Post on 02-Feb-2021
MDM. NURUL IFFAH BTE AB HALIM
DEPARTMENT OF ENGINEERING TECHNOLOGY (PLANT MAINTENANCE)
KKTM LENGGONG
Content:4.1 The Mole4.2 Molar Mass4.3 Chemical Equations4.4 Types of Reaction4.5 Oxidation-Reduction Reactions4.6 Stoichiometry
At the end of the topic, student should be able to :
1. Solve the calculations related to mole and molar mass.
2. Demonstrate the chemical equation.
3. Explain the type of chemical reactions.
4. Describe the oxidation and reduction reactions.
5. Perform the stoichiometry calculations.
Create interactive online presentations
Christopher G. Hamaker, Illinois State University, Normal IL
© 2005, Prentice Hall
The Mole
Avogadro’s Number (symbol N) is the number of atoms in 12.01 grams of carbon.
Its numerical value is 6.02 × 1023.
Therefore, a 12.01 g sample of carbon contains 6.02 × 1023
carbon atoms.
The mole (mol) is a unit of measure for an amount of a chemical substance.
A mole is Avogadro’s number of particles, that is 6.02 × 1023
particles.
1 mol = Avogadro’s Number = 6.02 × 1023 units
We can use the mole relationship to convert between the number of particles and the mass of a substance.
First we write down the unit asked for
Second we write down the given value
Third we apply unit factor(s) to convert the given units to the desired units
How many sodium atoms are in 0.120 mol Na?
Step 1: we want atoms of Na
Step 2: we have 0.120 mol Na
Step 3: 1 mole Na = 6.02 × 1023 atoms Na
= 7.22 × 1022 atoms Na0.120 mol Na ×1 mol Na
6.02 × 1023 atoms Na
How many moles of potassium are in 1.25 × 1021 atoms K?
Step 1: we want moles K
Step 2: we have 1.25 × 1021 atoms K
Step 3: 1 mole K = 6.02 × 1023 atoms K
= 2.08 × 10-3 mol K 1.25 × 1021 atoms K ×1 mol K
6.02 × 1023 atoms K
How many atoms are present in 1 mole of hydrogen atoms?
6.02 x 1023 H atoms
How many atoms are present in 1 mole of 12C atoms?
6.02 x 1023 12C atoms
How many moles are present in 2.67 x 10 23 molecules of N2H4(ammonium)
Moles N2H4 = 2.67 x 1023 Molecules N2H4
1 mol N2H4
6.02x1023 molecules N2H4
= 0.44 mol N2H4
Molar MassOften called as Molecular Weight
Molar mass is the mass of 1 mole of in grams
eggsshoes
marblesatoms
1 mole 12C atoms = 6.02 x 1023 atoms = 12.00 g
1 12C atom = 12.00 amu
1 mole 12C atoms = 12.00 g 12C
1 mole lithium atoms = 6.941 g of Li
For any elementatomic mass (amu) = molar mass (grams/mol)
M= molar mass in g/mol
NA = Avogadro’s number
Eg : Oxygen occurs naturally as a diatomic, O2, the molar mass of oxygen gas is 2 times 16.00 g or 32.00 g/mol.
The molar mass of a substance is the sum of the molar masses of each element.
What is the molar mass of magnesium nitrate, Mg(NO3)2?
The sum of the atomic masses is:
24.31 + 2(14.01 + 16.00 + 16.00 + 16.00) =
24.31 + 2(62.01) = 148.33 amu
The molar mass for Mg(NO3)2 is 148.33 g/mol.
Now we will use the molar mass of a compound to convert between grams of a substance and moles or particles of a substance.
6.02 × 1023 particles = 1 mol = molar mass
If we want to convert particles to mass, we must first convert particles to moles and than we can convert moles to mass.
What is the mass of 1.33 moles of titanium, Ti?
We want grams, we have 1.33 moles of titanium.
Use the molar mass of Ti: 1 mol Ti = 47.87 g of Ti
= 63.67 g Ti1.33 mole Ti ×47.87 g Ti
1 mole Ti
What is the mass of 2.55 × 1023 atoms of lead?
We want grams, we have atoms of lead.
Use Avogadro’s number and the molar mass of Pb
= 87.8 g Pb
2.55 × 1023 atoms Pb ×1 mol Pb
6.02×1023 atoms Pb
207.2 g Pb
1 mole Pb×
How many O2 molecules are present in 0.470 g of oxygen gas?
We want molecules O2, we have grams O2.
