ch 4 types of chemical reactions and solution stoichiometry n.
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Ch. 4 Types of Chemical Reactions and Solution Stoichiometry. Solute. A solute is the dissolved substance in a solution. Salt in salt water. Sugar in soda drinks. Carbon dioxide in soda drinks. Solvent. A solvent is the dissolving medium in a solution. Water in salt water.

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solute
Solute

A solute is the dissolved substance in a solution.

Salt in salt water

Sugar in soda drinks

Carbon dioxide in soda drinks

Solvent

A solvent is the dissolving medium in a solution.

Water in salt water

Water in soda

saturation of solutions
Saturation of Solutions
  • A solution that contains the maximum amount of solute that may be dissolved under existing conditions is
    • saturated.
  • A solution that contains less solute than a saturated solution under existing conditions is
    • unsaturated.
  • A solution that contains more dissolved solute than a saturated solution under the same conditions is
    • supersaturated.
definition of electrolytes and nonelectrolytes
Definition of Electrolytes and Nonelectrolytes

An electrolyte is:

  • A substance whose aqueous solution conducts
  • an electric current.

A nonelectrolyte is:

  • A substance whose aqueous solution does not
  • conduct an electric current.

Try to classify the following substances as

electrolytes or nonelectrolytes…

electrolytes
Electrolytes?
  • Pure water
  • Tap water
  • Sugar solution
  • Sodium chloride solution
  • Hydrochloric acid solution
  • Ethyl alcohol solution
  • Pure, solid sodium chloride
answers
Answers…

ELECTROLYTES:

NONELECTROLYTES:

  • Tap water (weak)
  • NaCl solution
  • HCl solution
  • Pure water
  • Sugar solution
  • Ethanol solution
  • Pure, solid NaCl

But why do some compounds conduct electricity in

solution while others do not…?

ionic compoundsdissociate
Ionic CompoundsDissociate

NaCl(s) 

Na+(aq) + Cl-(aq)

AgNO3(s) 

Ag+(aq) + NO3-(aq)

MgCl2(s) 

Mg2+(aq) + 2 Cl-(aq)

Na2SO4(s) 

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

AlCl3(s) 

Al3+(aq) + 3 Cl-(aq)

ions tend to stay in solution where they can conduct a current rather than re forming a solid
Ions tend to stay in solution where they canconduct a current rather than re-forming a solid.

The reason for this is the polar nature of

the water molecule…

Positive ions associate with the negative

end of the water dipole (oxygen).

Negative ions associate with the positive

end of the water dipole (hydrogen).

some covalent compounds ionize in solution
Some covalent compounds IONIZE in solution

Covalent acids form ions in solution, with the

help of the water molecules.

For instance, hydrogen chloride molecules,

which are polar, give up their hydrogens to

water, forming chloride ions (Cl-) and

hydronium ions (H3O+).

strong acids such as hcl are completely 100 ionized in solution
Strong acids such as HCl are completely100% ionized in solution.

Other examples of strong acids include:

  • Sulfuric acid, H2SO4
  • Nitric acid, HNO3
  • Hydriodic acid, HI
  • Perchloric acid, HClO4
weak acids such as lactic acid usually ionize less than 5 of the time
Weak acids such as lactic acid usually ionize less than 5% of the time.

Many of these weaker acids

are “organic” acids

that contain a “carboxyl”

group.

The carboxyl group does not easily give up its

hydrogen.

because of the carboxyl group organic acids are sometimes called carboxylic acids
Because of the carboxyl group, organic acids aresometimes called “carboxylic acids”.

Other organic acids and their sources include:

  • Citric acid – citrus fruit
  • Malic acid – apples
  • Butyric acid – rancid butter
  • Amino acids – protein
  • Nucleic acids – DNA and RNA
  • Ascorbic acid – Vitamin C

This is an enormous group of compounds; these

are only a few examples.

however most covalent compounds do not ionize at all in solution
However, most covalent compounds do not ionizeat all in solution.

Sugar (sucrose – C12H22O11),

and ethanol (ethyl alcohol – C2H5OH) do not

ionize -

That is why they are nonelectrolytes!

molarity
Molarity

The concentration of a solution measured in moles of solute per liter of solution.

M = mol

L

preparation of molar solutions
Preparation of Molar Solutions

Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution?

  • Step #1: Ask “How Much?” (What volume to prepare?)
  • Step #2: Ask “How Strong?” (What molarity?)
  • Step #3: Ask “What does it weigh?” (Molar mass is?)

1.500 L

0.500 mol

58.44 g

= 43.8 g

1 L

1 mol

serial dilution

It is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution.

Serial Dilution

Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution?

