1. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Mass Relationships By
Doba Jackson, Ph.D.
Copyright © 2010 Pearson Prentice Hall, Inc.

2. Balancing Chemical Equations
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Balancing Chemical Equations
A balanced chemical equation shows that the law of conservation of mass is adhered to.
In a balanced chemical equation, the numbers and kinds of atoms on both sides of the reaction arrow are identical.
2NaCl(s)
2Na(s) + Cl2(g)
A chemical reaction can be thought of as a rearrangement of the atoms to form new compounds.
left side:
2 Na
2 Cl
right side:
2 Na
2 Cl
Copyright © 2010 Pearson Prentice Hall, Inc.

3. Chemical Symbols on a Different Level
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Symbols on a Different Level
2H2O(l)
2H2(g) + O2(g)
microscopic:
2 molecules of hydrogen gas react with 1 molecule of oxygen gas to yield 2 molecules of liquid water.
Copyright © 2010 Pearson Prentice Hall, Inc.

4. Chemical Symbols on a Different Level
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Symbols on a Different Level
2H2O(l)
2H2(g) + O2(g)
microscopic:
2 molecules of hydrogen gas react with 1 molecule of oxygen gas to yield 2 molecules of liquid water.
macroscopic:
0.56 kg of hydrogen gas react with 4.44 kg of oxygen gas to yield 5.00 kg of liquid water.
Copyright © 2010 Pearson Prentice Hall, Inc.

5. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
How many grams of each reactant is needed and
how many grams of the product are expected?
Copyright © 2010 Pearson Prentice Hall, Inc.

6. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
Molecular Mass: Sum of atomic masses of all atoms in a molecule.
Formula Mass: Sum of atomic masses of all atoms in a formula unit of any compound, molecular or ionic.
C2H4:
2(12.0 amu) + 4(1.0 amu) = 28.0 amu
HCl:
1.0 amu amu = 36.5 amu
Copyright © 2010 Pearson Prentice Hall, Inc.

7. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
One mole of any substance is equivalent to its molecular or formula mass.
1 mole = 28.0 g
C2H4:
6.022 x 1023 molecules = 28.0 g
1 mole = 36.5 g
6.022 x 1023 molecules = 36.5 g
HCl:
Copyright © 2010 Pearson Prentice Hall, Inc.

8. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
How many moles of chlorine gas, Cl2, are in 25.0 g?
25.0 g Cl2
1 mol Cl2 x
= mol Cl2
70.9 g Cl2
Copyright © 2010 Pearson Prentice Hall, Inc.

9. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
How many grams of sodium hypochlorite, NaOCl, are in mol?
0.705 mol NaOCl
74.5 g NaOCl x
= 52.5 g NaOCl
1 mol NaOCl
Na = amu
O = amu
Cl = amu
Copyright © 2010 Pearson Prentice Hall, Inc.

10. Law of Constant Composition
Chemical Formula
2Hg
2HgO O2 +
Chemical Equation
HgO
Joseph Priestly isolated oxygen in 1774 by heating mercury(II) oxide.
Mass percentage
of mercury
Mass percentage
of oxygen

11. Empirical and Molecular Formula’s
Mass percentage
of mercury
Mass percentage
of oxygen
HgO contains one mole of Hg per mole of oxygen
Empirical formula- a formula that shows the ratio of
each element repective to each other. Does not
always represent the actual formula.

12. Analysis of a g sample of a liquid compound composed of carbon, hydrogen, and nitrogen showed it contain 7.34 g C, 1.85 g H, and 2.85 g N. What is the percent composition of this compound?

13. Aspirin is a compound with the molecular formula C9H8O4
Aspirin is a compound with the molecular formula C9H8O4. What is the percent composition of each element ?

14. Determining Empirical formula’s

15. A sample of the black mineral hematite, an oxide of iron found in many iron ores, contains g of iron and g of oxygen. What is the empirical formula of hematite?

16. What is the empirical formula of a compound if a sample contains 0
What is the empirical formula of a compound if a sample contains g of nitrogen and g of oxygen?

