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