# Concept 1. The meaning and usefulness of the mole. The mole (or mol) represents a certain number of objects.

Size: px
Start display at page:

Download "Concept 1. The meaning and usefulness of the mole. The mole (or mol) represents a certain number of objects."

Transcription

1 Chapter 3. Stoichiometry: Mole-Mass Relationships in Chemical Reactions Concept 1. The meaning and usefulness of the mole The mole (or mol) represents a certain number of objects. SI def.: the amount of a substance that contains the same number of entities as there are atoms in 12 g of carbon-12. Exactly 12 g of carbon-12 contains x atoms. 1 mole contains x entities (Avogadro s number) One mole of H 2O molecules contains x molecules. 1

2 One mole of NaCl contains x NaCl formula units. Use the mole quantity to count formulas by weighing them. Mass of a mole of particles = mass of 1 particle x x Mass of 1 H atom: amu x x10-24 g/amu = x10-24 g Mass of 1 mole of H atoms: x10-24 g/h atom x x10 23 H atoms = g The mass of an atom in amu is numerically the same as the mass of one mole of atoms of the element in grams. One atom of sulfur has a mass of amu; one mole of S atoms has a mass of g. PT 2

3 Concept 2. The relation between molecular (formula) mass and molar mass For compounds, the molecular mass (in amu) is numerically the same as the mass of one mole of the compound in grams. Skill 3-1 Calculate the molecular mass of a compound as the sum of the atomic masses of its elements. Molecular mass H 2 O = (2 x atomic mass of H) + atomic mass of O = 2(1.008 amu) amu = amu So, one mole of water (6.022 x molecules) has a mass of g. Molar mass of NaCl = atomic mass of Na (22.99 amu) + the atomic mass of Cl (35.45 amu) = amu One mol of NaCl (6.02 x10 23 formulas) has a mass of g. 3

4 To obtain one mole of copper atoms (6.02 x atoms), weigh out g copper. PT 4

5 Concept 3. The relations among amount of substance (in moles), mass (in grams), and number of chemical entities The molar mass (M) of a substance is the mass of one mole of entities (atoms, molecules, or formula units) of the substance. Molar mass has units of grams per mole (g/mol). 5

6 Skill 3-2 Mass - Mole Conversions Use the molar mass of an element or compound to convert a given number of moles to mass: We can do the reverse with 1/M, and convert any mass in grams to the number of moles: Use Avogadro s number to convert moles of substance to the number of entities: 6

7 Problem: (a) How many grams of silver, Ag, are in mol Ag? (b) How many atoms of Ag are in mol Ag? Plan: (a) To convert moles Ag to grams Ag, use the molar mass of Ag from the periodic table. (b) To convert moles to number of atoms, use Avogadro s number. Solution: (a) Converting from moles of Ag to mass: (b) Converting from moles of Ag to number of atoms: = 2.06 x atoms Ag PT 7

8 Problem: Iron is a most important metal in our society. How many iron atoms are present in a piece of iron weighing 95.8 g? Plan: Solution: Converting from mass of Fe to moles: Converting from moles of Fe to number of atoms: PT 8

9 Concept 4. The information in a chemical formula The sulfur dioxide formula, SO 2, shows that its molecules contain one S atom and two O atoms; calculate its molar mass. One mole SO 2 contains 6.02 x SO 2 molecules, which consist of 6.02 x S atoms and 2(6.02 x ) O atoms. Same for ionic compounds, such as potassium sulfide (K 2 S): 9

10 10

11 Problem: How many moles and formulas are in 41.6 g ammonium carbonate? Solution: Calculating molar mass: 11

12 Skill 3-3 Mass Percent and the Chemical Formula The formula shows the number of moles of each element; use it to calculate the mass percent of each element on a mole basis: % Problem: The formula of the sugar glucose is C 6 H 12 O 6. (a) What is the mass percent of each element in glucose? (b) How many grams of carbon are in g glucose? Plan: The formula gives the no. of moles of C, H and O in glucose. Convert from moles of element to grams using the molar mass. 12

13 Dividing by the mass of one mole of glucose gives the element s mass fraction; multiplying this fraction by 100% gives the mass percent. 13