17. Concentrations of Reactants in Solution: Molarity
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Concentrations of Reactants in Solution: Molarity
Molarity (M): The number of moles of a substance dissolved in each liter of solution. In practice, a solution of known molarity is prepared by weighing an appropriate amount of solute, placing it in a container called a volumetric flask, and adding enough solvent until an accurately calibrated final volume is reached.
Solution: A homogeneous mixture.
Solute: The dissolved substance in a solution.
Solvent: The major component in a solution.
It’s the volume of solution that’s needed and not simply the volume of water (assuming water is the solvent).
Copyright © 2010 Pearson Prentice Hall, Inc.

18. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Copyright © 2010 Pearson Prentice Hall, Inc.

19. Concentrations of Reactants in Solution: Molarity
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Concentrations of Reactants in Solution: Molarity
Molarity converts between mole of solute and liters of solution:
Moles of solute
Liters of solution
Molarity =
1.00 mol of sodium chloride placed in enough water to make 1.00 L of solution would have a concentration equal to:
1.00 mol
mol
= 1.00
or 1.00 M
1.00 L L
Copyright © 2010 Pearson Prentice Hall, Inc.

20. Concentrations of Reactants in Solution: Molarity
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Concentrations of Reactants in Solution: Molarity
How many grams of solute would you use to prepare 1.50 L of M glucose, C6H12O6?
Molar mass C6H12O6 = g/mol
1.50 L
0.250 mol x
= mol
1 L
0.275 mol
180.0 g x
= 49.5 g
1 mol
Copyright © 2010 Pearson Prentice Hall, Inc.

21. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Copyright © 2010 Pearson Prentice Hall, Inc.

22. Diluting Concentrated Solutions
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Diluting Concentrated Solutions
dilute solution
concentrated solution + solvent
initial
final
Mi x Vi = Mf x Vf
Since the number of moles of solute remains constant, all that changes is the volume of solution by adding more solvent.
Molarity x Volume (in liters) = moles
Since the conversion between liters and milliliters is multiplicative, the volume units do not have to be liters. All that is necessary is that the volume units are the same.
Copyright © 2010 Pearson Prentice Hall, Inc.

23. Diluting Concentrated Solutions
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Diluting Concentrated Solutions
Sulfuric acid is normally purchased at a concentration of 18.0 M. How would you prepare mL of M aqueous H2SO4?
Mi = 18.0 M Mf = M
Vi = ? mL Vf = mL
Add acid to water! Mi Mf Vf
0.500 M
250.0 mL
Vi = x = x
= 6.94 mL
18.0 M
Add 6.94 mL 18.0 M sulfuric acid to enough water to make mL of M solution.
Copyright © 2010 Pearson Prentice Hall, Inc.

24. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
Stoichiometry: The relative proportions in which elements form compounds or in which substances react.
aA + bB
cC + dD
Grams of A
Moles of A
Moles of B
Grams of B
Definition from the Oxford Dictionary of Chemistry, Oxford University Press, 2000.
Its origin is Greek for “element” “measure.”
“grams-to-moles-to-moles-to-grams”
You need the coefficients from the balanced chemical equation.
You can relate any of the substances in the chemical equation to each other.
Molar Mass of A
Mole Ratio Between A and B (Coefficients)
Molar Mass of B
Copyright © 2010 Pearson Prentice Hall, Inc.

25. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
Aqueous solutions of sodium hypochlorite (NaOCl), best known as household bleach, are prepared by reaction of sodium hydroxide with chlorine gas:
2NaOH(aq) + Cl2(g)
NaOCl(aq) + NaCl(aq) + H2O(l)
How many grams of NaOH are needed to react with 25.0 g Cl2?
Grams of
Cl2
Moles of
Cl2
Moles of
NaOH
Grams of
NaOH
Molar Mass
Mole Ratio
Molar Mass
Copyright © 2010 Pearson Prentice Hall, Inc.

