Topic # 8 Descriptive Chemistry of reactions and Chemical ...



Descriptive Chemistry,

Formula Writing and Nomenclature

___________ Homework:

Exam Date:

Free Response ~ ___________

Multiple Choice ~ ___________

Textbook: Read Chapter 4 Nomenclature P.84-111

Read p. 577-579 Section 18.2 Assigning Oxidation Numbers

Read Chapter 7 Chemical Reactions: An Introduction P. 192-199

Highlights: P.98-99 Read summary for naming binary compounds. Self-check Exercises 18.2 p. 579

Descriptive Chemistry of reactions and Chemical Formulas Student Outline

Descriptive chemistry involves the rules for writing formulas of compounds and writing different types of chemical reactions. Balancing equations is introduced and studied more in the topic of mole concept. Dalton first described that elements within a compound occur in specific ratios that do not change.

Chemical Equation-

Parts of a chemical equation

1. reactants

• products

• yield sign

• double arrows

• arrow up at end of an equation^

• arrow down at the end of equation

• ( over the arrows

• heat in kilojoules at the beginning of the reaction(with the reactants) means endothermic

• heat in kilojoules at the end of the reaction( with the products) means exothermic

• significance of coefficients in balancing equations

• (s) = solid, (l) liquid, (g) gas, (aq) aqueous (homogeneous mixture with water /solution/hydrated)

• catalyst in a reaction

Types of Chemical Reactions

|TYPE OF REACTION |DESCRIPTION AND GENERAL REACTION |

| |Atoms of elements combine to form a compound |

| | |

|Synthesis |4 Fe + 3 O2 ( 2 Fe2O3 |

| |Compound is broken down into its component elements or simpler compounds |

| | |

| |2 HgO ( 2 Hg + O2 |

|Decomposition | |

| |A single element reacts with a compound to take the place of an element of |

| |similar character. This replacement results in the formation of a new |

| |compound and a new free element. |

|Single Replacement | |

| |Cu + 2 AgNO3 ( Cu(NO3)2 + 2Ag |

| |Two compounds react to produce two new compounds (elements switch places) |

| | |

|Double Replacement |AgCl + KNO3 ( AgNO3 + KCl |

Assigning Oxidation States:

1. 1st element in a compound (the one on the left which is typically a metal or the element that is MORE likely to lose e-) usually assumes a POSITIVE oxidation state.

Exceptions:

• (OH)-1 … oxygen = -2 and hydrogen = +1

• NH3 & (NH4)+1 … nitrogen = -3 and hydrogen = +1

• Organic compounds: CH4 … C= -4 and hydrogen = +1

• Oxygen is ALMOST ALWAYS = -2 Except: 1. OF2 …O= +2 and F = -1 (F has a greater electronegativity)

2. Peroxides: H2O2 ….H = +1 and O -1

3. Na2O2… Na= +1 and O = -1

2. if there is more than one oxidation choice

a. stock system: assigning roman numerals for the oxidation state… (example +1 = I….+4= IV…..

+7= VII) ( the roman numeral IS the oxidation # … not the CHOICE

b. ** Old latin/ standard system – using suffix to designated the higher or lower of 2 oxidation choices.

“ous” = lower choice…. “ic” = higher choice.

Prefixes include: Iron = Ferr… Lead = Plumb…Copper= cupr Examples: Fe+2 ferrous; Fe+3 ferric;

Example: Cu+1=cuprous; Cu+2=cupric

c. complicated assignments – the need to figure out the correct choice using other information in the formula. When assigning oxidation states … you can assume the overall charge of the compound = 0 .. unless designated with an ion charge ( + or -)

3. If there are more than 2 elements in a compound … non binary compounds … must use 1st last middle rule to identify oxidation states. ** be careful of SHARED OXIDATION CHARGES **

4. Assigning oxidation states to ions … such as polyatomic ions… overall charge of the ion is always noted.

5. Free elements or diatomic molecules .. can exist alone .. uncombined always have an oxidation state of 0

Diatomic molecules: elements that always occur in pairs when not in a chemical compound

** REMEMBER~ BrINClHOF

6. Be careful of Dimercury … chart E …+2

Naming Chemical Compounds

1. Ionic Compounds:

binary compounds – metal written first with “ide” ending on the nonmetal

exceptions: cyanide, hydroxide

A. ternary compounds – metal(+) and polyatomic(-)second name ends in “ate” or “ite”. Use chart E.

OR polyatomic ion(+) and nonmetal(-)second name ends in “ide”

C. transition elements with multiple oxidation states – use the stock system including a Roman numeral designating

the oxidation state of the first element.

