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Semester 1 Chemistry Review. DAY 2. Formula Weight. Find the formula weight of aluminum sulfate. Al 2 (SO 4 ) 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. - PowerPoint PPT Presentation
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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