14 (b) Determining the mass of carbon. Plan: To find the mass of C in the glucose sample, multiply the mass of the sample by the mass fraction of C from part (a) Solution: 14

15 Concept 5. The procedure for finding the empirical and molecular formulas of a compound If an unknown pure compound can be decomposed, the masses of elements present can be determined. Converting the masses to moles of elements leads to the empirical formula, the simplest whole-number ratio of moles of each element in the compound. Suppose a sample of unknown compound is found to contain 0.21 mol zinc, 0.14 mol phosphorus, and 0.56 mol oxygen. 15

16 A preliminary formula based on the data is Zn 0.21P 0.14O Convert the fractional subscripts to whole numbers. : 1. Divide each subscript by the smallest subscript: 2. If any subscripts are still not integers, multiply through by the smallest integer that will turn all the subscripts into integers. The conventional way to write this formula is Zn 3 (PO 4 ) 2 ; the compound is zinc phosphate, a dental cement. 16

17 Skill 3-4: Analysis of a sample of ionic compound gave: 2.82 g Na, 4.35 g Cl, and 7.83 g O. What is the empirical formula and name of the compound? Plan: Solution: Find moles of elements: From the moles of each element, construct a preliminary formula and convert to integer subscripts. PT 17

18 Preliminary formula: Convert to integer subscripts: Note that we rounded the subscript of O from 3.98 to 4. The empirical formula is NaClO 4 ; the name is sodium perchlorate. 18

19 Molecular Formulas The actual number of moles of each element in the smallest unit of the compound. In water (H 2 O), ammonia (NH 3 ), methane (CH 4 ), and ionic compounds, the empirical and molecular formulas are identical. In some cases the molecular formula is a whole-number multiple of the empirical formula. Using the empirical formula to obtain the molecular formula. Hydrogen peroxide has the empirical formula HO (17.01g/mol) Dividing its molar mass (34.02 g/mol) by the empirical formula mass gives the whole-number multiple: The molecular formula is H 2 O 2. 19

20 Skill 3-5 : Lactic acid (M = g/mol) contains 40.0 mass % C, 6.71 mass % H, and 53.3 mass % O. (a) Determine the empirical formula of lactic acid. (b) Determine the molecular formula. Plan: Assume 100 g lactic acid to express each mass % as grams. Convert grams to moles and find the empirical formula. Solution: Express mass % as grams; assume 100 g lactic acid: Similarly, there are 6.71 g H and 53.3 g O. Converting from grams of elements to moles: 20

21 Similarly, we have 6.66 mol H and 3.33 mol O. Constructing the preliminary formula: Converting to integer subscripts: Determining the molecular formula: Plan: Divide the molar mass by the empirical formula mass. Solution: Calculate the molecular formula: 21

22 Combustion Analysis Combustion analysis gives the amounts of carbon and hydrogen in a sample of combustible compound. The C forms CO 2, which is absorbed in the first chamber. The H forms H 2O, which is absorbed in the second chamber. Weigh the chambers before and after combustion. Calculate the masses of CO 2 and H 2O Use them to calculate the masses of C and H in the compound. From the masses, calculate the empirical formula. 22

23 Skill 3-5 contd: Vitamin C (M= 176. g/mol) contains C, H and O. A g sample was placed in a combustion apparatus: What is the molecular formula of vitamin C? Plan: -Use changes in mass of CO 2 and H 2O absorbers to calculate the moles of C and H present in the sample. -Find the mass of C, using the mass fraction of C in CO 2. Likewise, find the mass of H from the mass of H 2 O. -The mass of vitamin C minus the sum of the C and H masses gives the mass of O. -Construct the empirical formula and molecular formula. 23

24 Solution: Finding the masses of combustion products: Calculating mass fractions of the elements: 24

25 Calculate masses of C and H: Calculate mass of O by difference: Find the moles of elements: Divide mass of each by its molar mass gives mol C, mol H, and mol O. Construct the preliminary formula: 25

26 Divide through by the smallest subscript: Determine the empirical formula. By inspection, find that 3 is the smallest multiple that makes all subscripts into integers: Determine the molecular formula: 26

