Praxis II Chemistry prep Karen M. Morris Univ. of Notre Dame

The Atom C 6 Carbon C 12 6 C 13 6 C 14 6 What we observe vs. What we represent

Let’s Practice 1.Explain why atomic weights of elements often differ markedly from whole numbers. 2. Determine the number of protons, electrons and neutrons in each: U Ni Ne 3.In what way do the isotopes of a given element differ? 1.Explain why one of the following is not a property of an element: a. boiling point b. density c. volume

The Periodic Table What we observe vs. What we represent DsRgCnUutUuqUupUuhUuo

Let’s Practice 1.Compare the atomic size of row 4 elements to row 5 elements. Describe the general trend as one goes from left to right across the periodic table. 1.Arrange the following ions in order of increasing size: Mg 2+, Na +, Al 3+ 1.In the following pairs of ions, identify which is most likely to exist and explain why you think so. Ca 2+ or Ca 2- S 2+ or S 2- 4.Why is the radius of a positive ion smaller than the radius of its parent atom?

Chemical Formulae and Equations Forming Chemical Compounds Ionic Covalent Writing Chemical Equations Law of Conservation of Matter What we observe vs. What we represent

Let’s Practice 1. The chemical formula of the compound dopamine is C 8 H 11 O 2 N Would you expect this to be an ionic or covalent compound? Explain… 1.Identify the pure compound as ionic or covalent: HClCuBr 2 F 2 Na 3 PO 4 CCl 4 AgCl

Let’s Practice 1.Balance the following chemical equations a. H 2 + Cl 2 HCl b. Na + H 2 O NaOH + H 2 c. Zn + AgCl ZnCl 2 + Ag d. KClO 3 KCl + O 2

Observations of Matter 1.Representations can be atoms or large quantities of atoms 2.Experimentally discovered that all large quantities represented by one number (discovered by Avogadro) and measured as x atoms 3.This is DEFINED as “1 mole” of matter 4.You measure this mass quantity in grams per mole. 1 mole of C contains X atoms and masses g 1 mole of H contains X atoms and masses g 1 mole of U contains X atoms and masses g

Compounds 1 mole of carbon dioxide, CO 2, contains x molecules of CO 2 and masses the sum of 1 Carbon plus 2 Oxygen: ( g) + 2(15.99 g) = g 1 mole of calcium carbonate, CaCO 3, contains _________ molecules of CaCO 3 and masses the sum of __________ A.K.A. as a “molar mass” (mass of 1 mole)

Compounds We can manipulate the molar mass of CO 2 to determine the mass percent of each element in the sample. This idea is the basis of quantitative analysis of materials. Molar Mass CO 2 = ( g) + 2(15.99 g) = g Mass % of C in the sample = [(12.011)/(43.99)] * 100 = 27.3% Mass % of O in the sample = [2(15.99)/(43.99)]* 100 = 72.7% or 100% % = 72.7% (the easy way ;-)

Let’s Practice H2OH2O H 2 + O 2 1.Something is “wrong” with this equation. Fix it. 2.After fixing it, determine the mass of each compound. 3.How many moles of hydrogen and oxygen do we get if we break down 3 moles of water? 4.How many grams of hydrogen to we get if we break down 3 moles of water? 5.What is the mass percent of hydrogen in water?

Let’s Practice What is the mass percent of carbon, C, in dopamine? The chemical formula of the compound dopamine is C 8 H 11 O 2 N What is the mass of 0.15 moles of dopamine? What is the molar mass of dopamine? How many moles of C are in 0.15 moles of dopamine? How many grams of C are in 0.15 moles of dopamine?

Let’s Practice a)H 2 + Cl 2 2 HCl a) Na + 2 H 2 O 2 NaOH + H 2 a)Zn + 2 AgCl ZnCl Ag a)2 KClO 3 2 KCl + 3 O 2

Physical Properties of Matter What we OBSERVE vs. what we REPRESENT 1.Ice cube melting 2.Melted puddle of water evaporating Phases of matter 1.Solid 2.Liquid 3.Gas

Let’s Practice 1.Draw representations of solid, liquid and gas at the atomic level. How are your drawings different? How the same? 1.What happens to a gas volume when it is compressed? What happens to a liquid volume when it is compressed? What happens to a solid volume when it is compressed? 1.What happens to a gas volume when it is heated? What happens to a liquid volume when it is heated? What happens to a solid volume when it is heated?

Chemical Changes What we OBSERVE vs. what we REPRESENT 1.Observed: a. Sometimes NOTHING!! Need instrumentation to measure b. Sometimes solid is formed, bubbles (gas), heat, light c. Reactant materials will not easily return. 2.Represented: a. Physical rearrangement of atoms b. Balance in number of atoms in reactants and products.

Let’s Practice a)H 2 (g) + Cl 2 (g) 2 HCl (g) a) Na (s) + 2 H 2 O (l) 2 NaOH (aq) + H 2 (g) a)Zn (s) + 2 AgCl (aq) ZnCl 2 (aq) + 2 Ag (s) a)2 KClO 3 (s) 2 KCl (s) + 3 O 2 (g)

General Types of Reactions Reaction Types: What we OBSERVE vs. what we REPRESENT Precipitation: MgCl NaOHMg(OH) NaCl 2 clear and colorless solutions poured together and a white solid appears Acid-Base Neutralization: HCl + NaOHH 2 O + NaCl a very acidic and a very basic solution poured together to form a clear and colorless neutral solution (salt + water)