26. Chemical Arithmetic: Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Chemical Arithmetic: Stoichiometry
Aqueous solutions of sodium hypochlorite (NaOCl), best known as household bleach, are prepared by reaction of sodium hydroxide with chlorine gas:
2NaOH(aq) + Cl2(g)
NaOCl(aq) + NaCl(aq) + H2O(l)
How many grams of NaOH are needed to react with 25.0 g Cl2?
25.0 g Cl2
Remind students about significant figures.
1 mol Cl2
2 mol NaOH
40.0 g NaOH x x x
70.9 g Cl2
1 mol Cl2
1 mol NaOH
= 28.2 g NaOH
Copyright © 2010 Pearson Prentice Hall, Inc.

27. Yields of Chemical Reactions
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Yields of Chemical Reactions
Actual Yield:
Theoretical Yield:
The amount actually formed in a reaction.
The amount predicted by calculations.
Actual yield of product
Theoretical yield of product
Percent Yield =
x 100%
Maximum percent yield is 100%.
Copyright © 2010 Pearson Prentice Hall, Inc.

28. Reactions with Limiting Amounts of Reactants
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Reactions with Limiting Amounts of Reactants
Limiting Reactant: The reactant that is present in limiting amount. The extent to which a chemical reaction takes place depends on the limiting reactant.
Excess Reactant: Any of the other reactants still present after determination of the limiting reactant.
C2H4O(aq) H2O(l)
C2H6O2(l)
Copyright © 2010 Pearson Prentice Hall, Inc.

29. Reactions with Limiting Amounts of Reactants
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Reactions with Limiting Amounts of Reactants
At a high temperature, ethylene oxide reacts with water to form ethylene glycol, which is an automobile antifreeze and a starting material in the preparation of polyester polymers:
C2H4O(aq) H2O(l)
C2H6O2(l)
Copyright © 2010 Pearson Prentice Hall, Inc.

30. Problem: Reactions with Limiting Amounts of Reactants
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Problem: Reactions with Limiting Amounts of Reactants
Lithium oxide is used aboard the space shuttle to remove water from the air supply according to the equation:
Li2O(s) + H2O(g)
2LiOH(s)
If 80.0 g of water are to be removed and 65.0 g of Li2O are available, which reactant is limiting? How many grams of excess reactant remain? How many grams of LiOH are produced?
Copyright © 2010 Pearson Prentice Hall, Inc.

31. Reactions with Limiting Amounts of Reactants
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Reactions with Limiting Amounts of Reactants
Li2O(s) + H2O(g)
2LiOH(s)
Which reactant is limiting?
Amount of H2O that will react with 65.0 g Li2O:
65.0 g Li2O
1 mol Li2O
1 mol H2O x x
= 2.17 moles H2O
29.9 g Li2O
1 mol Li2O
Amount of H2O given:
80.0 g H2O
1 mol H2O x
= 4.44 moles H2O
18.0 g H2O
Li2O is limiting
Copyright © 2010 Pearson Prentice Hall, Inc.

32. Reactions with Limiting Amounts of Reactants
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Reactions with Limiting Amounts of Reactants
Li2O(s) + H2O(g)
2LiOH(s)
How many grams of excess H2O remain?
2.17 mol H2O
18.0 g H2O x
= 39.1 g H2O (consumed)
1 mol H2O
80.0 g H2O g H2O = 40.9 g H2O
initial
consumed
remaining
Copyright © 2010 Pearson Prentice Hall, Inc.

33. Reactions with Limiting Amounts of Reactants
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Reactions with Limiting Amounts of Reactants
Li2O(s) + H2O(g)
2LiOH(s)
How many grams of LiOH are produced?
2.17 mol H2O
2 mol LiOH
23.9 g LiOH x x
= 104 g LiOH
1 mol H2O
1 mol LiOH
Copyright © 2010 Pearson Prentice Hall, Inc.

34. Solution Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Solution Stoichiometry
aA + bB
cC + dD
Volume of
Solution of A
Moles of A
Moles of B
Volume of
Solution of B
Molarity of A
Mole Ratio Between A and B (Coefficients)
Molar Mass of B
These problems still come back to moles.
Copyright © 2010 Pearson Prentice Hall, Inc.

