CHEM 120: Introduction to Inorganic Chemistry. Chapters Covered and Test dates. The mole concept and atoms. Avogadro s number

Size: px

Start display at page:

Download "CHEM 120: Introduction to Inorganic Chemistry. Chapters Covered and Test dates. The mole concept and atoms. Avogadro s number"

Roxanne Anthony
5 years ago
Views:

1 CHEM 120: Introduction to Inorganic Chemistry Instructor: Upali Siriwardane (Ph.D., Ohio State University) CTH 311, Tele: , Office hours: 10:00 to 12:00 Tu & Th ; 8:00-9:00 and 11:00-12:00 M,W,& F Chapters Covered and Test dates Tests will be given in regular class periods from 9:30-10:45 a.m. on the following days: September 22, 2004 (Test 1): Chapters 1 & 2 October 8, 2004(Test 2): Chapters 3, & 4 October 20, 2004 (Test 3): Chapter 5 & 6 November 3, 2004 (Test 4): Chapter 7 & 8 November 15, 2004 (Test 5): Chapter 9 & 10 November 17, 2004 MAKE-UP: Comprehensive test (Covers all chapters Grading: [( Test 1 + Test 2 + Test3 + Test4 + Test5)] x.70 + [ Homework + quiz average] x 0.30 = Final Average 5 Chapter 5. Calculations and the Chemical Equation 5.1 The Mole Concept and Atoms The Mole and Avogadro's Number Calculating Atoms, Moles, and Mass 5.2 Compounds The Chemical Formula 5.3 The Mole Concept Applied to Compounds 5.4 The Chemical Equation and The Information It Conveys A Recipe for Chemical Change Features of a Chemical Equation The Experimental Basis of a Chemical Equation 5.5 Balancing Chemical Equations 5.6 Calculations Using the Chemical Equation General Principles Use of Conversion Factors Theoretical and Percent Yield Pharmaceutical Chemistry: The Practical Significance of Percent Yiel The mole concept and atoms In ch 1 we learned that 1 amu = x g So if the average mass of a gold atom is amu x x g = 3.27 x g 1 amu a very small no. Where did I get the anu for the mass of one Au atom? From the!!! If I write amu after these nos. it implies that I have the mass of atom of that element (in amu). But 3.27 x g is too small an amt to work with in the lab. What to do? Scale up to quantities that we can handle by Avogadro s number Defining one mole (mol) as amt of substance that contains as many elementary entities (atoms, molecules, ions, etc) as there are in atoms in exactly 12 g of the carbon-12 isotope. This is determined experimentally and is...

2 Useful relationship # moles X = #g X/molar mass X Some problems How many atoms are there in 5.10 moles of sulfur? What s the mass of 5.10 moles of S? How many moles of calcium atoms are in 1.16 x atoms of Ca? How many grams? Which of the following has more atoms: 1.10g of hydrogen atoms or 14.7 g of chromium atoms? How many moles are in kg Na? Compounds What s the mass, in grams, of one atom of potassium? One atom of some element has a mass of 1,45 x g. Identify the element. The chemical formula: MgO (ion pair) H 2 O C 12 H 22 O 11 Ca 3 (PO 4 ) 2 CuSO 4. 5H 2 O vs CuSO 4

3 The mole concept applied to compounds The formula weight of a species is the sum of atomic masses (amu) of the atoms in a species. Formula weight of NH 3 For an ionic compound MgF 2 = Covalent Cpds Molecular weight moles (Molar Mass) Ionic Cpds Formula weight Formula units (Molar Mass) In general we talk about molesfor covalent compounds formula units rather than moles of ionic compounds. Molar mass Mass of one mole of NH 3 : Mass of x molecules of NH 3 is Mass of one molecule of NH 3 is. Mass of one mole of MgF 2 is Mass of one formula unit of MgF 2 is Mass of x formula units of MgF 2 is Calc the molar mass of Ca(NO 3 ) 2. Calc the molar mass of a compound if mol of it has a mass of 152g How many grams of each are required to have mol of A. NaOH B. H 2 SO 4 C. C 2 H 5 OH D. Ca 3 (PO4) 2

4 5.40. How many moles are in 50.0 g of A. CS 2 Calc the no. of C, H, and O atoms in 1.50 g of glucose (C 6 H 12 O 6 ). B. Al 2 (CO 3 ) 3 What is the average mass of one C 3 H 8 molecule? C. Sr(OH) 2 D. LiNO 3 What is the mass of 5.00 x molecules of NH 3? Law of conservation of mass Mass is neither created nor destroyed in an ordinary chemical rxn. Or the sum of the masses of the reactants is equal to the sum of the masses of the products mercury + oxygen ---> mercury(ii)oxide 10.03g? 10.83g Easier to use symbols for chem eqns. reactants products lhs rhs may indicate physical state by (s), (g), (l), (aq)-aqueous solution Remember that H 2,N 2,O 2,F 2,Cl 2,Br 2,I 2 occur as diatomics in nature and are used as diatomics in chemical eqns To balance: Have to have same no of each kind of atom on both sides of the eqn. The bonding arrangement changes, but the no of each kind of atom doesn t change.

