1. Chemical Stoichiometry
Chapter 3
Chemical Stoichiometry

2. 3.1: Atomic Mass/Weight The average mass of a sulfur atom is 32.06 amu
The average mass of a sodium atom is amu Na

3. 3.2: Molecular Mass/Weight Formula Mass/Weight
The formula of an Acetylsalicylic Acid (Aspirin) molecule is C9H8O4
Acetylsalicylic Acid (Aspirin) has molecular mass of amu

4. 3.2: Molecular Mass/Weight Formula Mass/Weight
Aluminum sulfate is an ionic compound with the formula Al2(SO4)3
Aluminum sulfate has a formula mass of amu.

5. 3.3: Isotopes
Isotopes are atoms of an element that differ only in the number of neutrons in the nucleus of the atom.
Chlorine has two isotopes:
chlorine – Cl
chlorine – Cl

6. 3.3: Isotopes
In any random sample of chlorine about 1 in 4 atoms is chlorine – 37.
The atomic mass of chlorine is therefore about 35.5 amu.

7. 3.3: Isotopes
How do atoms of chlorine – 35 and chlorine – 37 differ?

8. 3.4: Moles of Atoms and Avogadro’s Number
What is a mole of atoms?

9. 3.4: Moles of Atoms and Avogadro’s Number
What is a mole of atoms?
One mole of magnesium atoms contains
6.02 x 1023 Mg atoms.

10. 3.4: Moles of Atoms and Avogadro’s Number
What is the mass of one mole of Mg atoms?
The atomic mass of Mg is amu.
The molar mass of Mg is grams.

11. 3.5: Moles of Molecules
What is a mole of molecules?

12. 3.5: Moles of Molecules What is a mole of molecules?
One mole of CHCl3 (chloroform) contains 6.02 x 1023 molecules of CHCl3.

13. 3.5: Moles of Molecules What is a mole of molecules?
One mole of CHCl3 (chloroform) contains 6.02 x 1023 molecules of CHCl3.
What else does it contain?

14. 3.5: Moles of Molecules
How many H atoms are in one mole of CHCl3?

15. 3.5: Moles of Molecules How many H atoms are in one mole of CHCl3?
6.02 x 1023 H atoms

16. 3.5: Moles of Molecules
How many Cl atoms are in one mole of CHCl3?

17. 3.5: Moles of Molecules How many Cl atoms are in one mole of CHCl3?
3(6.02 x 1023) Cl atoms

18. 3.5: Moles of Molecules
What is the molar mass of CHCl3?

19. 3.5: Moles of Molecules
What is the molar mass of CHCl3? g

20. Key Concept
You have one mole of ascorbic acid (Vitamin C) C6H8O6. What else do you have?
6.02 x 1023 molecules of C6H8O6
grams of C6H8O6
6 moles C or 6(6.02 x 1023) C atoms
8 moles H or 8(6.02 x 1023) H atoms
6 moles O or 6(6.02 x 1023) O atoms

21. Key Concept
If you have a certain number of moles of any compound you can always find the moles of each element present?
How many mol C are in 0.80 mol of CO2?
How many mol O are in 0.80 mol of CO2?
How many mol H are in 1.2 mol of C12H22O11?
How many mol S are in 3.8 mol of Cr(SO4)3?
How many mol O are in 3.8 mol of Cr(SO4)3?

22. 3.6: Percentage Composition or Percent by Mass
What is the percent by mass of hydrogen in water?

23. 3.6: Percentage Composition or Percent by Mass
A glass of water contains 126g of water. How many grams of hydrogen are present?

24. 3.7: Derivation of Formulas
To calculate a formula of a substance we often use a mole ratio.

25. 3.7: Derivation of Formulas
To calculate a formula of a substance we often use a mole ratio.
Analysis of a gas shows that it is composed of mol carbon and 0.36 mol hydrogen. What is the empirical formula gas?

26. 3.7: Derivation of Formulas
What is the empirical formula of a compound that is 27.29% carbon and 72.71% oxygen.

27. 3.7: Derivation of Formulas
A sample of hematite contains 34.97g of iron and 15.03g of oxygen. What is the empirical formula of hematite?

28. Determine the empirical and molecular formulas for a compound with the following elemental composition: % C, 6.72% H, 53.29% O. The molar mass of the compound is 180. g/mol.

29. Determine the empirical and molecular formulas for a compound with the following elemental composition: % C, 6.72% H, 53.29% O. The molar mass of the compound is 180. g/mol.

