Solutions and Solubility Teacher Blog

7/25/2019 Solutions and Solubility Teacher Blog

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Chemistry

30

Unit 5:Solutions and

Solubility

TEACHER


2/20

Components of a Solution

A solution is composed of two or more pure substances mixed togeter! one ofwic is a sol"ent and te oter a solute#

A cup of instant co$ee is te solution! te ot water is te sol"ent! and teinstant co$ee is te solute#

A saturated solution is a solution tat contains te maximum amount of solute

dissol"ed in a sol"ent# A supersaturated solution is a solution were conditionsa"e been canged to allow more solute to dissol"e tan would at roomtemperature %tis is done by eating te sol"ent or solution

'en te sol"ent and solutes are li(uids we can use te terms miscible and

immiscible# )iscible means tat te two li(uids will mix togeter! and

immiscible means tat te two li(uids will not dissol"e in one anoter#

Remember! te sol"ent and solute can be solid! li(uid OR gas# Tere arespecial names for solutions were te solute and sol"ent are bot solids and

wen te solute is a li(uid! and te sol"ent is a solid#o Solid*in*solid + alloys %e#g#! brass , -inc . copper! sterling sil"er , sil"er

. copper

o /i(uid*in*solid + amalgams %e#g#! older dental 0llings , mercury . sil"er

1actors tat may a$ect solubility are temperature and pressure:

o Temperature: 2ases: Temp 3! solubility 4

Solids and li(uids: Temp 3! solubility 3

o ressure: 2ases: ressure 3! solubility 3

Solids and li(uids: una$ected

/i6e dissol"es li6e# Tat is polar co"alent molecules usually dissol"e in oterpolar co"alent molecules and non*polar co"alent molecules dissol"e in non*polar co"alent molecules#

RECALL: Polarity can be determined by subtracting electronegativities. A polarmolecule is one where one (or more) atom in the molecule has a stronger pull on theelectrons than another atom so the electrons move closer to the atom with thestronger pull (higher electronegativity). !his creates a dipole where the atom with the

stronger pull has a slightly negative charge and the atom with the lowerelectronegativity (less pull) has a slightly positive charge.


3/20

Water as a Solvent:

Solutions in wic water iste sol"ent are calleda(ueous solutions#

)ost co"alent li(uids are

only able to dissol"e oterco"alent compounds7 watercan dissol"e bot ionic andco"alent compounds#

Te attraction of water dipoles for ions pulls ions out of a crystalline lattice and intoa(ueous solution#

Aqueous Solutions:

Sometimes wen we mix two dissol"ed salts togeter! we end up wit aprecipitate# Tis is because a new ionic compound is formed tat is insoluble inwater#

We can use solubility charts or solubility tables to determine if a solidwill be formed.

Ion Solubility Exceptions89+ soluble noneCl9;+ soluble noneCl+ soluble except Ag.! Hg


4/20

Calcium Carbonate is insoluble so a precipitate will 'orm sodium nitrate is soluble

See Components of Solutions Assign

Concentration

Concentration refers to te amount of solute dissol"ed in a speci0c amount ofsol"ent#

Concentrated and dilute are (ualitati"e terms we use to describe concentration#

Bilute means tere is not a lot of solute in te solution and concentrated meanstere is a lot of solute in te solution#

Common concentrations are molarity! molality! ppm! and ppb#

olarity

Tis is the number o' moles o' solute dissolved in one litre o' solution#

Te formula for molarity is as follows:

c

n

V

n , moles of solute

D , "olume of solution in litres

c , concentration in moles per litre %)&

Ex. >f a teaspoon %5#m/& of a #5 ) solution of 8aCl was e"aporated! ow manymoles of sodium cloride would be left 'at mass of 8aCl would be left

c=n

Vn=cV

n=(0.50M) (0.0050L ) *.**#+ mol

convertmass :0.0025mol x58.4428g

1mol =0.15g

Ex. Antifree-e is a solution of etylene glycol! C

)oles of C


5/20

A standard solution is a solution of a 6nown concentration# Tis means it as aprecise mass of solute in a speci0c "olume of solution#

Standard solutions are used in experiments were te concentration of a solutionmust be 6nown#

'e use "olumetric Kas6s to prepare standard solutions as tey a"e a smallmargin of error wen compared to oter pieces of lab e(uipment# DolumetricKas6s come in a "ariety of si-es %"olumes

To prepare a standard solution we follow the following steps:

# Calculate te re(uired mass of solute needed using te "olume and concentrationyou want to end up wit#


6/20

Ex.'ater is added to


7/20

Ex. 'at are te concentrations of te ions in an a(ueous solution containing #5molJ/ iron%>>>& nitrate

1e%89&%s&

1e.%a(&. 89O%a(&

M1e.N , #5 molJ/ 1e%89&G

3

3 3

1

1 ( )

mol Fe

mol Fe NO

+

, #5 molJ/ 1e.