MstockVstock = MdiluteVdilute

(11.6 M)(x Liters) = (3.0 M)(0.250 Liters)

x Liters = (3.0 M)(0.250 Liters)

11.6 M

= 0.065 L

a single replacement reactions
A. Single Replacement Reactions

A + BX  AX + B

BX + Y  BY + X

Replacement of:

  • Metals by another metal
  • Hydrogen in an acid by a metal
  • Hydrogen in water by a metal
  • Halogens by more active halogens
  • Ex. Mg(s) + HCl(aq)

MgCl2(aq) + H2(g)

  • Ex. 2 Li(s) + 2 H2O(l)

2 LiOH(aq) + H2(g)

the activity series of the metals
The Activity Series of the Metals
  • Lithium
  • Potassium
  • Calcium
  • Sodium
  • Magnesium
  • Aluminum
  • Zinc
  • Chromium
  • Iron
  • Nickel
  • Lead
  • Hydrogen
  • Bismuth
  • Copper
  • Mercury
  • Silver
  • Platinum
  • Gold

Metals can replace other metals

provided that they are above the

metal that they are trying to

replace.

Metals above hydrogen can

replace hydrogen in acids.

Metals from sodium upward can

replace hydrogen in water

the activity series of the halogens
The Activity Series of the Halogens
  • Fluorine
  • Chlorine
  • Bromine
  • Iodine

Halogens can replace other

halogens in compounds, provided

that they are above the halogen

that they are trying to replace.

2NaCl(s) + F2(g) 

2NaF(s) + Cl2(g)

???

MgCl2(s) + Br2(g) 

No Reaction

???

practice problems answers are unbalanced
Practice problems - Answers are unbalanced! 

1. Mg + FeCl3

Fe + MgCl2

2. Sodium is added to water.

Na + H2O  H2 + NaOH

3. Lithium is added to hydrochloric acid

Li + HCl  H2 + LiCl

4. Zinc is added to a solution of sodium chloride

Zn + NaCl  N.R.

5. Chlorine gas is bubbled into a solution of potassium iodide

Cl2 + KI  I2 + KCl

6. Chlorine gas is bubbled into a solution of potassium fluoride

Cl2 + KF  N. R.

double replacement reactions
Double Replacement Reactions

The ions of two compounds exchange placesin an

aqueous solution to form two new compounds.

AX + BY  AY + BX

One of the compounds formed is usually a

precipitate(an insoluble solid), an insoluble gasthat bubbles out of solution, or a molecular compound, usually water.

slide22

Double replacement forming a precipitate…

Double replacement (ionic) equation

Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq)

Complete ionic equation shows compounds as aqueous ions

Pb2+(aq) + 2 NO3-(aq) + 2 K+(aq) +2 I-(aq)  PbI2(s) + 2K+(aq) + 2 NO3-(aq)

Net ionic equation eliminates the spectator ions

Pb2+(aq) + 2 I-(aq)  PbI2(s)

d r practice problems
D.R. Practice problems

1. KBr(aq) + AgNO3(aq) 

AgBr(s) + KNO3(aq)

2. Silver nitrate + potassium chromate 

2AgNO3(aq) + K2CrO4(aq)  AgCrO4(s) + 2KNO3(aq)

3. Ammonium chloride + cobalt (II) sulfate 

2NH4Cl(aq) + CoSO4(aq)  (NH4)2SO4(aq) + CoCl2(aq) N.R.

4. Lithium hydroxide + sodium chromate

2LiOH(aq) + Na2CrO4(aq)  2NaOH(aq) + Li2CrO4(s)

5. Zinc acetate + cesium hydroxide 

Zn(C2H3O2)2(aq) + 2CsOH(aq)  Zn(OH)2(s) + 2CsC2H3O2(aq)

6. What is the net ionic equation for the rxn above?

Zn+2(aq) + OH-(aq)  Zn(OH)2(s)

unstable compounds own note paper
Unstable Compounds!!! (own note paper)
  • Ammonium hydroxide
    • NH4OH
  • Carbonic Acid
    • H2CO3
  • Sulfurous acid
    • H2SO3
  • Sulfide salts (ex. Na2S) from acid (H+)
  • All break down to form other products!
    • NH4OH  NH3(g) + H2O(l)
    • H2CO3  CO2(g) + H2O(l)
    • H2SO3  SO2(g) + H2O(l)
    • S-2  H2S(g)
unstable examples

1. Sodium sulfite + hydrochloric acid

Unstable Examples:

Na2SO3(aq) + 2HCl(aq)  H2SO3(aq) + 2NaCl(aq)

H2SO3(aq)  H2O(l) + SO2(g)

Na2SO3(aq) + 2HCl(aq)  H2O(l) + SO2(g) + 2NaCl(aq)

2. Ammonium sulfate + sodium hydroxide

(NH4)2SO4(aq) + NaOH(aq)  2 NH4OH(aq) + Na2SO4(aq)

2 NH4OH(aq)  2 NH3(g) + H2O(l)

(NH4)2SO4(aq)+ 2NaOH(aq)  2NH3(g) + 2H2O(l) + Na2SO4(aq)

What is the net ionic equation for the reaction above?

NH4+(aq) + OH-(aq)  NH3(g) + H2O(l)