Ch 17sec3

17.317.3

Aqueous SolutionsAqueous Solutions

1. What is the difference between molecular and ionic compounds?

2. What is a cation?

3. What is an anion?

4. Why are ionic compounds generally soluble in water?

Aqueous SolutionsAqueous Solutions A solution is a homogenous mixture- it is A solution is a homogenous mixture- it is

stable; parts cannot be separated by stable; parts cannot be separated by filtering; one phasefiltering; one phase

Solutions have two parts: Solutions have two parts: Solute and Solute and solventsolvent

SoluteSolute- substance that gets dissolved- substance that gets dissolved SolventSolvent- substance that does the dissolving- substance that does the dissolving Solutions with water as the solvent are Solutions with water as the solvent are

calledcalled aqueous solutions aqueous solutions Solvents and solutes can be solids, liquids Solvents and solutes can be solids, liquids

or gassesor gasses

ExamplesExamplesSolutionSolution SoluteSolute SolventSolvent

saltwatersaltwater saltsalt waterwater

bloodblood NaNa++, K, K++,, CaCa+2+2,,

OO2, 2, COCO22

waterwater

airair OO2, 2, COCO22, H, H22O,O, NN22

Notice- you can have more than one solute; usually the solvent is the substance in the greatest amount

Aqueous SolutionsAqueous Solutions

In aqueous solutions the solutes are In aqueous solutions the solutes are usually ionic and/or polar covalent usually ionic and/or polar covalent compounds ( remember water itself compounds ( remember water itself is polar)is polar)

““Like dissolves Like” this means Like dissolves Like” this means polar substances dissolve in polar polar substances dissolve in polar substances and nonpolar substances substances and nonpolar substances dissolve in nonpolar substancesdissolve in nonpolar substances

Which of the following would dissolve in water?

A) Oil

B) CH4 (methane)

C) LiCl

D) I2

Which of the following would not dissolve in water?

A) He

B) MgSO4

C) NaHCO3

D) KCl

True or False

In a saltwater solution the salt is the solvent.

Solution ProcessSolution Process SolvationSolvation- process whereby solutes dissolve- process whereby solutes dissolve In ionic compounds- the + ions are In ionic compounds- the + ions are

surrounded by the negative end of the water surrounded by the negative end of the water molecule (O), and the – ions are surrounded molecule (O), and the – ions are surrounded by the + end of the water molecule (H)- thus by the + end of the water molecule (H)- thus separating the ions from each otherseparating the ions from each other

Not all ionic compounds will dissolve- some Not all ionic compounds will dissolve- some have such a strong attraction to their ions have such a strong attraction to their ions they are said to be insoluble ( reference they are said to be insoluble ( reference table) table)

Which substance will not dissolve in water ( use solubility chart)?

A) KF

B) NH4Cl

C) Pb(OH)2

D) CaCl2

Solvation continuedSolvation continued In molecular (covalently bonded) substances In molecular (covalently bonded) substances

the + end of a polar solute will be attracted the + end of a polar solute will be attracted to the – end of the water molecule, and the – to the – end of the water molecule, and the – end of the polar solute will be attracted to end of the polar solute will be attracted to the –end of the water molecule so dissolving the –end of the water molecule so dissolving takes place ; polar substances dissolve in takes place ; polar substances dissolve in polar substances-Like dissolves Likepolar substances-Like dissolves Like

Nonpolar substances, like oil will not dissolve Nonpolar substances, like oil will not dissolve in water- there is no + or – end to the in water- there is no + or – end to the nonpolar molecule; but nonpolar will dissolve nonpolar molecule; but nonpolar will dissolve in nonpolar substances- Like dissolves Likein nonpolar substances- Like dissolves Like

Simulation 19Simulation 19

ElectrolytesElectrolytes

Substances that conduct electricity in its Substances that conduct electricity in its aqueous or molten form are called aqueous or molten form are called electrolyteselectrolytes

Ionic compounds are electrolytes Ionic compounds are electrolytes ifif they they are soluble in water ( NaCl- yes; BaSOare soluble in water ( NaCl- yes; BaSO44--no, insoluble)no, insoluble)

Compounds that do not conduct Compounds that do not conduct electricity in either the molten state or in electricity in either the molten state or in aqueous form are called aqueous form are called nonelectrolytesnonelectrolytes

Solution of solidsSolution of solids While covalent compounds do not dissociate, While covalent compounds do not dissociate,

they are solvated in solution.they are solvated in solution.

