Unit1 Chapter3 notes B and L.ppt

Unit 1

Chemical Equations

Anatomy of a Chemical Equation

Anatomy of a Chemical Equation

CH

(

g

) + 2O

(

g

)

CO

(

g

) + 2H

O(

g

)

Anatomy of a Chemical Equation

CH

(

g

) + 2O

(

g

)

CO

(

g

) + 2H

O(

g

)

Anatomy of a Chemical Equation

CH

(

g

) + 2O

(

g

)

CO

(

g

) + 2H

O(

g

)

Anatomy of a Chemical Equation

CH

(

g

) + 2O

(

g

)

CO

(

g

) + 2H

O(

g

)

© 2012 Pearson Education, Inc.

Subscripts and Coefficients Give

Different Information

• Subscripts tell the number of atoms of each element in a molecule.

Balancing Equations

*Equations must be balanced b/c of the Law of Conservation of Mass

Examples:

__Fe(s) + __O₂(g)  _{___Fe2O3(s)}

*use a coefficient to make same # of atoms on both sides of the arrow. _4_Fe(s) + _3_O₂(g)  _{_2_Fe2O3(s)}

States of matter and other notations:

(s) = solid (aq) = aqueous (not a pure liquid) (l) = liquid (g) = gas

*substances to be (l): H₂O(l), Hg(l), Br₂(l), also might see nonpolar pure substances: butane, C

¾ 

¾

heat is needed

substance

¾

¾¾¾



“Tricks of the Trade”

Balancing polys:

*keep poly whole, don’t break up into

individual atoms

__Al + __H

SO



__H

+ __Al

(SO

)

Balancing odd # of atoms:

Don’t forget HONCl BrIF!

When ever hydrogen, nitrogen, oxygen,

fluorine, chlorine, bromine, iodine are

reactants or products they are always

represented as diatomics:

H

, N

, O

, F

, Cl

, Br

, I

You Try:

1. __C

H

+ __O



__CO

+ __H

O

2. __Pb(OH)

+__ HCl



__H

O + __PbCl

3. __S

+ __O



__SO

Models To Represent Rxns

Write a balanced chemical equation to describe the model above.

Calculating Formula Weights or

Molecular Weights

(We called this molar mass in 10th grade.)

Steps:1. List all elements in molec/compd 2. List the number of ea. Element

3. Look up each atomic mass of element.

4. Multiply number of each type of element by its atomic mass.

Example:

Calculate the formula weight of Calcium

nitrate.

Formula: Ca(NO₃)₂

Ca: 1 x 40.1 amu = 40.1 amu N: 2 x 14.0 amu = 28.0 amu O: 6 x 16.0 amw = 96.0 amu

164.1 amu

You Try…

Calculate the molecular/formula weight of:

1.Sucrose, C₁₂H₂₂O₁₁ 2.Ammonium phosphate 3.Calcium chloride

4.Aluminum oxide 5.Iron (II) nitride

Hydrates

Some metal compounds obtained from aqueous solution contain water molecules as part of their hydrated complex.

Example: CuSO₄ * 5H₂O There are 5 mols of water associated with this

Formula Weight Calculations

with Hydrates

Almost same process as anhydrous compounds. Calculate formula

weight of CuSO₄ * 5H₂O.

*Note: the *5 does not literally mean multiply, it means associated.

1. Find the Formula

weight of each part. 2. Multiply water’s

molecular weight by # of associated water molecules.

Calculation:

CuSO

* 5H

O

CuSO

:

Cu: 1 x 63.55 = 63.55 amu

S: 1 x 32.06 = 32.06 amu

O: 4 x 16.00 = 64.00 amu

159.61amu

H₂O:

H: 2 x 1.008 = 2.016 amu O: 1 x 16.00 = 16.00 amu 18.02 amu 5 (18.02 amu) = 90.10amu

You Try…

A hydrate of magnesium sulfate, commonly known as Epsom salt has the formula: MgSO₄ 7 H₂O.

Calculate the formula weight of this hydrate.

Percent Composition

• The percent by mass of each element in

a molecule or compound.

• Percentages must add to 100%

• Formula:

(no. of atoms)(atomic weight)

Example:

1. Determine molar masses of each element:

C: 1 x 12 = 12 amu

H: 4 x 1= 4 amu

2. Determine the total molar mass:

CH₄ = 12+4 = 16 amw

3. Divide element mass by total mass:

C: 12 x 100= 75% C 16

H: 4 x 100= 25% H 16

Empirical and Molecular

Formulas

• An empirical formula shows the lowest whole

number mole ratio of the elements in a compd/molec. • A molecular formula is the actual formula of the

compd/molec.

– _{molecular formula = (empirical formula)molecular formula = (empirical formula)nn}

[[nn = integer] = integer]

• Compare the empirical and molecular formulas of caffeine:

C₄H₅N₂O vs C₈H₁₀N₄O₂

What about Ionic Compounds?

What about Ionic Compounds?

