SOLUTION SOLUTION STOICHIOMETRYSTOICHIOMETRY

Part 1aPart 1a

Unit 2 Chapter 4Unit 2 Chapter 41

SolutionsSolutions

A solution is homogenous mixture of 2 or more pure substances

Solvent: most abundant substance in a solution (water is the universal solvent because of strong polar bonds and bent shape)

Solute: all other substances present

Water

• Called the “universal solvent”

• Bent shape (angle = 105)

• O – H bonds are polar covalent resulting from the more electronegative O atom attracting the electrons toward itself

• The O is partially negative while the H’s are partially positive

Dissociation

• When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them.

• This process is called dissociation.

Dissociation

• An electrolyte is a substances that dissociates into ions when dissolved in water and produces a solution that can conduct electricity.

Electrolytes

• A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so.

Electrolytes and Nonelectrolytes

Soluble ionic compounds tend to be electrolytes.

Electrolytes and Nonelectrolytes

Molecular compounds tend to be nonelectrolytes, except for acids and bases.

Electrolytes

• A strong electrolyte dissociates completely when dissolved in water.

• A weak electrolyte only dissociates partially when dissolved in water.

Strong Electrolytes Are…

• HCl H+ + Cl – • 100 molecules of HCl yields ?

• Strong acids• Strong bases

Strong Electrolytes Are…

• Strong acids• Strong bases• Soluble ionic salts

Molarity• Two solutions can contain the same

compounds but be quite different because the proportions of those compounds are different.

• Molarity is one way to measure the concentration of a solution.

moles of solute

volume of solution in litersMolarity (M) =

Molarity

• Example 1: a chemist makes a 400 mL solution by adding 67.4 g of AgNO3 to some water. What is the molarity of this solution?– Step 1 – convert from grams to moles

33

33 AgNO mol 0.3965

AgNO g 170

AgNO molAgNO g 67.4

Molarity

• Example 1: a chemist makes a 400 mL solution by adding 67.4 g of AgNO3 to some water. What is the molarity of this solution?– Step 2 – calculate molarity

33 AgNO M 1

solution L 0.4

AgNO mol 0.3965

Molarity

• Example 2: how many moles of a solute are present in 34 mL of 3.64 M Ba(OH)2?

2OHBa mol 0.090L 0.034M 3.64

VMnV

nM

Molarity• Calculate the molarity of a solution by dissolving 11.5 grams of

solid NaOH in enough water to make 1500 mL of solution.

• Give the concentration of each type of ion in the following solutionsl:– 0.5 M Co(NO3)2

– 1.0 M Fe(ClO4) 3

• Typical blood serum is about 0.14 M NaCl. What volume of blood contains 1.0 mg NaCl?

Mixing a Solution• To create a solution of a

known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute.

• The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask.

How would you do this?

• How would I make 1.00 L of an aqueous 0.200 M K2Cr2O7 solution

– 1. – 2.– 3.– 4.

Dilution of stock solutions• One can also dilute a more concentrated

solution by– Using a pipet to deliver a volume of the solution to

a new volumetric flask, and– Adding solvent to the line on the neck of the new

flask.

DilutionThe molarity of the new solution can be determined from the equation

Mc Vc = Md Vd,

where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions.

Making Dilutions

• Example: Suzie needs 3L of a 0.05M HCl. She only has 12M HCl available. How much does she need to dilute to make her solution?

mL 10L 0.01V

V12M3L0.05M

VMVM

2

2

2211

How would you do this?

• How would I prepare 500 mL of 1.00 M acetic acid from a 17.4 M solution– 1. – 2.– 3.– 4.

Classifying Chemical ReactionsClassifying Chemical Reactions

• SynthesisSynthesis

• DecompositionDecomposition

• Single replacementSingle replacement

• Double ReplacementDouble Replacement

• CombustionCombustion

SynthesisSynthesis

• Two or more substances react to form Two or more substances react to form ONE productONE product

A + B A + B AB AB

SynthesisSynthesis

• Reaction of two elementsReaction of two elements

___Al + ___Cl2 ___AlCl3

Al3+ Cl1-

22 2233

DecompositionDecomposition

• One substance breaks down into two One substance breaks down into two or more simpler productsor more simpler products

AB AB A + B A + B

DecompositionDecomposition

__ NaN3 (s) ___ Na (s) + ___ N2 (g)2 2 3

__ CaO (s) ___ Ca (s) + ___ O2 (g)2 2

Single Replacement ReactionsSingle Replacement Reactions

• One element replaces another One element replaces another element in a compound to form a new element in a compound to form a new compound and elementcompound and element

A + BX A + BX AX + BAX + B

Reactivity SeriesReactivity Series

• MetalsMetals

• A more reactive metal will replace a A more reactive metal will replace a less reactive metal in a solutionless reactive metal in a solution

Li K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Au

most active least active

examplesexamples

• aluminum + iron (III) oxidealuminum + iron (III) oxide

Al Fe2O3+

More reactive?

Al3+ O2-

Al2O3Fe +

Fe3+ O2-

2 2

examplesexamples

• silver + copper (I) nitratesilver + copper (I) nitrate

Ag CuNO3+

More reactive?

Cu1+ NO31-

NO RXN

Double ReplacementDouble Replacement

• Exchange of Exchange of cationscations between two ionic between two ionic compoundscompounds

A B + C D AD + CBswitch

Will the Solutions React?Will the Solutions React?

• One of the following things must One of the following things must occur for a reaction to occur:occur for a reaction to occur:–Precipitate is produced [(Precipitate is produced [(ss) or () or ()])]–Gas is evolved [(Gas is evolved [(gg) or () or ()])]–Water is made [(Water is made [(ll) or () or (gg)])]

• Use the solubility table to Use the solubility table to determine if a solid is madedetermine if a solid is made

Example ProblemExample Problem

• Lithium iodide and aqueous silver nitrate Lithium iodide and aqueous silver nitrate reactreact

Li1+ I1- Ag1+ NO31-

LiI AgNO3 LiNO3AgI+ +(aq)

Use a solubility table to determine state of each component.

(aq) (s) (aq)

CombustionCombustion

• Compound reacts with OCompound reacts with O22

• HydrocarbonHydrocarbon – compound with only – compound with only carbon and hydrogencarbon and hydrogen

CombustionCombustion

• Combustion of hydrocarbonsCombustion of hydrocarbons

ALWAYS produces ALWAYS produces COCO22 and and HH22OO

CxHy + O2 CO2 + H2O

Example ProblemExample Problem

• Show combustion of propane (CShow combustion of propane (C33HH88) gas) gas

C3H8 O2 CO2 H2O+ +5 3 4