Use Avogadro’s number and the molar mass of O2
= 8.84 × 1021 molecules O2
0.470 g O2×1 mol O2
32.00 g O2
6.02×1023 molecules O21 mole O2
×
We can also use molar volume to calculate the molar mass of an unknown gas.
1.96 g of an unknown gas occupies 1.00L at STP. What is the molar mass?
We want g/mol, we have g/L.
1.96 g
1.00 L22.4 L1 mole× = 43.9 g/mol
We now have three interpretations for the mole:
1 mol = 6.02 × 1023 particles
1 mol = molar mass
1 mol = 22.4 L at STP for a gas
This gives us 3 unit factors to use to convert between moles, particles, mass and volume.
A sample of methane, CH4, occupies 4.50 L at STP. How many moles of methane are present?
We want moles, we have volume.
Use molar volume of a gas: 1 mol = 22.4 L
4.50 L CH4× = 0.201 mol CH41 mol CH422.4 L CH4
Chemical Equations
Reactants: Zn + I2 Product: Zn I2
Main Ideas
Chemical Reactions are represented by Chemical Equations.
Chemical Equations are balanced to show the same number of atoms of each element on each side.
The Law of Conservation of Mass says that atoms won’t be created or destroyed in a chemical reaction. That is why you have to balance chemical equations!
Chemical Equations are different from Numerical Equations
Numerical Equation: 3x + 2y = 47
Chemical Equation 2Na + Cl2 2NaCl
Reactant A + Reactant B Product
The reactants are used up in forming the product
The arrow shows the direction of the reaction
Symbols used in Chemical Equations
Symbol Purpose
+ Separates more than one reactant
or product
Separates reactants from products.
Indicates direction of reaction
(s) Identifies a solid state
(aq) Identifies that something is
dissolved in water
(l) Identifies liquid state
(g) Identifies gaseous state
In a chemical reaction, matter is neither created nor destroyed.
Atoms won’t change their identity (e.g. a Carbon atom can’t become an Iron atom).
This means that you have to have the same number of each type of atom on each side of the chemical equation.
Balancing EquationsAfter you write a chemical equation you have to balance it to make sure that
the same number of atoms of each element are on each side.
How would you balance this equation?
Li + H2O H2 + LiOH
Steps to Balancing a Chemical Equation
6. Check your work
5. Write the Coefficients in their lowest possible ratio
4. Change to Coefficients to make the number of atoms of each element equal on both sides of arrow
2 Li(s) + 2 H2O (l) H2(g) + 2 LiOH(aq)
3. Count the atoms of the elements in the products
1 atom Li, 3 atoms H, 1 atom O
2. Count the atoms of the elements in the reactants
1 atom Li, 2 atoms H, 1 atom O
Li (s) + H2O (l) H2 (g) + LiOH (aq)
Another Example
CH4 (methane gas) + O2 CO2 + H2O
7 ≠ 6!Where did our atoms go?
Reactants Products
# of Carbons = 1 # of Carbons = 1
# of Hydrogens = 4 # of Hydrogens = 2
# of Oxygens = 2 # of Oxygens = 3
Total atoms = 7 Total atoms = 6
Example Continued
Change the Coefficients to make the number of atoms of each element equal
Balance the Hydrogens:
CH4 + O2 CO2 + 2 H2O
Balance the Oxygens:
CH4 + 2 O2 CO2 + 2 H2O
Example Continued
CH4 + 2 O2 CO2 + 2 H2OAre your coefficients in their simplest ratio?
Count your atoms again to check your work:
Reactants Products
# of Carbons = 1 # of Carbons = 1
# of Hydrogens = 4 # of Hydrogens = 4
# of Oxygens = 4 # of Oxygens = 4
Total atoms = 9 Total atoms = 9
Balancing Equations
___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)
http://xbeams.chem.yale.edu/~batista/113/movies/04m02vd1.mov
Balancing Equations
____C3H8(g) + _____ O2(g) ---->
_____CO2(g) + _____ H2O(g)
____B4H10(g) + _____ O2(g) ---->
___ B2O3(g) + _____ H2O(g)
http://xbeams.chem.yale.edu/~batista/113/movies/04m04an1.mov
Try These!
C2H6 + O2 CO2 + H2O
Fe2O3 + H2SO4 Fe2(SO4)3 + H2O
Hint : balance the polyatomic ion first!