27 Chemical Formulas and the Structures of Molecules Chemical formulas represent real three-dimensional objects. The molecular formula tells the number of each type of atom. Molecular formulas may not be unique; the same types and numbers of atoms can bond to each other in more than one way Can be different compounds or structural isomers of the same compound (same molecular formulas). 27

28 Structural Formulas Consider C 2 H 6O; two very different compounds have this molecular formula: -ethanol, the intoxicating substance present in wine and beer -dimethyl ether, a colorless gas once used in refrigeration Their radically different physical and chemical behaviors are the result of different molecular structures. ethanol dimethyl ether 28

29 Concept 6. The importance of balancing equations for the quantitative study of chemical reactions For an equation to depict accurately the amounts of chemicals involved in a reaction, it must be balanced. The same number of each type of atom must appear on both sides of the equation. In a flashbulb Mg wire and oxygen gas react to yield magnesium oxide powder. 29

30 Translate the chemical statement into a skeleton equation: chemical formulas arranged in an equation format. reactants yield products Balancing the atoms Each blank must contain a balancing coefficient, a numerical multiplier of all the atoms in the formula that follows it. Stepwise, match the atoms on each side, element by element, beginning with the most complex substance. 31

31 Requires one Mg on the left. And one oxygen on the left. Adjusting the coefficients. The smallest whole-number coefficients are required. To remove the 1/2 O 2, multiply the whole equation by 2: A coefficient of 1 is implied by the presence of the substance and is not written: Check the numbers of atoms: Reaction equation is balanced. 32

32 Specifying the states of matter. A complete equation shows the physical state of each substance or whether it is dissolved in water. solid (s) liquid (l) gas (g) aqueous solution (aq) From the statement, Mg wire is solid, O 2 is a gas, and powdery MgO is a solid: 2Mg(s) + O 2 (g) 2MgO(s) 33

33 Skill 3-6: Octane (C 8 H 18 ) burns to form carbon dioxide and water vapor. Write a balanced equation for this reaction. Solution: Translate the statement into a skeleton equation (with coefficient blanks). Octane and oxygen are reactants; oxygen is molecular O 2. Carbon dioxide and water vapor are products: Balance the atoms. Start with the more complex reactant, C 8 H 18, then balance O 2 : 8 C on left requires 8 CO 2 on right: 34

34 18 H on left requires 9 H 2 O. 25 O on right requires 25/2 O 2 Adjust coefficients. Check that the equation is balanced: reactants (16 C, 36 H, 50 O) = products (16 C, 36 H, 50 O) States of matter: C 8H 18 is liquid; O 2, CO 2, and H 2O vapor are gases: 35

35 Concept 7 The mole-mass-number information contained in a balanced equation A balanced equation relates quantities of atoms, molecules, formula units, moles of substance, and masses. 36

36 Concept 8 The relation between amounts of reactants and products Quantitative relationships in a balanced equation are expressed as stoichiometrically equivalent molar ratios. Use stoichiometrically equivalent molar ratios to determine how much of one substance forms from (or reacts with) another. 3 mol CO 2 is stoichiometrically equivalent to 4 mol H 2 O, 5 mol O 2 is stoichiometrically equivalent to 3 mol CO 2, and so on. In the combustion of propane, how many moles of O 2 are consumed when 10.0 mol H 2O are produced? starting amt. molar ratio equiv. amt. 37

37 Skill 3-7: Copper is obtained from sulfide ores by roasting the ore with O 2 to form powdered copper(i) oxide and gaseous sulfur dioxide. (a) How many moles of oxygen are required to roast 10.0 mol copper(i) sulfide? Write the balanced equation first. The reactants are Cu 2 S and O 2, and the products are Cu 2 O and SO 2 : Given the moles of Cu 2 S; need to find the moles of O 2. (b) How many grams of sulfur dioxide are formed when 10.0 mol copper(i) sulfide are roasted? 38

38 Find mass of SO 2 that forms from the given mol of reactant (Cu 2 S). (c) How many kg of oxygen are needed to form 2.86 kg Cu 2 O? Convert mass Cu 2 O to mol: Mol Cu 2 O to mol O 2 : Mol O 2 to mass O 2 : 39

