0 g of KClO 3 in water to make 150 mL of solution?

2 g/122.6 g/mol = 0.109 M

150/1000 Lex. 14.8 how many grams of KOH are required

to prepare 600 mL of 0.45 M KOHsolution0.45 M 0.6 L 56.11g/mol = 15.1 g

ex. 14.9 calculate the number of moles ofHNO 3 in 325 mL of 16 M HNO 3solution16 M 0.325 L = 5.2 mol

ex. 14.10 what volume of 0.25 M solution can be prepared from 16g of K 2CO 3

16/138.2 = 0.116 mol0.116 mol /0.25 M = 0.463 L


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ex. 14.13 how many grams of AgCl will be precipitated by adding sufficient AgNO 3 to

react with 1500 mL of 0.4 M BaCl 2 solution?2AgNO 3 + BaCl 2 2AgCl + Ba(NO 3)21.5 L 0.4 M = 0.6 mol BaCl 20.6 mol 2 143.4 g/mol = 172 g AgCl


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14.714.7 ColligativeColligative properties of solutionsproperties of solutionstwo solutions 1 mole urea and 1 mole sucrose in1 Kg water, both have a freezing point of -1.86 oC,not 0 oCin fact, dissolving 1 mole of any nonionizablesolute in 1 Kg of water, the freezing point is-1.86 oCfreezing point depression is a general property ofsolutions, each solvent shows a characteristicfreezing point depression constant

the solution formed by addition of a nonvolatilesolute to a solvent has a lower freezing point , ahigher boiling point , a lower vapor pressure thanthat of pure solventcolligative proerties the properties that depend

only on the number of solute particles in asolution and not on the nature of those particles


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vapor pressure curve of pure water and watersolution

boiling point elevation freezing point depression

some particular applications involving colligative properties:1. use of salt-ice mixture to provide low freezing

temperatures for homemade ice cream2. use of NaCl or CaCl 2 to melt ice from street


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3. use of ethylene glycol-water mixtures asantifreeze in automobile radiators

molality (m) the number of moles of solute perkilogram of solvent

mole of solute m =

Kg solventthe colligative properties

t f = m K f t b = m K bm: molality t f : freezing point depression tb: boiling point elevation

f : freezing point depression constant b : boiling point elevation constant

ex. 14.14 what is the molality of a solution prepared by dissolving 2.7 g CH 3OH in25 g H 2O?

2.7 / 32.04 = 0.084 mol CH 3OH0.084 mol / 0.025 kg = 3.37 m

ex. 14.15 a solution is made by dissolving 100 gethylene glycol in 200 g H 2O, what isthe freezing point of the solution?

100 / 62.07 = 1.61 mol C 2H6O21.61 mol / 0.2 kg = 8.05 m1.86 8.05 = 15 oCfreezing point is -15 oC


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ex. 14.16 a solution is made by dissolving4.71 g of a compound of unknown

molar mass in 100 g H 2O has afreezing point of -1.46 oC, what isthe molar mass of the compound?

t f = 1.46 oC1.46 / 1.86 = 0.785 m0.78 m 0.1 kg = 0.0785 mol

4.71 / 0.0785 = 60.0 g/mol


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14.8 Osmosis and osmotic pressure14.8 Osmosis and osmotic pressurethe red blood cells are enclosed in semipermeablemembranes , they behave differently in the solutionsof different salt concentrations

(a) in an isotonic solution (b) in a hypertonic solution (c) in a hypotonic solution(0.9% saline) (1.6% saline) (0.2% saline)

* 0.9% (0.15 M) NaCl solution is known as physiological saline solution which isisotonic with the blood plasma

a semipermeable membrane allows the passage ofwater (solvent) molecules through it in eitherdirection but prevents the passage of larger solutemolecules or ions

when two solutions of different concentrations areseparated by a semipermeable membrane, waterdiffuses through the membrane from the solution oflower concentration to higher concentrationthis phenomenon is called osmosisall solutions exhibit osmotic pressure which is a

colligative property


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the osmotic pressure can be measured bydetermining the amount of counterpressureneeded to prevent osmosisthe osmotic pressure of a solution containing 1mol of solute particles in 1 kg of water is about22.4 atmdemonstration of osmosis

general chemistry-chapter 14

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