Stoichiometry Chapter 11 & 12. I. Things you should remember From the Moles Unit: Identify particles as atoms, molecules (mc), and formula units (fun)

Stoichiometry Chapter 11 & 12

I. Things you should remember

• From the Moles Unit:• Identify particles as atoms, molecules (mc),

and formula units (fun)• 1 mole = 6.02 x 1023 atoms, molecules, or

formula units• 1 mole atom = mass (in grams) from the

periodic table• From the Naming & Formulas Unit:

• How to write a formula given a chemical name

• From the Chemical Reactions Unit:• How to write a chemical equation given words• Balancing equations

Example 1: Determine the moles of magnesium there are in 1.23 x 1024 atoms of magnesium

1.23 x 1024 atoms Mg

1 mole Mg

6.02 x 1023 atoms Mg

= 2.04mol Mg

1

G: 1.23 x 1024 atoms MgW: moles MgR: 1 mole Mg = 6.02 x 1023 atoms Mg

Example 2: Determine the mass of 3.50 mol of copper.

3.50 mol Cu 63.546g Cu

1 mol Cu

= 222g Cu

From the p.t Copper: 63.546g Cu = 1 mol Cu

1

Example 3: Calcium and sodium carbonate react together to form calcium carbonate and sodium

Na+ CO32-

Ca +

CaCO3Na2CO3

Ca2+ CO32-

Na+

Example 4: Balance Li2O(s) + H2O(l) LiOH(aq)

Li2O(s) + H2O(l) LiOH(aq) 2

Practice1. Determine the number of water molecules in 11.2 moles of water.

11.2 moles H2O 6.02 x 1023 molecules H2O

= 6.74 x 1024

1 moles H2O

molecules H2O

1

G: 11.2 moles waterW: mc waterR: 1 mole H2O = 6.02 x 1023 mc H2O

Practice 2. Determine the number of moles in 11.9 kg of aluminum.

11.9 kg Al 1000g Al

1 kg Al= 4411 mol Al

26.982g Al

From the p.t Aluminum: 26.982g Al = 1 mol Al

mol Al1

G: 11.9 kg AlW: mol AlR: 1 mole Al = 26.982g Al 1 kg Al = 1000g Al

Quick Review:Writing Formulas for

Ionic Compounds

A reminder of what a chemical formula tells us:

EX: aluminum carbonate

Al3+ CO32-

Al2(CO3)3

CO32-

Al3+

Al3+

Al2(CO3)3CO3

2-

CO32-

in 1 formula unit of aluminum carbonate:

2 moles aluminum

3 moles carbons9 moles oxygens

2 atoms aluminum

3 atoms carbons9 atoms oxygens

Al2(CO3)3

Al

o

C

o

o

Al

o

C

o

o

o

C

o

o2 moles Al3 moles CO3

II. Quantifying Chemical

Compounds

II. Quantifying Chemical Compounds

We will now do the same thing, but we will have questions that are more detailed about the compounds. First we need to know how to find the molar mass of the whole compound.

I. Molar Mass

1. Definition

• Remember, molar mass is the mass (in grams) of one mole of an element or compound.

2. Determining Molar Mass

• The molar mass of the compound is the sum of the molar masses of each atom in the compound.

• The units for molar mass are grams per mole (g/mol).

Gramsmole

Ex: Determine the molar mass of sulfur trioxide.

80.063 g/mol or 80.063 g = 1 mole SO3

SO3

+ =X 3(47.997 g)

For the sake of consistency…

When calculating molar masses, use all the sig figs presented on your periodic

table

Let’s show all of our molar masses to the thousands place (you should know it’s not going to make a huge difference)

Ex: 18.015g/mol

But, show our final final stoichiometry answers in 3 sig figs

Ex: Determine the molar mass of calcium nitrate.

Ca(NO3)2

+ 2164.088 g/mol or 164.088 g = 1 mol Ca(NO3)2

=

Ex: Determine the molar mass of calcium nitrate.

Ca(NO3)2

+ =X 2 + X 6

164.088 g/mol or 164.088 g = 1 mol Ca(NO3)2

Ex: Determine the molar mass of Iron(III) sulfate.

Fe3

+

(SO4)2-

(SO4)2-Fe3

+ (SO4)2-

Fe2(SO4)3

First you need the right formula right?

Ex: Determine the molar mass of Iron(III) sulfate.

Fe2(SO4)3

+X 2 + X 12

399.88 g/mol or 399.88 g = 1 mol Fe2(SO4)3

X 3

Practice:1. Determine the molar mass of

each of the following.a. Li2S

b. (NH4)2CO3

C. magnesium hydroxide

d. copper (II) iodide

45.948 g/mol Li2S 96.086 g/mol

(NH4)2CO3

58.319 g/mol Mg(OH)2

317.354 g/mol CuI2

3. Using Molar Mass in Calculations

You would use the molar mass of a compound in dimensional analysis just

like you did with elements.

Ex: Determine the mass of 48.6 moles of sodium chloride.

Step 1: Write the formula for sodium chloride.

