5. Bonding and Intermolecular Forces · 3 of 43 © Boardworks Ltd 2009 Solubility Chemistry: Terms...

1 of 43 © Boardworks Ltd 2009

Chemistry 11

Solution Chemistry


Crash Course: Solutions

https://www.youtube.com/watch?v=9h2f1Bjr0p4&t=39s


Solubility Chemistry: Terms

Solution:

• a homogeneous mixture of two or more

substances

• a mixture of two or

more different types

of particles that looks

like one substance

• ex: salt water,

koolaid


Solvent vs Solute

The Solvent is the most abundant

component of a solution

The Solute is the component(s) that

are less abundant

In salt water:

Solvent: water Solute: salt

In KoolAid:

Solvent: water Solutes: sugar, KoolAid crystals


Symbols

The symbol (aq) after a formula – stands

for aqueous.

This indicates a solution that has water as

the solvent

ex. NaCl(aq) means “NaCl dissolved in water”


Types of Solutions

Solutions can be:

· liquid – solid

salt water, KoolAid

· gas – gas

· air

· liquid – liquid

water and vinegar

· liquid – gas

pop

· solid – solid

metal alloys: bronze,steel, brass


What happens when NaCl dissolves?

• Water molecules

(solvent) collide with

salt crystals (solute),

which are in a crystal

lattice, knocking Na+

and Cl ions off the

crystal and into the

water.

• Eventually, the crystal is

gone and all the ions

are dispersed among

the water molecules.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf


What happens when NaCl dissolves?

• Because the crystal has been dispersed into

individual ions, you can no longer see the salt

in the water, and the result is a homogeneous

mixture… a solution!

• The ions are surrounded by water molecules

(called hydration shells) as seen below.


Temperature and Solutions

• Higher temperature makes

the water molecules move

faster and collide with the

crystal lattice harder and

more often

• Thus, a higher temperature

speeds up dissolving.

• A higher temperature also

increases the amount of

solute that will dissolve.


Saturated Solutions

• When a solution is

saturated, it has the

maximum amount of

solute possible for a

given amount of

solvent

• Saturated solutions

have excess solute

remaining on the

bottom of the

container as no more

can dissolve


Saturated Solutions

Two processes are occurring in saturated solutions:

1. solute crystals are dissolving

2. the ions already dissolved in solution are “recrystallizing”

These two processes happen at the same rate.

• Dissolving: NaCl(s) Na+(aq) + Cl(aq)

• Recrystallizing: Na+(aq) + Cl(aq) NaCl(s)

•These two processes are opposites, and since they occur at the

same rate, no net change results!


Concentration

• The concentration of a solution is the amount of solute in a

given volume of solution

• If there is a lot of solute in a solution, the solution is

concentrated.

• If there is a little solute in a solution, the solution is dilute.

• The amount of solute is usually measured in grams or moles

the volume of solvent is usually measured in L or mL


Remember…


Making Solutions

How many moles of NaCl are needed to

make 6.0 L of a 0.75 M NaCl solution?

Moles = Molarity x Volume

= 0.75 M x 6.0 L

= 4.5 mol


Quick Reminder:

A salt is an ionic compound made up of a metal cation and a

nonmetal anion

Salts dissolve in a process called “dissociation”

• This means that the compound not only dissolves, but it 'dissociates'

into ions.

• e.g. KCl(s) K+(aq) + Cl(aq)

Every salt dissolves in water to some extent.

The amount of salt required to saturate the solution depends on the

type of salt.

Some salts can have a very high molarity before they become

saturated, and some become saturated at very low molarities.

If a salt has a saturated solution concentration greater than 0.1M, it

is said to be soluble.

If less than 0.1M, it is said to be low solubility


Dissociation Equations for Salts

LiF(s) Li+ (aq) + F(aq)

MgI2(s) Mg2+(aq) + 2I(aq)

· (note: 2 iodide ions!)