Formulas for

Formulas for ionic compounds ionic compounds are are ALWAYSALWAYS

empirical

empirical (lowest whole number ratio). _{(lowest whole number ratio).}

Examples:

Examples:

What about molecular formulas?

What about molecular formulas?

Formulas for

Formulas for molecular compounds molecular compounds MIGHT_MIGHT

be empirical (lowest whole number ratio).

be empirical (lowest whole number ratio).

Molecular: Molecular:

H₂O

C₆H₁₂O₆ C₁₂H₂₂O₁₁

Empirical:

H₂O

CH₂O C₁₂H₂₂O₁₁

Steps for Determining Empirical

Formulas:

1. Take %’s and turn into grams to assume there is a 100g total sample. 2. Divide by molar mass of each element to find mole ratios.

3. Divide all mole ratios by lowest mole ratio number.

4. If not whole number ratios, multiply by 2, 3, 4, etc to get whole number ratio.

Example:

1. C = 60.00 g H = 4.44 g O = 35.56 g

2. C = 60.00 g = 4.995 mol 12.01

H = 4.44 g = 4.41 mol 1.008

O = 35.56 g = 2.223 mol 16.00

3. C = 4.995 = 2.247 x 4 2.223

H = 4.41 = 1.98 x 4 2.223

O = 2.223 = 1.000 x 4 2.223

4. X 4 mole ratios to make whole numbers.

Answer:

Aspirin has a chemical composition of 60.00% C, 4.44% H, and 35.56% O. What is the empirical formula of aspirin?

Aspirin

• Empirical Formula of Aspirin:

• Molecular Formula of Aspirin:

• They are the same

C

H

O

What if they aren’t the same?

Determining Molecular Formulas

1. Determine the molar mass of the EF:

C: 1 x 12.01amu = 12.01amu H: 2 x 1.008 amu= 2.016amu O: 1 x 16.00amw= 16.00amu

30.02amu

2. Divide the MF molar mass by the EF molar mass to determine the whole # ratio

180 = 6 30.02

3.Multiply the subscripts in the EF by the whole #

6 (CH₂O) = C₆H₁₂O₆

Answer:

EF: CH₂O MF: C₆H₁₂O₆

Sample AP Question

When hafnium metal is heated in an atmosphere of chlorine gas, the product of the reaction is found to contain 62.2 percent Hf by mass and 37.4 percent Cl by mass. What is the empirical formula for this compound?

Sample AP Question

A compound contains 1.10 mol of K, 0.55 mol of Te, and 1.65 mol of O. What is the simplest formula of this compound?

Sample AP Question

A sample of a compound contains 3.21 g of sulfur and 11.4 g of fluorine. Which of the following represents the empirical formula of the compound?

What about empirical formulas of

hydrates?

A 0.386 g sample of sodium sulfate hydrate with the general formula Na₂SO₄ xH₂O is heated. The mass after heating is 0.170 g. What is the formula and

Hydrates: You Try…

A hydrate of copper(II) chloride has the formula: CuCl₂ xH₂O. A 3.41 g sample of the hydrate is

heated. The remaining sample has a mass of 2.69 g. Find the empirical formula of the compound.

The Mole!

Avogadro’s Number:

the amount of

atoms/substances/objects per mole.

6.022 x 1023 mol-1

*Memorize this N_A as a variable

Since atoms, molecules, or ions are extremely small, the number of individual particles in a substance is extremely LARGE!

Converting Substances

Calculations with Moles:

Calculations with Moles:

Converting moles to grams

Converting moles to grams

How many grams of lithium are in 3.50 moles of lithium?

3.50 mol Li

= g Li 1 mol Li

6.94 g Li

Calculations with Moles:

Calculations with Moles:

Converting grams to moles

Converting grams to moles

How many moles of lithium are in 18.2 grams of lithium?

18.2 g Li

= mol Li 6.94 g Li

1 mol Li

Calculations with Moles:

Calculations with Moles:

Using Avogadro

Using Avogadro

’

’

s Number

s Number

How many atoms of lithium are in 3.50 moles of lithium?

3.50 mol Li

= atoms Li 1 mol Li

6.02 x 1023 atoms Li

Calculations with Moles:

Calculations with Moles:

Using Avogadro

Using Avogadro

’

’

s Number

s Number

How many atoms of lithium are in 18.2 g of lithium?

18.2 g Li

= atoms Li 1 mol Li 6.02 x 1023 atoms Li

1.58 x 1024

6.94 g Li 1 mol Li

Calculations with Moles:

Calculations with Moles:

Using Avogadro

Using Avogadro

’

’

s Number

s Number

0.350 mol C6H12O6

= atoms H 6.02 x 1023 molec C

6H12O6

2.58 x 1024

1 mol C₆H₁₂O_{6 1 molec C}

6H12O6

(0.350)(6.022 x 1023)(12)

Simple Types of Reactions

Combination (Synthesis):

2 or more reactants form 1 product.