5 Reactants (reagents) a A + b B Conditions Products c C + d D Chemical equations Indicate phases of reactants and products Fe(s) + 2 HBr(aq) H 2 O FeBr 2 (aq) + H 2 (g) Coefficent Arrow indicates reaction. Conditions can include: Heat (specify temperature) ( ) Solvent Other information (s) = solid (l) = liquid (aq) = aqueous, dissolved in water Conditions etc. (g) = gas Balancing chemical eqns Use correct formulas for the reactants and products (if word eqn at start) Balance by putting coefficients (nos) in front of the formulas. You may not change the formulas! These coefficients are called the stoichiometric (measure of mass) coefficients. By convention use the lowest set of whole no. coefficients to balance. Start by balancing elements that appear only once on each side of the equation Balance remaining elements Check your balanced equation! To predict products--do an experiment To balance hydrogen + nitrogen ammonia 1. write the symbols for the species in the rxn Now figure out how to get the same no of atoms of each kind on both sides by using whole no coefficients in front of the species. As H 2 + _N 2 NH 3, then H 2 + _N 2 _ NH 3, then _ H 2 + _N 2 _ NH 3 Now have _ H s, _N s on both sides and the lowest set of whole no coefficients have been used. The equation is balanced.

6 3H 2 + N 2 2NH 3 3 mol of H 2 reacts with 1 mol of N 2 to form 2 mol of NH 3 3 molecules of H 2 reacts with 1 molecule of N 2 to form 2 molecules of NH 3 6H + 2N reacts to give 6H and 2N 6g of H 2 reacts with 28 g of N 2 to form 34g of NH 3 Note that Balance C 2 H 6 + O 2 CO 2 + H 2 O H 2 O 2 H 2 O + O 2 C 2 H 5 OH + O 2 CO 2 + H 2 O KOH + H 3 PO 4 K 3 PO 4 + H 2 O N 2 O 5 N 2 O 4 + O 2 Balance NH 4 NO 3 N 2 O + H 2 O Balance S 2 Cl 2 (s) + NH 3 (g) N 4 S 4 (s) + NH 4 Cl(s) + S 8 (s) NH 4 NO 2 N 2 + H 2 O Be 2 C + H 2 O Be(OH) 2 + CH 4 NH 3 + CuO Cu + N 2 + H 2 O Calculations using the chemical eqn Quantitative study of reactants and products in a chemical reaction How much product will be formed? How much reactant is needed? Use coefficients in a balanced equation to convert between moles of different substances in a chemical reaction. 3H 2 (g) + Chemical Reaction N 2 (g) > 2NH 3 (g) 3 mol H 2 (reactant) = 1 mol N 2 (reactant) consumed 3 mol H 2 (reactant) = 2 mol NH 3 (products) produced 1 mol N 2 (reactant) = 2 mol NH 3 (products) produced 3 x 2 (6) g H 2 (reactant) = 1x 28 (28)mol N 2 (reactant) consumed 3 x 2 H 2 (6) (reactant) = 2x 17 (34) NH 3 (products) produced 1 x 28 (28) g N 2 (reactant) = 2 x 17 (34) NH 3 (products) produced

7 Chemical reactions Hydrogen reacts with nitrogen to form NH 3. theoretically it is should be that when 6 g of hydrogen reacts completely with 28 g of nitrogen, 34 g of ammonia is formed. However in real chemical reactions actual g of hydrogen reacting with g of nitrogen, g of ammonia is produced need be experimentally determined. 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O How many moles of H 2 is needed to completely react with19.8 mol O 2? How many moles of H 2 O are formed when 25.4 mol of H 2 react? 2H 2 + O 2 2H 2 O How many moles of H 2 react with 38 g of O 2? What mass of H 2 O is formed when 59.0g of H 2 reacts completely with O 2? How much O 2 reacted in this case? Mass relationships in chemical equations Mole-to-mole conversions use mole ratios as conversion factors Mass-to-mole and mole-to-mass conversions use molecular weights as conversion factors Mass-to-mass conversions do in multiple steps General prescription

8 Problems How many grams of Al 2 O 3 can be produced from 15.0 g Al? 4 Al(s) + 3O 2 (g) 2Al 2 O 3 (s) C 3 H 8 + O 2 CO 2 + H 2 O balance How many mol of O 2 does it take to completely burn 7.0 mol of C 3 H 8? How many mol each of CO 2 and H 2 O are produced? How many grams of oxygen does it take to completely burn 25.0 g of C 3 H 8? How many grams each of CO 2 and H 2 O are produced when 25.0 g of C 3 H 8 is burned? Theoretical and percent yield A 4.00 g sample of Fe 3 O 4 reacts with O 2 to produce Fe 2 O 3. 4Fe 3 O 4 (s) + O 2 (g) 6Fe 2 O 3 (s) Determine the no. of grams of Fe 2 O 3 produced. How good an experimentalist are you? What if 100% of reactants are not converted to desired products? Frequently happens because of side reactions (other products), handling, etc. 100% amount is theoretical yield Amount obtained is actual yield Theoretical yield - amount of product that would result if all limiting reagent gave only product Actual yield - the amount of product actually obtained from a reaction (almost always less than the theoretical yield) Percent yield - calculated by % yield = actual yield 100% theoretical yield Theoretical yield is what we calculate assuming 100% conversion of reactants to products. In the combustion of 33.5g of C 3 H 6, 16.1 g of H 2 O is isolated. What is the percent yield?

9 If the % yield of Fe 2 O 3 in problem was 90.0% what was the actual yield of Fe 2 O 3? A 3.5 g sample of water reacts with PCl 3 according to : 3H 2 O + PCl 3 H 3 PO 3 + 3HCl. How many grams of H 3 PO 3 are produced?

Chapter 3. Mass Relationships in Chemical Reactions

Chapter 3. Mass Relationships in Chemical Reactions Chapter 3 Mass Relationships in Chemical Reactions In this chapter, Chemical structure and formulas in studying the mass relationships of atoms and molecules. To explain the composition of compounds and