Lesson 18: POST Pre-Comp Review

Transcription

1 NOTES Name: Date: Class: Box 1: Lesson 18: POST Pre-Comp Review 1. What are some chemical changes you ve observed in your everyday experience? 2. Name 4 changes that usually indicate that a chemical change has occurred: 3. Write the balanced formula equation the following reaction: Solid zinc and aqueous hydrochloric acid (HCl) react to yield hydrogen gas and aqueous zinc chloride. Balancing Chemical Equations: Modern Chemistry Ch. 8 Sec. 1 (pp ). Read through Sample Problems A-D. *Rules are listed on p * Balancing Chemical Equations Definitions: formula unit: the simplest collection of atoms from which ionic compounds formula can be written compound: molecule: aqueous solution: reactant or product is dissolved in water (aq) coefficient: small whole number that appears in front of a formula in a chemical equation mole: the SI base unit used to measure the amount of a substance whose number of particles is the same number of atoms in exactly 12g of carbon-12 ( ) precipitate: a that is produced as a result of a in solution 7 th grade POST Pre-Comp Review 1

2 Balancing Equations Best Practices (see p.257 in textbook) 1. Balance the different types of atoms one at a time. 2. First, balance the atoms of elements that are and that appear only once on each side of the equation. 3. Second, Balance polyatomic ions that appear on both sides of the equation as single units. Look closely to see if these ions are enclosed in parentheses, and count the individual atoms accordingly. 4. Balance atoms after atoms of all the other elements have been balanced. A new trick: Balancing using a fractional co-efficient. Always balance H and O last (lone elements). 1. Na + H2O NaOH + H2 At the end, you ll need to multiply all coefficients by the fraction denominator so all coefficients are whole numbers. 2. Mg + O2 MgO 3. KClO3 KCl + O2 4. C2H6 + O2 CO2 + H2O 7 th grade POST Pre-Comp Review 2

3 PRACTICE: Write balanced chemical equations for each of the following reactions. Include phases if they are mentioned. Hint: The chemical formula for sulfuric acid is H2SO4. 1. When aqueous solutions of sulfuric acid and barium chloride are mixed, barium sulfate precipitates from an aqueous solution of hydrochloric acid. 2. Aluminum sulfate, an ingredient used in water treatment, is made by the reaction of solid aluminum oxide with aqueous sulfuric acid. In addition to aqueous aluminum sulfate, water is also produced. 3. The white paste that some lifeguards run on their noses to prevent sunburn contains the active ingredient zinc oxide. Zinc oxide is made by reacting solid zinc sulfide with oxygen gas. Sulfur dioxide gas is also produced. 4. Nitrogen dioxide gas reacts with liquid water to form aqueous nitric acid (HNO3) and nitrogen monoxide gas. 7 th grade POST Pre-Comp Review 3

4 Solutions: Modern Chemistry Ch.12 sec.1 (pp ). Solutions Definitions: solution: a mixture of two or more substances uniformly dispersed in a single phase soluble: solvent: the (water is the universal solvent) solute: suspension: a heterogeneous mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas; particles are so large that they settle out unless the mixture is constantly stirred or agitated colloid: mixture consisting of tiny particles that are intermediate in size (bigger than particles in a solution, smaller than particles in a suspension); particles remain suspended in a solid, liquid, or gas. Components of Solutions: solute + solvent Solute Solvent (in greater quantity) Solution Examples: solute in solvent Air = O2 in N2 GAS LIQUID Carbonated beverages = CO2 in H2O LIQUID LIQUID LIQUID Vinegar = acetic acid in water LIQUID LIQUID Salt water = NaCl (s) in H2O (l) SOLID SOLID SOLID Steel = Carbon in Iron 7 th grade POST Pre-Comp Review 4

5 Practice: Identifying Solutes and Solvents. (Hint: the solvent is always in the greater amount) 1. Solution: Cup of coffee 2. Solution: Sterling silver 3. Solution: Air 4. Solution: H2SO4 (aq) 5. Solution: Humid air 6. Solution: Dry cleaning chemicals (20% ethane + 75% dichloromethane) 7. Solution: a. solute: 15.6 g LiNO2 b. solvent: 200 ml H2O 8. Situation: Adding 50.2 mg of BaCl2 to 100 ml of H2O. 9. Situation: Removing a grass stain from a pair of pants with ethanol. 10. Situation: Removing nail polish with 75% acetone. 7 th grade POST Pre-Comp Review 5