Na+ Cl-

NaCl


Step 2: set up a dimensional analysis problem

G:

W:

R:

48.6 moles NaCl

Mass (g) NaCl


Step 3: Find the molar mass for NaCl because the wanted is MASS

Na = 1 X g = 22.990g

Cl = 1 X g = 35.453g

58.443g/mol NaCl


Step 3: Plug it all in

48.6 mol NaCl 58.443g NaCl1 mol NaCl

= 2.84 x 103g NaCl= 2840g NaCl

Tips for working molar mass problems1. If mass is involved in your problem, determine molar mass of compound.

1 mole X = ____________ g X

2. If you see the terms: atoms, molecules, or formula units, use Avogadro’s number.

1 mol X = 6.02 X 1023___*___ X* atoms, molecules or formula units

Ex: Determine the number of moles in 582 g of magnesium

nitrate Step 1: Write the formula for magnesium

nitrate

Mg+2 NO3-

Mg(NO3)2

Ex: Determine the number of moles in 582 g of potassium

nitrateStep 2: set up a dimensional analysis

problem

G:

W:

R:

582 g Mg(NO3)2

Moles Mg(NO3)2


nitrate.Step 2: Find the molar mass for

Mg(NO3)2

Mg = 1 X 24.305 g = 24.305 gN = 2 X 14.007 g = 28.014 gO = 6 X 15.999 g = 95.994 g

148.313 g/mol Mg(NO3)2


nitrate.Step 3: Set up a dimensional analysis

problem.

582g Mg(NO3)2 148.313g Mg(NO3)2

1 mol Mg(NO3)2

= 3.92 mol Mg(NO3)2

Reminder:

How to type in Scientific Notation into a scientific calculator

6.02 x 1023

Keystrokes:6.02 EE or EXP

23 (2nd X-1)

Ex: Determine the number of molecules in 47.3 g of sulfuric acid.

47.3g H2SO4 1 mol H2SO4

98.078g H2SO4

6.02 x 1023 molecules H2SO4

1 mol H2SO4

= 2.90 x 1023 molecules H2SO4

1

G:

W:

R:

47.3 g H2SO4

Molecules of H2SO4

1 mol H2SO4 = g H2SO4

1 mol H2SO4 = 6.02 x 1023 mc H2SO4

98.078

Practice

1. Determine the number of moles in 27.4 g of TiO2.

2. Determine the mass of 9.45 mol of dinitrogen trioxide.

3. Determine the mass (in kg) of 5.83 x 1023 molecules of HCl.

3. Determine the number of molecules in 782g of N2O3.

0.343 mol TiO2

0.0353 kg HCl

6.19 x 1024 molecules N2O3

567g N2O3

II. Percent Composition


• The relative amounts of each element in a compound are expressed as percentages.

• The percent by mass of an element in a compound is the total number of grams of the element divided by the molar mass of the compound multiplied by 100%.


Identify all of the atoms in the compound and solve using the equation below to find the abundance of each element.

% composition =

Mass elementMolar Mass

X 100

(Mass of Compound)

Ex: Calculate the % composition of propane (C3H8). (In other words, what

percent of propane is carbon and what percent is hydrogen?)

Carbon 3 x = 36.033g/mol

Hydrogen 8 x = 8.064g/mol

Molar mass = 44.097 g/mol

Ex: Calculate the % composition of propane (C3H8)

% compositionC =

36.033g/mol

44.097 g/mol100

% compositionH =

8.064g/mol

44.097 g/mol100

81.7% C

18.3% H

Ex: Calculate the % composition of propane (C3H8)

These calculations tell us that 81.7% of propane is composed of carbon and

18.3% is made up of hydrogen

Note: Percentage is part over whole.Mass of one type of element in a

compound / mass of the whole compound

Ex: Determine the percent nitrogen in zinc nitrate.

Zn2+ NO3-

Zn(NO3)2

%N = 28.014 g/mol

100 189.398 g/mol

To Calculate Molar Mass:

Zn = 1 x 65.39 g/mol = 65.39 g/mo

N = 2 x 14.007 g/mol = 28.014 g/mol

O = 6 X 15.999 g/mol = 95.994 g/mol

Molar mass: 189.398 g/mol

14.8% of N in zinc nitrate =

EX: Determine the mass of sodium in 450 g of sodium

chloride.Na = 22.990 g/molCl = 35.453 g/mol 58.443 g/mol

%Na = 22.990 g/mol

100 58.443 g/mol

39.3% of Na in sodium chloride =

0.393 x 450g = 176g Na

Practice1. Calculate the percent composition of

a. calcium chloride

b. potassium nitrate

2. Determine the percent oxygen in calcium carbonate

3. Calculate the mass of hydrogen ina. 350 g of C2H6

b. 2.14 g NH4Cl

36.1 %Ca, 63.9 % Cl

38.7 % K, 13.9 % N, 47.5 %O

48.0 % O

70.4 g H

0.161 g H

Documents

Stoichiometry Chapter 11 & 12. I. Things you should remember From the Moles Unit: Identify particles as atoms, molecules (mc), and formula units (fun)