Na2SO4(s) 2Na+(aq) + SO42-(aq)

(NH4)2CO3 2NH4+(aq) + CO3

2-(aq)

Remember: Polyatomic compounds are also

ionic in nature!


Dissociation Equations/Ion

Concentrations Worksheet


Covalent Compounds

Covalent molecules have partial charges (if polar) or no

charges (nonpolar)

If a covalent compound can dissolve in water, it must be

polar, and it dissolves as a whole molecule (it doesn't

dissociate into ions).

e.g. Sugar C12H22O11(s) C12H22O11(aq)


Acid Solubility

Acids dissolve by reacting with water to form ions

(see p. 74 HEBDEN for all acids)

Strong partial negative dipole on O from H2O removes

H+ from acid

E.g. Hydrochloric acid


Hebden

pg 194 #1-4

Pg 210 #28

Dissociation Equations/Ion

Concentrations Worksheet


Polar & Non-Polar Molecules


What determines Solubility?

“Like Dissolves

Like” Rule

Substances with charges (full or partial) like to mix with one another.

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

http://www.scienceprofonline.com/virtual-cell-main.html

http://www.scienceprofonline.com/


“Like Dissolves Like”

• Polar or ionic solutes tend

to dissolve in polar

solvents

Case Study 1: NaCl

• Nonpolar solutes tend to

dissolve in non polar

solvents

Case Study 4: Iodine in

Carbon Tetrachloride


Water dissolves more substances than any other liquid.

The water molecule’s polarity makes it such an excellent solvent.

The polarity allows water to become attracted to many other charged (ions) or partially charged (polar) molecules.

Case study 2

Water is considered the “Universal Solvent”


Polar vs Non-polar Covalent Bonds

Polar molecules unequally share electrons between atoms, so have a

slight positive charge at one end and a slight negative charge at the other.

Non-polar molecules have electrons equally shared

between their atoms.


Water: The Universal Solvent

Water is a good solvent for many other polar solutes.

Polar Covalent Molecules include:

• Ammonia NH3

• Glucose C6H12O6

• Urea (NH2)2CO

*High ratio of O’s and N’s tend to make a molecule polar.

For example, blood is a water based solution.


Water is also a good solvent for ionic compounds. (a.k.a. salts & electrolytes)

The partial and full charges attract each other.

Salts dissociate into their ions in water.

Video of dissociation of NaCl into water.

Video clip from movie Idiocracy: “Brawndo Has What Plants

Crave!”



http://www.youtube.com/watch?v=EBfGcTAJF4o

https://www.youtube.com/watch?v=-Vw2CrY9Igs




Charged molecules are Hydrophilic

- from the Greek (hydros)

"water" and (philia)

"friendship”

- Water loving

- Water soluble

- Example: Water & sugar



Non-polar substances DO NOT carry any kind of charge

Mainly molecules made of C’s and H’s.

Example: Oily or gasoline based substances


Water: The Universal Solvent…or is it?




Oil and Water Don’t Mix

• Oil is nonpolar

• Water is polar

“Like dissolves like”

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 470


Non-polar, uncharged molecules are Hydrophobic

• from the Greek (hydros) “water” and (phobia) “fearing” or “hating”

• Water-fearing• Not water soluble• Example: Cholesterol is not water soluble

Non-polar solvents dissolve non-polar solutes.

Examples: • Turpentine dissolves oil-based paints.• Cholesterol is important component of greasy cell membranes.

“Like Dissolves Like”


Hebden

pg 205 #17

Pg 207 #18-22

198 #6-8


Conductivity

Conductivity is dependent on charged particles

• Ionic solutions conduct very well because charged particles (ions)

are present

• Acid solutions conduct very well because ions are present

• Covalent solutions do not conduct electricity because no charges

are present (entire neutral molecules are dissolved)

• The more ions in the solution, the greater the conductivity

• Therefore concentrated solutions conduct better than dilute

solutions


Solubility & Precipitation

Remember that EVERY salt dissociates to some extent

in water.

