Semester 1 Chemistry Review

Semester 1 Chemistry Review

DAY 2

Formula Weight

Find the formula weight of

aluminum sulfate.

• Al2(SO4)3

• Al - 2 x 26.98 = 53.96

• S - 3 x 32.06 = 96.18

• O - 12 x 16.00 = 192.00 +

• TOTAL 342.14 amu

Percent Composition

• What is the percent composition of Aluminum, Sulfur, and Oxygen in Aluminum Sulfate?

• Al - 2 x 26.98 = 53.96 / 342.14 x 100• S - 3 x 32.06 = 96.18 / 342.14 x 100 • O - 12 x 16.00 = 192.00 / 342.14 x 100• TOTAL 342.14 amu

Answers

Al2(SO4)3 is:

15.77 % Aluminum

28.11 % Sulfur

56.12 % Oxygen

Mole Conversions

• A mole is 6.02 x 1023 of anything.

• There are 6.02 x 1023 amus in 1 gram.

• 53.2 grams of aluminum sulfate is how many moles?

Grams to Moles

• 7.2 moles of Aluminum Sulfate is how many grams.

Empirical vs. Molecular Formulas

• Empirical Formulas are formulas whose subscripts are in their lowest terms.

• Examples: Anything Ionic - Na2SO4

or CO2 or CH2O

Molecular Formula

• For ionic compounds, their molecular formula is the same as their empirical formula.

• Some covalent molecules have molecular formulas that can be reduced to empirical formulas.

• Examples - C6H12O6 or N2O4

What is the empirical formula for a compound made up of:

• O - 47.04%

• Ca - 29.40%

• S - 23.56%

• = 2.94

• = .7335

• = .7349

• O-4 Ca-1 S-1

• Answer : CaSO4

Chemical Reactions

Equations show:

• 1. the reactants which enter into a reaction.

• 2. the products which are formed by the reaction.

• 3. the amounts of each substance used and

each substance produced.

Two important principles to remember:

• Every chemical compound has a formula which cannot be altered.

• A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed.

Some things to remember about writing equations:

• The diatomic elements when they stand alone are always written:

• H2, N2, O2, F2, Cl2, Br2, I2

• Before beginning to balance an equation, check each formula to see that it is correct. NEVER change a formula during the balancing of an equation.

More Things to Remember:

• Balancing is done by placing coefficients in front of the formulas to insure the same number of atoms of each element on both sides of the arrow.

• The sign, → , means "yields" and shows the direction of the action.

Types of Reactions

• Composition

• Decomposition

• Replacement

• Ionic (Double Replacement)

• Combustion

Composition Reaction

• * two or more elements or compounds may combine to form a more complex compound.

• * Basic form: A + X → AX

• 2Mg + O2 → 2MgO

Decomposition:

• * A single compound breaks down into its component parts or simpler compounds.

• * Basic form: AX → A + X

4 Types of Decomposition RXNS

• 2 element decomposition

• 2HgO → 2Hg + O2

• Metallic chlorates, • decompose into • metallic chlorides and oxygen.

• 2KClO3 → 2KCl + 3O2

• Metallic carbonates, when heated, form metallic oxides and CO2.

• CaCO3 → CaO + CO2

• Most metallic hydroxides, when heated, decompose into metallic oxides and water.

• Ca(OH)2 → CaO + H2O

(Single) Replacement

• Replacement of a metal in a compound by a more active metal.

• Fe + CuSO4 →FeSO4 + Cu

• Replacement of nonmetals by more active nonmetals.

• Cl2 + 2NaBr →2NaCl + Br2

Ionic (Double Replacement)

• NaCl + AgNO3 →

• NaNO3 + AgCl

• HCl + NaOH →

• NaCl + H2O

Combustion

• Hydrocarbon + Oxygen

• (CxHy) + O2 → CO2 + H2O

• (CxHy) + O2 → CO + H2O

Grams / Moles / Atoms

• Grams A Moles A Atoms A

• Grams B Moles B Atoms B

Limiting Reagent Problems

• 52.0g of hydrochloric acid react with 63.2 g of zinc.

• What is the limiting reagent?• How much product is formed?• How much excess remains?

2HCl + Zn ---> ZnCl2 + H2

• 52.0g HCl

• 63.2g Zn

• 52.0g HCl

2HCl + Zn ---> ZnCl2 + H2

• 52.0g HCl

• 63.2g Zn

• 52.0g HCl

= 1.44 g H2

= 1.95 g H2

= 97.2 g

ZnCl2