M89ON , #5 molJ/ 1e%89&G

3

3 3

3

1 ( )

mol NO

mol Fe NO

, #;5 molJ/ 89O

Ex.


8/20

1or example te allowable concentration of mercury in air is L


9/20

See Concentration an! "ilution Assignment

%&e Solubility #ro!uct Constant:

All salts a"e di$erent solubilities# E"en insoluble salts will dissol"e in water tosome extent#

'en a salt is dissol"ed in water! some of te salt dissol"es and some may not#Te amount of salt tat dissociates into ions is di$erent for e"ery salt#

@spis a number tat represents ow muc of te salt will dissociate into ions#

@spis e(ual to te product of te concentration terms eac raised to te power ofte coecients of te substance in te dissociation e(uation#

@sp"alues f te @spis low! te solid is not "ery soluble#

o >f te @spis ig! te solid is soluble#

An expression for te solubility product constant! Ksp! of calcium pospate would be asfollows:

?alanced E(uation: Ca%9;&


10/20

1.6102g

1L

1mol

78.1g=2.010

4M , x

1ind @sp using solubility constant expression:

@sp , MCa


11/20

Solubility #ro!uct Constants near '( oC

)ormula * spAl%9H& #G+

Al9; F#G+X

?aC9 5#G+X

?aCr9; #


12/20

1e;M1e%C8&FN

#G+;

1e%9H& ;G+L

1e9; #G+


13/20

Ag


14/20

= Sul0de e(uilibrium of te type:

)S%s& . H


15/20

c,

n

V

M)gC9N ,

-31.4 10 mol

10.0 L, #; G *;molJ/

i' 5;gC$7 2.8 < 2*98mol=L then 5;g#&7 and 5 C$

#97 each 2.8 < 2*98mol=L

@sp, %#; G *;&%#; G *;&

-sp, %#; G *;&


16/20

copper ions %te common ion& tings will cange# /etWs say we added someiodide ions7 tis will increase te concentration of iodide and te product of tecopper ions and iodide ions would be iger tan te @sp "alue# Tis is notpossible so te concentrations would need to be lowered# >n order to lower teconcentration of iodide ions! some copper %>& iodide would need to precipitateout# Tis follows /e CatelierWs rinciple because we increased te concentrationof te products %iodide ions& so te reaction sifts to te reactants#

After adding iodide ions to te solution! copper %>& iodide will precipitate out! but

once te reaction reaces e(uilibrium again! te concentration of copper ionsand iodide will no longer be e(ual %tere will be more iodide ions in solution tancopper ions Tis also means te concentration of Cu.will be lower tan at teoriginal e(uilibrium and te concentration of > *will be iger tan at te originale(uilibrium#

Overvie,:>f a sligtly soluble ionic compound is dissol"ed in water! you canforce precipitation of tat salt by adding a readily soluble ionic compound tatas an ion in common wit te sligtly soluble salt# Tis sift is 6nown as tecommon ion e+ect#

&%.!e -spof sil"er iodide is

178.3 10# 'at is te iodide ion concentration of a # /

saturated solution of Ag> to wic #%a(& V Ag.%a(& . >*%a(& -sp,

[ ][ ]Ag I+ = 178.3 10

>f te e(uilibrium concentration of iodide ion from te dissociation is%! ten tee(uilibrium concentration of sil"er ion is%. #


17/20

To calculate selecti"e precipitation we use initial concentrations %\&! instead of tee(uilibrium concentrations#

>n selecti"e precipitation tere are restraints in forming a precipitate7 a precipitatedoesn]t always form in a solution# >t depends on te relationsip between @ and \:

o >f \^@ a precipitate formsand te reaction proceeds to te left

o >f \_@ no precipitate formsand te reaction proceeds to te rigt

o

>f \,@ te reaction is at e(uilibrium

Example:>f ;/ of #5) @Cl is mixed wit F/ of #) b%89 &


18/20

precipitate 0rst 'ic will be in excess

>irst we plug the given values into the -sp epression 'or bCl


19/20

-ab: Analying for Anions

#/R#OSE

>n tis experiment you will obser"e and record some caracteristic cemical reactionsof se"eral negati"ely carged ions: S9;


20/20

#ROCE"/RE

a# Te tests can easily be made by putting a few drops of a solution on a plastic 0lmand adding to tis a few drops of one of te reagents# B9 89T use te tip of a dropperfrom a stoc6 bottle for stirring# Boing so could contaminate te solution contained inte bottle# Use a tin glass rod#

b# Test

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