CaCl2 + AgNO3 AgCl + Ca(NO3)2
Think – Pair - Share
Types of Reaction
Chemical Reactions
Chemical Reaction:
a process in which the physical andchemical properties of the original substance change as new substances with different physical and chemical properties are formed
Chemical Reaction Basics
H2 + O2 --> H2O
Reactants- substance that enters into a reaction
Products- substance that is produced by a chemical reaction
Reactants Products
Evidence of Chemical Change
EPOCH is an acronym that stands for evidence that a chemical reaction has occurred.
– Effervescence (bubbles and/or gives off gas)
– Precipitate (solid crystals form)
– Odor (change of smell is detected)
– Color change
– Heat (reaction either heats up or cools down)
Does sighting evidence of a chemical reaction mean that a chemical reaction has undoubtedly taken place?
E
P
O
C
H
Chemical Reactions are Everywhere
Cooking Respiration
Chemical Reactions are Everywhere
Hair Dye Auto Fuel
How do you know when a chemical reaction takes place?
Color Change Precipitate Formation
How do you know when a
chemical reaction takes place?Gas Formation
Odor
How do you know when a chemical reaction takes place?
Temperature Change Change in Acidity
Representing Chemical Reactions
Chemists observe chemical reactions and have come up with a way to represent or model what is happening.
Making NaCl
Solid Sodium combines with Chlorine gas to make solid Sodium Chloride:
2Na (s) + Cl2 (g) 2NaCl
http://www.angelo.edu/faculty/kboudrea/demos/sodium_chlorine/sodium_chlorine.htm
1. Synthesis - Marriage/Dating
A + B = AB
Example C + O2
OOC + O OC
Cartoon Chemistry
This is an example of synthesis
Ex: Synthesis Reaction
Practice : Synthesis Reaction
Predict the products.
Na(s) + Cl2(g)
Mg(s) + F2(g)
Al(s) + F2(g)
NaCl(s)
MgF2(s)
AlF3(s)
22
2 3 2
• Now, balance them.
2. Decomposition
AB= A + B
Example: NaCl
Cl Na Cl + Na
Cartoon Chemistry
This is an example of a decomposition
Ex: Decomposition Reaction
3. Single-Replacement
A + BC = AC + B
Example: Zn + CuCl2
ZnClClCu +
ClClZn
Cu+
Zn was oxidized
Went from neutral (0) to (+2)
Cu was reduced
Went from (+2) to Neutral (0)
Cartoon Chemistry
This is an example of a single replacement
Ex: Single Replacement Reaction
Single Replacement Reactions
Write and balance the following single replacement reaction equation:
• Zn(s) + HCl(aq) ZnCl2 + H2(g)2
• NaCl(s) + F2(g) NaF(s) + Cl2(g)
• Al(s)+ Cu(NO3)2(aq)
2 2
Cu(s)+ Al(NO3)3(aq)3 23 2
4. Double-Replacement
AB + CD = AC + BD
Example: MgO + CaS
SO
Mg Ca+OS
Mg Ca+
Cartoon Chemistry
This is an example of a double replacement
Double Replacement Reactions
Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together
Example:
AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)
Another example:
K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2
5. Combustion Reaction
Combustion reactions - a hydrocarbon reacts with oxygen gas.
This is also called burning!!!
In order to burn something you need the 3 things in the “fire triangle”:
1) Fuel (hydrocarbon)2) Oxygen 3) Something to ignite the reaction (spark)
Combustion Reactions
In general: CxHy + O2 CO2 + H2O
Products are ALWAYS
carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)
Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)
Combustion
Example
• C5H12 + O2 CO2 + H2O
Write the products and balance the following combustion reaction:
• C10H22 + O2
5 68
Reaction Types Review…
Match each chemical reaction with one of the reaction types on your chemical cartoons.
– Zn + 2HCl H2 + ZnCl2
– N2 + 3H2 2NH3
– 2KI + Pb(NO3)2 2KNO3 + PbI2
– 2MgCl Mg2 + Cl2
Mixed Practice
State the type & predict the products.