6 Lewis Structures Definitions: Lewis structure: formulas in which atomic symbols represent nuclei and inner-shell electrons, dashes between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbol represent unshared electrons lone pair: dots next to atomic symbol,, are important for atom to have a full valence shell octet rule: atoms of main-group elements tend to combine in such a way that each atom has electrons in its valence shell, giving it the same electron configuration as. resonance: bonding in molecules or ions that by a Lewis structure single covalent bond: Group 4A C, Si, Ge Group 5A N, P, As, Sb Group 6A O, S, Se, Te, Po Group 7A F, Cl, Br, I # of valence electrons # of electrons needed for a full outer shell (octet rule) # of covalent bonds atom will make # of lone pairs atom will have Basic Lewis Structure 7 th grade POST Pre-Comp Review 6

7 PRACTICE: Draw the Lewis structure for each of the following compounds. 1. H2O 2. CH4 3. CH3OH 4. HCl 5. CH3I 6. CO2 7 th grade POST Pre-Comp Review 7

8 PRACTICE: Using your knowledge of covalent bonding and Lewis structures, answer the questions below. 1. Which element is composed of molecules that each contain a multiple covalent bond? a. chlorine c. fluorine b. hydrogen d. nitrogen 2. The chemical bonding in sodium phosphate, Na3PO4 is classified as a. ionic, only c. both covalent and ionic b. metallic, only d. both covalent and metallic 3. What is formed with two atoms of bromine bond together? a. a monoatomic molecule c. a homogeneous mixture b. a diatomic molecule d. a heterogeneous mixture 4. What is the total number of electron pairs shared between the two atoms in an O2 molecule? a. 1 c. 6 b. 2 d What is the total number of electrons shared in a double covalent bond formed between two atoms? a. 1 c. 8 b. 2 d Determine the number of bonds and lone pairs on the central atom (C) in CF4. a. 4 bonds and no lone pairs c. 3 bonds and 2 lone pairs b. 3 bonds and no lone pairs d. 3 bonds and 1 lone pair 7. Determine the number of bonds and lone pairs on the central atom (S) in SH2. a. 4 bonds and no lone pairs c. 2 bonds and 2 lone pairs b. 2 bonds and no lone pairs d. 2 bonds and 1 lone pair 8. Determine the number of bonds and lone pairs on the F in HF. a. 4 bonds and no lone pairs c. 1 bond and 2 lone pairs b. 2 bonds and 3 lone pairs d. 1 bonds and 3 lone pairs 9. How many pairs of electrons are shared by the central atom (C) in CS2? a. 1 c. 4 b. 2 d Determine the number of bonds and lone pairs on each S in CS2. a. 4 bonds and no lone pairs c. 2 bonds and 2 lone pairs b. 1 bond and 3 lone pairs d. 2 bonds and 3 lone pairs 7 th grade POST Pre-Comp Review 8

9 Chemical Names and Formulas: Modern Chemistry Ch. 7 Sec. 1 (pp ). Naming Compounds Binary I Binary II Binary III Ionic Ionic Covalent Formed between metal in group 1A, 2A, or Ag, Zn, Cd, Al, Ga, or In and a nonmetal (single ion or polyatomic ion) *the charge on the metal ion is always known* BaCl2 = barium chloride Sr(OH)2 = strontium hydroxide Formed between any metal that is NOT Binary I and a nonmetal (single ion or polyatomic ion) *the charge on the metal ion is NOT known it must be determined by analyzing the chemical formula* NiBr2 = nickel (II) bromide Mn(OH)4 = manganese (IV) hydroxide Formed between two nonmetals or metalloid and a nonmetal. *the number of covalent bonds each atom will made is easily determined by following the octet rule* P5O2 = pentaphosphorus dioxide GeS2 = germanium disulfide How do you figure out the charge on the metal ion for Binary II compounds? positive and negative charges must balance one another (number of metal ions) (charge of metal ion) + (number of nonmetal ions) (charge of nonmetal ion) = 0 known from chemical formula *UNKNOWN* known from chemical formula known from Periodic table Binary II Naming Practice: Equation: Name: 1. AuCl3 2. AgBr 3. V3N5 4. PbS2 5. Hg3(PO4)2 7 th grade POST Pre-Comp Review 9

10 General Naming Practice: Indicate whether the following compounds are Binary I, II, or III. Then, name them appropriately. 1. SnO2 Binary I II III. 2. AgNO3 Binary I II III. 3. Al2(SO4)3 Binary I II III. 4. TeCl4 Binary I II III. 5. Pb3P4 Binary I II III. 6. ScSO4 Binary I II III. 7. BrCl3 Binary I II III. 8. B3Si Binary I II III. 9. LiBr Binary I II III. 10. CdO Binary I II III. 7 th grade POST Pre-Comp Review 10