2. Semester 1 Chemistry Review DAY 2

3. 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 + TOTAL342.14 amu

4. 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 TOTAL342.14 amu

5. Answers Al 2 (SO 4 ) 3 is: 15.77 % Aluminum 28.11 % Sulfur 56.12 % Oxygen

6. Mole Conversions A mole is 6.02 x 10 23 of anything. There are 6.02 x 10 23 amus in 1 gram. 53.2 grams of aluminum sulfate is how many moles?

7. Grams to Moles 7.2 moles of Aluminum Sulfate is how many grams.

8. Empirical vs. Molecular Formulas Empirical Formulas are formulas whose subscripts are in their lowest terms. Examples: Anything Ionic - Na 2 SO 4 or CO 2 or CH 2 O

9. 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 - C 6 H 12 O 6 or N 2 O 4

10. 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 : CaSO 4

11. 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.

12. 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.

13. Some things to remember about writing equations: The diatomic elements when they stand alone are always written: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 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.

14. 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.

15. Types of Reactions Composition Decomposition Replacement Ionic (Double Replacement) Combustion

16. Composition Reaction * two or more elements or compounds may combine to form a more complex compound. * Basic form: A + X → AX 2Mg + O 2 → 2MgO

17. Decomposition: * A single compound breaks down into its component parts or simpler compounds. * Basic form: AX → A + X

18. 4 Types of Decomposition RXNS 2 element decomposition 2HgO → 2Hg + O 2 Metallic chlorates, decompose into metallic chlorides and oxygen. 2KClO3 → 2KCl + 3O 2

19. Metallic carbonates, when heated, form metallic oxides and CO 2. CaCO 3 → CaO + CO 2 Most metallic hydroxides, when heated, decompose into metallic oxides and water. Ca(OH) 2 → CaO + H 2 O

20. (Single) Replacement Replacement of a metal in a compound by a more active metal. Fe + CuSO 4 →FeSO 4 + Cu Replacement of nonmetals by more active nonmetals. Cl 2 + 2NaBr →2NaCl + Br 2

21. Ionic (Double Replacement) NaCl + AgNO 3 → NaNO 3 + AgCl HCl + NaOH → NaCl + H 2 O

22. Combustion Hydrocarbon + Oxygen (CxHy) + O 2 → CO 2 + H 2 O (CxHy) + O 2 → CO + H 2 O

23. Grams / Moles / Atoms Grams A Moles A Atoms A Grams B Moles B Atoms B

24. 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?

25. 2HCl + Zn ---> ZnCl 2 + H 2 52.0g HCl 63.2g Zn 52.0g HCl

26. 2HCl + Zn ---> ZnCl 2 + H 2 52.0g HCl 63.2g Zn 52.0g HCl = 1.44 g H 2 = 1.95 g H 2 = 97.2 g ZnCl 2