30. Determine the empirical and molecular formulas for a compound with the following elemental composition: % C, 6.72% H, 53.29% O. The molar mass of the compound is 180. g/mol.
CH2O

31. Determine the empirical and molecular formulas for a compound with the following elemental composition: % C, 6.72% H, 53.29% O. The molar mass of the compound is 180. g/mol.
CH2O
(1.008) + 1 (16.00) = 30.03
180./30.03 ≈ 6
6(CH2O) = C6H12O6

32. 3.7: Derivation of Formulas
3.22g of a compound decomposes when heated into 1.96g of KCl and oxygen. What is the empirical formula of the compound?

33. 3.8: Solutions
Solute: The substance that dissolves (the minor component of a solution).
KMnO4

34. 3.8: Solutions
Solvent: The substance in which the solute dissolves (the major component of a solution).

35. Solution: A homogeneous mixture of the solute and solvent.
KMnO4 solution

36. 3.8: Solutions
Dilute Concentrated

37. Concentration of a solution
Molarity(M) is the moles of solute per liter of solution.
moles of solute
Molarity(M) =
Liters of solution

38. The next slide lasts between 5 and 6 minutes and can be skipped if needed.

40. Preparation of Solutions
28.3 grams of nickel(II) chloride
Add water to make the desired volume (500.0 ml)

41. Molarity
Calculate the molarity of an aqueous nickel (II) chloride solution containing 28.3 grams of nickel (II) chloride in mL of solution.

42. Molarity
The maximum solubility of lead (II) chromate, PbCrO4, is 4.3 x 10-5 g/L. What is the molarity of a saturated solution of PbCrO4?

43. Molarity
How many moles of sulfuric acid, H2SO4, are contained in 0.80L of a 0.050M solution of sulfuric acid?
How many grams of H2SO4 would be needed to make this solution?

44. Dilution
If we take a more concentrated solution we can dilute it to a lower concentration by adding water to it.
We determine the concentration (molarity) of the diluted solution by using the following formula.
M1V1 = M2V2

45. Dilution
Calculate the concentration of the resulting solution when enough water is added to 250.0mL of 0.60M NaOH to make 300.0mL of solution?

46. Dilution
How much water would need to be added to 125mL of a 1.50M solution of HCl to dilute the solution to a concentration of 0.570M?

47. Density
An understanding of density is often necessary in solving various problems.
Density is a ratio of mass to volume and therefore can be used in the conversion of mass to volume or volume to mass.

48. Mass Percent
An understanding of mass percent is often necessary in solving various problems.
Mass percent indicates the percentage of a particular substance in a mixture.

49. Aniline, C6H5NH2, a key ingredient in the preparation of dyes for fabrics, is produced by the reaction of C6H5Cl with a solution containing 28.2% NH3 by mass. If the density of the NH3 solution is 0.899g/cm3. What mass of NH3 is needed to prepare 125mL of the ammonia solution?
aniline

50. Aniline, C6H5NH2, a key ingredient in the preparation of dyes for fabrics, is produced by the reaction of C6H5Cl with a solution containing 28.2% NH3 by mass. If the density of the NH3 solution is 0.899g/cm3. What mass of NH3 is needed to prepare 125mL of the ammonia solution?

51. Stoichiometry: Calculations based on balanced equations.
We use the balanced equation to determine a mole ratio.
Then we use “Moles to Move”.

52. Stoichiometry: Calculations based on balanced equations.
How many moles of Al2I6 are produced from 0.40 mol Al? → +

53. Stoichiometry: Calculations based on balanced equations.
Calculate the moles of oxygen produced by the thermal decomposition of 100.0g of potassium chlorate.

54. Stoichiometry: Calculations based on balanced equations.
Calculate the moles of oxygen produced by the thermal decomposition of 100.0g of potassium chlorate.
Write the equation for this reaction.

55. Calculate the moles of oxygen produced by the thermal decomposition of 100.0g of potassium chlorate.
Write the equation for this reaction.
2KClO3 → 2KCl + 3O2

56. Calculate the moles of oxygen produced by the thermal decomposition of 100.0g of potassium chlorate.
2KClO3 → 2KCl + 3O2

57. The antacid milk of magnesia contains Mg(OH)2
The antacid milk of magnesia contains Mg(OH)2. What mass of NaOH would be needed to produce 16g of Mg(OH)2? MgCl2 + 2NaOH → Mg(OH)2 + 2NaCl .