1. BaCl2 + H2SO4
2. C6H12 + O2
3. Zn + CuSO4
4. Cs + Br2
5. FeCO3
Oxidation-
Reduction
reaction
Oxidation-Reduction Reactions
Electron transfer reactions
Electrons transferred from one substance to another
Originally only combustion of fuels or reactions of metal with oxygen
Important class of chemical reactions that occur in all areas of chemistry & biology
Also called redox reactions
Oxidation–Reduction Reactions
Involves 2 processes:
Oxidation = Loss of Electrons (OIL)Na Na+ + e Oxidation Half-Reaction
Reduction = Gain of electrons (RIG)Cl2 + 2e
2Cl Reduction Half-Reaction
Net reaction:
2Na + Cl2 2Na+ + 2Cl
– Oxidation & reduction always occur together
– Can't have one without the other
Reducing Agent
Substance that donates e's
Releases e's to another substance
Substance that is oxidized
Na Na+ + e–
Oxidizing Agent
Substance that accepts e's
Accepts e's from another substance
Substance that is reduced
Cl2 + 2e 2Cl–
Oxidation–Reduction Reactions
Redox Reactions
Very common
Batteries—car, flashlight, cell phone, computer
Metabolism of food
Combustion
Chlorine Bleach
Dilute NaOCl solution
Cleans through redox reaction
Oxidizing agent
Destroys stains by oxidizing them
Redox ReactionsEx. Fireworks displays
Net: 2Mg + O2 2MgO
Oxidation:
Mg Mg2+ + 2e
Loses electrons = Oxidized
Reducing agent
Reduction:
O2 + 4e 2O2
Gains electrons = Reduced
Oxidizing agent
Your Turn!
Which species functions as the oxidizing agent in the following oxidation-reduction reaction?
Zn(s) + Pt2+(aq) Pt(s) + Zn2+(aq)
A. Pt(s)
B. Zn2+(aq)
C. Pt2+(aq)
D. Zn(s)
E. None of these, as this is not a redox reaction.
Net: Zn(s) + Pt2+(aq) Pt(s) + Zn2+(aq)
Oxidation: Zn Zn2+ + 2e
Loses electrons = Oxidized
Reducing agent
Reduction: Pt2+ + 2e Pt
Gains electrons = Reduced
Oxidizing agent
So, oxidizing agent = Pt2+
Example 1
Zn(s) Zn2+(aq) + 2e oxidation
Cu2+(aq) + 2e Cu(s) reduction
Each half-reaction is balanced for atoms
Same # atoms of each type on each side
Each half-reaction is balanced for charge
Same sum of charges on each side
Add both equations algebraically, canceling e’s
NEVER have e's in net ionic equation
Cu2+(aq) + Zn(s) Cu(s) + Zn2+(aq)
Left = Zn(s) + CuSO4(aq)
Center = Cu2+(aq) reduced to Cu(s); Zn(s) oxidized to Zn2+(aq)
Right = Cu(s) plated out on Zn bar
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)
Zn2+ ions take place of Cu2+ ions in solution
Cu atoms take place of Zn atoms in solid
Cu2+ oxidizes Zn° to Zn2+
Zn° reduces Cu2+ to Cu°
More active Zn°replaces less active Cu2+
Zn°is easier to oxidize!
Activity Series of Metals
Cu less active, can't replace Zn2+
Can't reduce Zn2+
Cu(s) + Zn2+(aq) No reaction
General phenomenon
Element that is more easily oxidized will displace one that is less easily oxidized from its compounds
Activity Series (Table 6.3)
Metals at bottom more easily oxidized (more active) than those at top
This means that given element will be displaced from its compounds by any metal below it in table
Learning Check: Metal Activity
Using the following observations, rank these metals from most reactive to least reactive:
Cu(s) + HCl(aq) → no reaction
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
Mg(s) + ZnCl2(aq) → MgCl2(aq) + Zn(s)
Mg > Zn > H > Cu
Table Activity Series of Some Metals
STOICHIOMETRY
Stoichiometry is the calculation of relative quantities of reactants and products in chemical reactions.
http://www.snipview.com/search?q=Reactanthttp://www.snipview.com/search?q=Product_(chemistry)http://www.snipview.com/search?q=Chemical_reaction
Stoichiometry
Like any other stoichiometry problem
• Balance reaction
• Use stoichiometric coefficients to relate mole of 1 substance to moles of another
Types of problems
• Start with mass or volume of one reactant & find mass or volume of product
• Perform titrations
• Have limiting reactant calculations
• Calculate % yields
Example of Stoichiometry Equation
What Mass of NaCl can be produced by reacting 12.0 grams of sodium, Na, with
an excess of chlorine gas, Cl2?
The Balanced equation: 2Na + Cl2 → 2NaCl
= 12.0 g Na X 1 mole Na X 2 mole NaCl X 58.5 g NaCl
23.0 g Na 2 mole Na 1 mole NaCl
= 30.5 g NaCl
Exercise of Stoichiometry
If 120.00 g of propane, C3H8, is burned in excess oxygen, how many grams of water are formed?
CHAPTER 1 - 4