CHEMISTRY REGENTS REVIEW

SPRING 2012

THE MOLE AND STOICHIOMETRY

Week # 3

REGENTS TEXTBOOK: CHAPTER 10 & 12

HONORS TEXTBOOK: CHAPTER 11 & 12

BARRONS REV. BOOK: CHAPTER 4

Section I

Moles and Stoichiometry

Chemical Formulas

  1. Chemical Formula - statement in chemical symbols that represents the composition of a substance.
  2. Symbol - represents a single atom of an element or a mole of that element (6.02 X 1023 atoms)
  3. Subscripts - applies to the element that precedes it
  4. No subscript - 1 is understood
  5. allows us to determine the ratio of atoms which combine in a compound
  6. Qualitative analysis - finds out the kinds of elements in a substance
  7. Quantitative analysis - determines how much of each element is present
  8. Empirical Formula - simplest ratio in which the atoms combine to form a compound
  9. use subscripts to determine the least common factor
  10. Molecular Formula - the total number of atoms of each element in one molecule of a substance
  11. Structural Formula - shows how atoms are joined together in a molecule
  12. Ionic Compounds - only exist as empirical formulas
  13. the ionic charge is carried as a superscript
  14. Positive ions are called cations
  15. Negative ions are called anions
  16. The total charge of an ionic compound must equal 0

1.  ex. Mg2+ + F- ® Mg2+ F-2

  1. this is also true of polyatomic ions (treat a PAI as a single ion with its charge)
  2. In simple ions (one atom), the oxidation number is equal to the charge on the ion (periodic table)
  3. The oxidation number of oxygen is -2, except in peroxides when it is -1
  4. The oxidation number of hydrogen is +1, except in hydrides when it is -1
  5. Naming Compounds
  6. Binary compounds - the less electronegative element is named first and the second element ends in ide.
  7. Ex. MgCl2 is magnesium chloride
  8. Ternary compounds (containing polyatomic ions) - name the element, then the polyatomic ion
  9. Ex. MgSO4 is magnesium sulfate
  10. Ex: (NH4)2CO3 is ammonium carbonate
  11. Acids - contains hydrogen with a nonmetal or polyatomic ion
  12. Binary acid - use prefix hydro with the nonmetal and change the end to ic.
  13. Ex. HCL is Hydrochloric Acid
  14. Ternary acid (containing polyatomic ion) -
  15. ion ends in ate, use ic ending
  16. Ex. H2SO4 is sulfuric acid
  17. ion ends in ite, use ous ending
  18. Ex. H2SO3 is sulfurous acid
  19. Metals with multiple oxidation states: New Format - Stock System
  20. Name of element, roman numeral of ionic charge in parenthesis
  21. Molecular Substances
  22. Prefixes are used in naming the nonmetal molecules
  23. If first element is 1, then do not use a prefix for it, but you must use a prefix for the second element at all times (mono, di, tri, tetra,)
  24. Ex. CCl4 is carbon tetrachloride
  25. If there is more than one element for the first element in the formula, then use the prefix for the first element also.
  26. ex. N2O5 – dinitrogen pentoxide

Stoichiometry

  1. The study of the quantitative relationships that can be derived from formulas and equations.
  2. Formula Information:
  3. elements present in a compound
  4. relative number of atoms of each element in a compound
  5. the number of atoms of each element present in 1 molecule of the substance
  6. the number of moles of atoms of each element present in 1 mole of the substance.
  7. Gram Atomic Mass - the quantity of the element which has a mass in grams equal to the atomic mass
  8. equals 1 mole of the element
  9. equals 6.02 X 1023 atoms of the element
  10. occupies a volume of 22.4L at STP if it is a gas
  11. Gram Formula Mass - the sum of all the gram atomic masses in the formula of the substance
  12. equals 1 mole of the compound
  13. equals 6.02 X 1023 molecules of the compound
  14. occupies a volume of 22.4L at STP if it is a gas
  15. H2O

Element / Atomic Mass / # of Atoms/Formula / Product
H / 1 / 2 / 2
O / 16 / 1 / 16
Total Mass = / 18
  1. Ca(OH)2.

Element / Atomic Mass / # of Atoms/Formula / Product
Ca / 40 / 1 / 40
O / 16 / 2 / 32
H / 1 / 2 / 2
Total Mass = / 74
  1. Mole Relationships – 1 mole of any substance = the GFM
  2. Percentage Composition - the percentage by mass of the elements in a compound
  3. Formula : Mass of element in sample

Total mass of sample

  1. H2O: 2g/18g = 11.1%

16g/18g = 88.9%

  1. Ca(OH)2: 40g/74g = 54.1%

2g/74g = 2.7%

32g/74g = 43.2%

= 100%

Stoichiometry II

  1. Mole – Mole Problems
  2. Set up a ratio of moles of substances in the balanced equation to the actual moles

MOLE INTERPRETATION

·  Gram atomic mass

·  Gram formula mass [ mole-mass]

·  Molar volume of a gas

STOICHIOMETRY

·  Calculate mole-mole problems

·  Determine the number of moles of a substance given mass

·  Interpret balanced chemical equations in terms of conservation of mass and energy

·  Calculate percent composition

·  Volume-volume problems if both reactants and products are gases

Section II- Vocabulary

Avogadro’s number______

Empirical formula______

Gram formula weight______

Gram molecular weight______

Molar Mass______

Molar Volume______

Mole______

Mole Ratio______

Standard temperature and pressure______

Section II

Moles and Stoichiometry Major Points

1.  What is the definition of a mole?

2.  What is Avogadro’s number?

3.  Write the formula to convert grams to moles.

4.  How many moles is 10.0 grams of hydrogen gas?

5.  Write the formula to convert liters to moles.

6.  How many moles, at STP, is 33 liters of carbon dioxide gas?

7.  How are compounds named? ( ionic vs. covalent)

8.  How are empirical formulas similar to and different from molecular formulas?

9.  How can we determine the molecular formula, given the empirical formula and the molecular mass of the compound?

10.  What is the Law of Conservation of Mass?

11.  Why is it necessary to balance equations?