35. Solution Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Solution Stoichiometry
What volume of M H2SO4 is needed to react with 50.0 mL of M NaOH?
H2SO4(aq) + 2NaOH(aq)
Na2SO4(aq) + 2H2O(l)
Volume of
Solution of H2SO4
Moles of
H2SO4
Moles of
NaOH
Volume of
Solution of NaOH
Note that the method is very similar to that for mass stoichiometry.
Molarity of H2SO4
Mole Ratio Between H2SO4 and NaOH
Molarity of NaOH
Copyright © 2010 Pearson Prentice Hall, Inc.

36. Solution Stoichiometry
Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Solution Stoichiometry
H2SO4(aq) + 2NaOH(aq)
Na2SO4(aq) + 2H2O(l)
Moles of NaOH available:
50.0 mL NaOH
0.100 mol
1 L x x
= mol NaOH
1 L
1000 mL
Volume of H2SO4 needed:
mol NaOH
1 mol H2SO4
1 L solution
1000 mL x x x
2 mol NaOH
0.250 mol H2SO4
1 L
10.0 mL solution (0.250 M H2SO4)
Copyright © 2010 Pearson Prentice Hall, Inc.

37. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Titration
Titration: A procedure for determining the concentration of a solution by allowing a carefully measured volume to react with a solution of another substance (the standard solution) whose concentration is known.
HCl(aq) + NaOH(aq)
NaCl(aq) + 2H2O(l)
Once the reaction is complete you can calculate the concentration of the unknown solution.
How can you tell when the reaction is complete?
Copyright © 2010 Pearson Prentice Hall, Inc.

38. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Titration
standard solution
(known concentration)
buret
Erlenmeyer
flask
unknown concentration solution
An indicator is added which changes color once the reaction is complete
Copyright © 2010 Pearson Prentice Hall, Inc.

39. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Phenolphthalein is commonly used for HCl-NaOH titrations. It turns red (pink) in slightly basic solutions.
Copyright © 2010 Pearson Prentice Hall, Inc.

40. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Titration
48.6 mL of a M NaOH solution is needed to react with 20.0 mL of an unknown HCl concentration. What is the concentration of the HCl solution?
HCl(aq) + NaOH(aq)
NaCl(aq) + 2H2O(l)
Volume of
Solution of NaOH
Moles of
NaOH
Moles of
HCl
Volume of
Solution of HCl
Molarity of NaOH
Mole Ratio Between NaOH and HCl
Molarity of HCl
Copyright © 2010 Pearson Prentice Hall, Inc.

41. Chapter 6: Mass Relationships in Chemical Reactions
9/12/2018
Titration
HCl(aq) + NaOH(aq)
NaCl(aq) + 2H2O(l)
Moles of NaOH available:
48.6 mL NaOH
0.100 mol
1 L x x
= mol NaOH
1 L
1000 mL
Moles of HCl reacted:
mol NaOH
1 mol HCl x
= mol HCl
1 mol NaOH
Concentration of HCl solution:
mol HCl
1000 mL x
= M HCl
20.0 mL solution
1 L
Copyright © 2010 Pearson Prentice Hall, Inc.

42. Problem: What is the molecular mass of table sugar (sucrose, C12H22O11), and what is its molar mass in g/mol?

43. Problem: How many moles of sucrose are in a tablespoon of sugar containing 2.85 g?

44. Problem: How many grams are in 0
Problem: How many grams are in mol of NaHCO3, the main ingredient of Alka-Seltzer tablets?

45. Problem: Aqueous solutions of sodium hypochlorite (NaOCl, household bleach) are prepared by reaction of sodium hydroxide with chlorine. How many grams of NaOH are needed to react with 25.0 g of Cl2?

46. Problem: Cisplatin, an anticancer agent used for the treatment of solid tumors, is prepared by the reaction of ammonia with potassium tetrachloroplatinate. Assume that 10.0 g of K2PtCl4 and 10.0 g of NH3 are allowed to react.       (a) Which reactant is limiting, and which is in excess? (b) How many grams of the excess reactant are consumed, and how many grams remain? (c) How many grams of cisplatin are formed?