Electrolytes continuedElectrolytes continued

Most molecular compounds are Most molecular compounds are nonelectrolytesnonelectrolytes

A few A few very polarvery polar molecular compounds molecular compounds however will ionize in solution and so however will ionize in solution and so are electrolytes( HCl, NHare electrolytes( HCl, NH3,3,) when they ) when they are dissolved in waterare dissolved in water

HClHCl(g) (g) + H+ H2200(l) (l) HH33OO++(aq)(aq) + Cl + Cl--

(aq) (aq)

Simulation 20 Simulation 20

Electrolytes continuedElectrolytes continued Not all electrolytes conduct electricity to Not all electrolytes conduct electricity to

the same degree- some are better the same degree- some are better conductors than others- there are conductors than others- there are weak weak electrolyteselectrolytes and and strong electrolytesstrong electrolytes

What makes them weak or strong is how What makes them weak or strong is how much many of the ions dissociate ( split up) much many of the ions dissociate ( split up) when in solution. If almost all do, then it is when in solution. If almost all do, then it is a strong electrolyte; if only a few of the ions a strong electrolyte; if only a few of the ions dissociate, then it is a weak electrolyte dissociate, then it is a weak electrolyte ( chart pg 485)( chart pg 485)

Conductivity testers can determine if a Conductivity testers can determine if a substance is an electrolytesubstance is an electrolyte

Strong ElectrolytesStrong Electrolytes Strong, inorganic Strong, inorganic

acidsacids Strong inorganic Strong inorganic

basesbases Soluble salts (ionic Soluble salts (ionic

compounds)compounds)

Weak ElectrolytesWeak Electrolytes

Heavy metal halides ( PbClHeavy metal halides ( PbCl22))

NHNH3 3 (weak base)(weak base) Organic acids and basesOrganic acids and bases HH22OO

NonelectrolytesNonelectrolytes

Most organic compoundsMost organic compounds Nonpolar moleculesNonpolar molecules

Water of HydrationWater of Hydration

When water is an integral part of the When water is an integral part of the crystalline structure of a substance, the crystalline structure of a substance, the water is called the water is called the waterwater of hydrationof hydration

A substance with water of hydration in A substance with water of hydration in it is called a it is called a hydratehydrate

Examples: Examples: CuSOCuSO44..5H5H22OO

MgSOMgSO44..7H7H22O (epsom salt)O (epsom salt)

HydratesHydrates Water in hydrates is not held very tightly Water in hydrates is not held very tightly

and so hydrates tend to have noticable and so hydrates tend to have noticable vapor pressures ( from water leaving the vapor pressures ( from water leaving the crystal)crystal)

If the hydrate’s vapor pressure is higher If the hydrate’s vapor pressure is higher than water vapor pressure, the hydrate than water vapor pressure, the hydrate will will effloresceeffloresce, which means it loses its , which means it loses its water of hydration naturally-this is why water of hydration naturally-this is why some hydrates become coated with a some hydrates become coated with a white powder- it is the anhydrous form white powder- it is the anhydrous form of the compoundof the compound

Hydrates con’tdHydrates con’td Hygroscopic Hygroscopic compounds are hydrates that compounds are hydrates that

remove water from the air- they have a low remove water from the air- they have a low vapor pressurevapor pressure

They are used as They are used as desiccantsdesiccants- they remove - they remove moisture from the air (like from the shoebox of moisture from the air (like from the shoebox of that expensive leather boots you got)that expensive leather boots you got)

DeliquescentDeliquescent compounds are so hygroscopic compounds are so hygroscopic (water loving) they remove enough from water (water loving) they remove enough from water from the air to turn into a solution. This occurs from the air to turn into a solution. This occurs when their vapor pressure is much lower than when their vapor pressure is much lower than water’swater’s

CaClCaCl22..HH22O CaClO CaCl22

..2H2H22OO

% Water in a Hydrate% Water in a Hydrate

You can calculate the % water in a You can calculate the % water in a hydrate similar to % composition hydrate similar to % composition problemsproblems

Mass of Water Mass of Water x 100x 100Total mass of CompoundTotal mass of Compound

ProblemProblem

Find the % by mass of water in Find the % by mass of water in sodium carbonate decahydrate. sodium carbonate decahydrate. ( Na( Na22COCO33

..10H10H22O)O)

10 x 18g/1mol= 180g water10 x 18g/1mol= 180g water

2(23)+12+3(16) +180=286g 2(23)+12+3(16) +180=286g NaNa22COCO33

..10H10H22OO

180g/286 x 100=62.9%180g/286 x 100=62.9%

What is the % water in CuSO4. 5H20

2 sig figs2 sig figs

What is the % water in CaCl2. 6H2O

2 sig figs2 sig figs