58. The antacid milk of magnesia contains Mg(OH)2
The antacid milk of magnesia contains Mg(OH)2. What mass of NaOH would be needed to produce 16g of Mg(OH)2?
MgCl2 + 2NaOH → Mg(OH)2 + 2NaCl

59. What mass of oxygen is required to burn 702g of octane?

60. What mass of oxygen is required to burn 702g of octane?
Write the balanced equation for this reaction.

61. What mass of oxygen is required to burn 702g of octane?
2C8H O2 → 16CO2 + 18H2O

62. What volume of 0.750M HCl can be made from 25.0g of NaCl?
NaCl + H2SO4 → HCl + NaHSO4

63. What volume of 0. 2089M KI solution reacts with 43. 88mL of 0
What volume of M KI solution reacts with 43.88mL of M Cu(NO3)2?
2Cu(NO3)2 + 4KI → 2CuI + I2 + 4KNO3

64. Percentage Yield actual yield Percent Yield = X 100 theoretical yield
Percentage yield can be a part of stoichiometry problems

65. Percentage Yield
1.274g of CuSO4 produces 0.392g of Cu. What is the percentage yield?
CuSO4 + Zn → Cu + ZnSO4 →

66. Percentage Yield
1.274g of CuSO4 produces 0.392g of Cu. What is the percentage yield?
CuSO4 + Zn → Cu + ZnSO4

67. Limiting Reagents
A limiting reagent (reactant) is the reactant that is used up in a chemical reaction.
All other reactants are said to be in excess.

69. NaHCO3 + HC2H3O2 → NaC2H3O2 + H2CO3
Limiting Reagent
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2CO3
195g NaHCO3 and 152ml 3.0M HC2H3O2

70. NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Limiting Reagent
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
195g NaHCO3 and 152ml 3.0M HC2H3O2

71. NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Limiting Reagent
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
195g NaHCO3 and 152ml 3.0M HC2H3O2
Which reactant is limiting?

72. NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Limiting Reagent
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
195g NaHCO3 and 152ml 3.0M HC2H3O2
Which reactant is limiting?
How many grams of CO2 are produced?

73. NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Limiting Reagent
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
195g NaHCO3 and 152ml 3.0M HC2H3O2
Which reactant is limiting?
How many grams of CO2 are produced?
How many grams of NaHCO3 remain after the reaction?

74. NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Limiting Reagent
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
195g NaHCO3 and 152ml 3.0M HC2H3O2
How many grams of NaHCO3 remain after the reaction?

75. A mixture of 5. 0g H2 and 10. 0g of O2 is ignited forming water
A mixture of 5.0g H2 and 10.0g of O2 is ignited forming water. How much water will the reaction produce?

76. Titration
Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a reactant.
Because volume measurements play a key role in titration, it is also known as volumetric analysis.
A reagent, called the titrant, is placed in a calibrated buret and reacted with another solution.
One of the solutions is of known concentration (a standard solution). It is used to react with a solution whose concentration is not known.
An indicator is used to identify the endpoint of the reaction. The point at which the reaction is complete. The endpoint is often indicated by a permanent change in color due to the indicator.

77. Titration
Before endpoint
Endpoint
Overshoot

78. Titration (Acid – Base)

79. 5105g NaOH is dissolved in water and titrated to an endpoint with 48
0.5105g NaOH is dissolved in water and titrated to an endpoint with mL of HCl. What is the concentration of HCl?
NaOH + HCl → NaCl + H2O

80. 5H2C2O4 + 2KMnO4 + 3H2SO4 → 2MnSO4 + K2SO4 + 10CO2 + 8H2O
A solution of 20.00mL of oxalic acid was titrated to an endpoint with 23.23mL of M potassium permanganate. What is the concentration of the oxalic acid solution.
5H2C2O4 + 2KMnO4 + 3H2SO4 → 2MnSO4 + K2SO4 + 10CO2 + 8H2O

81. Ca(OH)2 + 2HC2H3O2 → Ca(C2H3O2)2 + 2H2O
How many grams of a sample containing 75.0% calcium hydroxide by mass is required to react with the acetic acid in 25.0mL of a solution having a density of g/mL and containing 58.0% acetic acid by mass?
Ca(OH)2 + 2HC2H3O2 → Ca(C2H3O2)2 + 2H2O