Some salts dissociate a great amount and have a high

molarity at saturation, while others become saturated at

a very low molarity.

A 'soluble' salt has a saturation molarity greater than

0.10M, whereas a 'low solubility' salt becomes saturated

at a molarity lower than 0.10M.


The Solubility Table

Allows us to

determine which

salts are 'soluble'

and which are 'low

solubility'


How to use the Solubility Table

Use your table to predict whether the following salts are soluble

(S) or low solubility (LS) and whether they form a precipitate

(ppt) in water.

NaOH S

NH4CH3CO2 S

CaSO4 LS (form ppt)

PbCl2 LS (form ppt)

KCl S

CaBr S

K2CO3 S

Al2(SO4)3 S

CuCl2 S

CuCl LS (form ppt)


Practice Question

Suppose you wanted to make a saturated solution of PbI2.

One way you could do this is to dissolve (dissociate) PbI2 in

water (making Pb2+(aq) and I(aq)) until no more will dissolve and

you have excess PbI2(s) on the bottom.

Another way is to mix one solution that has Pb2+(aq) ions to

another solution that has I(aq) ions….


http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf

http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf


Double Displacement Reactions (revisited)

Let`s suppose you decided to mix equal volumes of two soluble salt

solutions together, such as 0.20M KI(aq) with 0.20M Pb(NO3)2(aq)

KI(aq) is actually K+(aq) and I( aq) Pb(NO3)2 (aq) is actually Pb2+(aq) and NO3(aq)

By mixing, you`ve introduced Pb2+ to I- and also K+ to NO3-.

If either of these combinations are `low solubility` together, they will be

'oversaturated' and precipitate out of solution (form a solid).

This will be the case for Pb2+ and I and they will form the precipitate

PbI2(s), thereby creating a saturated solution of PbI2.

In this case, K+ and NO3- are ‘spectator ions’, meaning they do not

participate directly in the reaction


Precipitation Reactions

When two soluble ionic solutions that have molarities

greater than 0.10M are mixed together and at least one new

combination of cation and anion have low solubility, a

precipitate forms.

As we know, Pb2+ and I are low solubility together, so when

mixed together, they will precipitate out of solution.

The saturation molarity for PbI2 is 000137M, so solid PbI2 will

precipitate out until that molarity remains in solution as

aqueous ions


0.10M I-0.10M Pb2+

0.00137M

Pb2+ and I-

ions remain

The rest

precipitates

out as solid

PbI2


Practice Question:

Metals will swap

Calculate ionic charges to determine chemical

formula of products

Check solubility table to determine if a ppt is

formed


Practice Question:

K2CrO4(aq) + Ba(NO3)2 (aq) → what are the products?

The ions in solution are:

K+ CrO42- Ba2+ NO3-

So what (if any) will form a precipitate?

BaCrO4 + KNO3


Mixing Ionic Solutions

When mixing two ionic solutions three

outcomes can result:

• No precipitate forms (all combinations of cation & anion are

soluble)

• One precipitate forms (one combination of cation & anion

have low solubility)

• Two precipitates form (both combinations of cation and

anion have low solubility)


Practice Question

What would result if 1.0M solutions of

Al2(SO4)3(aq) and Sr(OH)2(aq) were mixed

together?

The products would be:

Al(OH)3(s) and SrSO4(s)

This is a 2 precipitate reaction


Practice Questions: Separating Ions from Solution Worksheet

Remember: Add a cation as a nitrate salt to precipitate an anion. Add an

anion as a sodium salt to precipitate a cation.

1. Construct a flowchart to separate solutions that contain one or

more of each of the following ions.

a) SO42-

and PO43-

b) Pb2+

and Ba2+

c) Fe2+

, Pb2+

, and Mg2+

d) Br-, CO3

2-, and SO4

2-

e) SO42-

, S2-

, and OH-


Using the Solubility Table

Worksheet

5. Bonding and Intermolecular Forces · 3 of 43 © Boardworks Ltd 2009 Solubility Chemistry: Terms...

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