D. Standard system can be used with “ic” or “ous” endings

2. Covalent compounds

A. Stock system used with roman numerals designates the oxidation state of the first element

a. CO2 carbon IV oxide

B. Standard system used with prefixes denoting number of atoms for that element NOT the oxidation state; used more commonly with covalent compounds

a. CO2 carbon dioxide (Prefixes: mono = 1 di = 2 tri = 3 tetra = 4 penta = 5)

Writing Chemical Formulas

1. Ionic Compounds:

a. Binary – criss cross method

b. Ternary – criss cross method; use parenthesis around polyatomic ions if subscript is more than one:

c. Stock System – criss cross method (All types reduce subscripts to empirical formula)

2. Covalent Compounds:

a. Binary (prefix) – no criss crossing

b. Binary (stock system) – criss cross method (All types reduce to empirical formula)

VOCABULARY

Chemical Equation

reactants

products

yields

double arrows

( over the arrows

exothermic

endothermic

precipitate

coefficients

Synthesis

Decomposition

Single Replacement

Double Replacement

Valence Electrons

Oxidation States

Chemical symbol

Chemical Formula

Molecular Formula

Empirical Formula

Binary Compound

Ternary Compound

stock system

standard system

ion charge

oxidation states.

Free elements

diatomic molecules

Descriptive Chemistry and Chemical Formulas Homework

I. Writing oxidation numbers and formulas

A. Give the correct/most probable oxidation state that each element or polyatomic ion will assume when in a compound

|Element/ion |Oxidation state |Element/ion |Oxidation state |

|1. Calcium | |7. sulfide | |

|2. Fluoride | |8. aluminum | |

|3. Sodium | |9. Chloride | |

|4. Zinc | |10. Krypton | |

|5. Copper I | |11. Strontium | |

|6. Cobalt III | |12. Sulfite | |

B. For each of the molecular formulas give the correct empirical formula

|Molecular Formula |Empirical Formula |

|1. N2O4 | |

|2. C6H8O6 | |

|3. C2H6 | |

|4. CH4 | |

|5. Hg2I2 | |

|6. C8H18 | |

C. For each of the following compounds tell the number of each atom present and the total number of formula units in the compound

|Chemical Formula |Number of atoms one formula unit |Number of formula units |Total number of atoms represented |

|1. Ag2CO3 | | | |

|2. 2Fe(NO3)2 | | | |

|3. 4AlBr3 | | | |

|4. 6Ba(PO4)2 | | | |

|5. 3CH3COOH | | | |

D. Writing Oxidation Numbers and names of compounds

For each of the following give the oxidation state of each element in the compound based on the given formula and write the correct IUPAC name for that compound.

|Compounds |oxidation state |oxidation state last |IUPAC Name of compound |

|(IONIC) |first element |element | |

|1. Fe2O3 | | | |

|2. CoF2 | | | |

|3. NiS | | | |

|4. MnF3 | | | |

|Compounds |oxidation state |oxidation state last |IUPAC Names of compounds |

|(COVALENT) |first element |element |(Use both stock and standard naming) |

|5. N2O | | | |

|6. N2O3 | | | |

|7. CO2 | | | |

|8. CCl4 | | | |

|9. SO3 | | | |

|10. CS2 | | | |

|Polyatomic |oxidation state first |oxidation state last |Name of polyatomic ion |

|ion |element |element |(use Table E) |

|11. SO3-2 | | | |

|12. NO3-1 | | | |

|13. ClO2-1 | | | |

|14. ClO4-1 | | | |

| 15. OH-1 | | | |

|16. NH4+1 | | | |

|Ternary |oxidation state |oxidation state last |oxidation state |IUPAC Name of compound |

|compounds |first element |element |middle element | |

|17. Al(ClO)3 | | | | |

|18. NH4Cl | | | | |

|19. Ca(MnO4)2 | | | | |

|20. CuSO4 | | | | |

|21. Ba(CN)2 | | | | |

|22. Fe(NO3)3 | | | | |

Textbook page 109

29

b) _________________________ d) ____________________________

f) _________________________ h)____________________________

j) _________________________ l) ____________________________

III. Naming compounds

Textbook Page 108

6. b) __________________________________

d) ___________________________________

e) ___________________________________

Page 111

45.b)_________________________________

d) _______________________________

f) _______________________________

46. b) _______________________________

d) _______________________________

f) ________________________________

47. b) ________________________________

d) ________________________________

f) ________________________________

IV. Writing Chemical Reactions

For each of the following equations identify the:

a) type of reaction on the line after the reaction.

b) write the oxidation states above all elements in the box above the equation

1. Fe + S ( FeS Type:__________________

2. Zn + CuSO4 ( ZnSO4 + Cu Type:__________________

3. AgNO3 + NaBr ( NaNO3 + AgBr Type: __________________

4. 2KClO3 ( 2KCl + 3O2 Type:__________________

5. 2HgO ( 2Hg + O2 Type:__________________

6. 4Al + 3O2 ( 2Al2O3 Type:__________________

7. K2CO3 + BaCl2 ( 2KCl + BaCO3 Type:__________________

8. CaO + MgCl2 ( MgO + CaCl2 Type:__________________

9. 2Al + Fe2O3 ( Al2O3 + 2Fe Type:__________________

Writing chemical reactions

Textbook page 209

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