Nitrogen gas and hydrogen gas produce ammonia gas.

N₂(g) + 3H₂(g)  2NH₃(g)

Decomposition: 1 reactant produces 2 or more products.

Solid potassium chlorate

decomposes to produce solid potassium chloride and oxygen gas.

Stoichiometry

Stoichiometry

Using the balanced coefficients as mole

Using the balanced coefficients as mole

ratios in problems.

ratios in problems.

C

C22HH55OH + 3OOH + 3O22  2CO 2CO22 + 3H + 3H22OO

1

1 mole of ethanol mole of ethanol reacts with 3reacts with 3 moles of oxygen moles of oxygen

to produce

to produce 22 moles of carbon dioxide moles of carbon dioxide and 3and 3 moles moles of water

of water

When the equation is balanced it has quantitative

When the equation is balanced it has quantitative

significance:

Working a Stoichiometry Problem

Working a Stoichiometry Problem

6 moles of aluminum reacts with an excess of oxygen. How many moles of aluminum oxide are formed.

1. Identify reactants and products and write the balanced equation.

Al + O_{2 Al2O3}

a. What are the reactants?

b. What are the products?

c. What are the balanced coefficients?

Working a Stoichiometry

Working a Stoichiometry

Problem

Problem

6.50 grams of aluminum reacts with

an excess of oxygen. How many

grams of aluminum oxide are formed?

Working a Stoichiometry Problem

Working a Stoichiometry Problem

6 moles of aluminum reacts with an excess of oxygen. How many moles of aluminum oxide are formed?

4 Al + 3 O₂  2Al₂O₃

=

6 mol Al

? mol Al₂O₃ 2 mol Al₂O₃

4 mol Al

Working a Stoichiometry Problem

Working a Stoichiometry Problem

6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed?

4 Al + 3 O₂  2Al₂O₃

=

6.50 g Al

? g Al₂O₃ 1 mol Al

27.0 g Al 4 mol Al 2 mol Al₂O₃

1 mol Al₂O₃ 102. g Al₂O₃

You Try

You Try

Solid lithium hydroxide reacts with

carbon dioxide gas to produce solid

lithium carbonate and liquid water.

How many grams of carbon dioxide

can be absorbed by 1.00 grams of

lithium hydroxide?

You Try

You Try

Solid lithium hydroxide reacts with carbon

dioxide gas to produce solid lithium carbonate and liquid water. How many grams of carbon dioxide can be absorbed by 1.00 grams of lithium hydroxide?

2LiOH(s) + CO₂(g)  Li₂CO₃(s) + H₂O(l)

=

1.00 g LiOH

? g Al₂O₃ 1 mol LiOH

24.0 g LiOH2 mol Al 1 mol CO₂

1 mol CO₂ 44.0 g CO₂

What are Limiting Reactants?

2 1/4 cups all-purpose flour 1 teaspoon baking soda

1 teaspoon salt

1 cup (2 sticks) butter 3/4 cup granulated sugar 3/4 cup packed brown sugar 1 teaspoon vanilla extract 2 large eggs

1 bag chocolate chips

Terminology:

1. Limiting Reactant (LR): the reactant that

will be used up first during a chemical

reaction.

2. Excess Reactant: the reactant that will be

left over when the reaction is complete

Percent Yield:

% yield

=

Actual amount

theoretical amount

x 100

Actual: the amount of product actually

produced

Example

212 grams of solid sodium carbonate reacts with

134 grams of solid copper(II) chloride to produce

aqueous sodium chloride and solid copper(II)

carbonate. Which is the limiting reactant?

Steps:

2. Set up a Mass to Mass Stoich problem and compare the two reactants to each other.

212 g Na₂CO₃

= 268.9 g CuCl₂ 1 mol Na₂CO₃

106.0 g Na₂CO₃ 1 mol Na₂CO₃ 1 mol CuCl₂

1 mol CuCl₂ 134.5 g CuCl₂

3. Compare the amount of reactant needed to the amount given to you.

Given: 134 g CuCl₂ Needed: 268.9 g CuCl₂

More Questions

1. How many grams of the excess reactant

are left over?

2. How many grams of copper (II) carbonate

are theoretically produced?

3. If this reaction is performed and 62 grams

of copper (II) carbonate is actually

“Integrated” Problem

Isopropyl alcohol, sold as rubbing alcohol, is

composed of C, H and O. Combustion of

Step 1:

1. Find how many grams of C and H there are by

Step 2:

2. Find how many grams of oxygen there

should be if the Law of Conservation of

Mass is obeyed.

Step 3:

3. Determine the number of moles of each

substance by converting grams of each

Step 4:

4. Create small, whole number mole ratios by

dividing by smallest number of moles.

Multiply by a small number to fix ratios if

needed.

AP Sample Question

A sample of a compound that contains only the elements C, H, and N is completely burned in O₂ to produce 44.0 g of CO₂, 45.0 g of H₂O, and some NO₂ . A possible empirical formula of the compound is