39 Chemical Reactions That Occur in a Sequence A product of one reaction can become a reactant of the next (reaction sequence). If a substance forms in one reaction and is used up in the next, write an overall equation that eliminates the substance altogether. Skill 3-8: Roasting chalcocite is the 1st step in extracting copper. [equation 1] Next step: copper(i) oxide reacts with powdered carbon to yield copper metal and carbon monoxide gas: [equation 2] (a) Write a balanced overall equation for the two-step sequence. Add the equations together. Only Cu 2O appears as a product in one equation and a reactant in the other, so it is the common substance. 40

40 Two mol Cu 2 O forms in eqn. 1; but one mol Cu 2O reacts in eqn. 2. Double all the coefficients in eq. 2; the Cu 2O from eqn. 1 is used up. Check: Reactants (4Cu, 2S, 6O, 2C) = products (4Cu, 2S, 6O, 2C) (b) Determine the mass (kg) of copper formed per metric ton of SO 2 that is produced. Convert mass of SO 2 to moles, apply the molar ratio from the overall equation to find mol of Cu, and then convert mol to mass (kg) of Cu. 41

41 Convert from mass of SO 2 to moles of SO 2 : Convert from moles of SO 2 to moles of Cu: Convert from moles of Cu to mass of Cu: 42

42 Concept 9 Why one reactant limits the yield of product If amounts of two reactants are not in the stoichiometric ratio of a reaction, one will be in excess; the other is the limiting reactant. Problem: Rocket fuel, [hydrazine (N 2 H 4 ) and dinitrogen tetraoxide (N 2 O 4 )], reacts to form N 2 gas and water vapor. How many grams of nitrogen gas form from 1.00 x 10 2 g N 2 H 4 and 2.00 x 10 2 g N 2 O 4? Write the balanced equation: Convert mass of reactants to mol and find the mol of N 2 each forms. 43

43 - Whichever yields less N 2 is the limiting reactant. N 2 H 4 is the limiting reactant because less N 2 can form (4.68 mol) when all the N 2 H 4 reacts. - Convert the lower number of moles of N 2 to mass of N 2. 44

44 Concept 10. The causes of lower-than-expected yields and the distinction between theoretical and actual yields Ideally 100% of the limiting reactant becomes product. This is the theoretical yield, amount of product indicated by the stoichiometrically equivalent molar ratio in balanced equation. The theoretical yield is rarely obtained due to several factors. The amount of product actually obtained is the actual yield. The percent yield (% yield) is the actual yield expressed as a percent of the theoretical yield: 45

45 Problem: Silicon carbide (SiC) is made by heating sand (silicon dioxide) with carbon. Carbon monoxide is also formed. From kg sand, 51.4 kg SiC are formed. What is the percent yield of SiC? Plan: Given the actual yield of SiC, need its theoretical yield to be able to calculate its percent yield. Steps: -Write the balanced equation, convert mass of SiO 2 to mol, find the mol of SiC from the molar ratio, and convert mol of SiC to mass to obtain the theoretical yield and the percent yield. Balanced equation. Convert the mass of SiO 2 to moles: 46

46 Converting from moles of SiC to mass: Calculating the percent yield: 47

47 In multistep reaction sequences, the percent yield of each reaction step is multiplied over the whole sequence. A six-step sequence has a theoretical yield of 35.0 g of final product. If each step has a 90.0% yield, what would be over-all actual yield? PT

48 Concept 11. The meanings of concentration and molarity Solution Concentration and the Calculation of Molarity Most reactions occur in solution, so quantitative aspects of solution reactions are important in chemistry and other sciences. Need to know the concentration of reactants - the number of mol in a given volume - to calculate the volume of solution that contains a given number of mol. Solutions consist of a lesser amount the solute, dissolved in a larger amount of another substance, the solvent. Molarity (M) expresses solution concentration in terms of moles of solute per liter of solution: 48

49 Problem: Hydrochloric acid is a solution of HCl gas in water. Calculate the molarity of hydrochloric acid solution if 455 ml contains 1.80 mol hydrogen chloride. Plan: Solution: Molarity is a conversion factor that extends the stoichiometric relationships among substances. It can be used to convert between volume of solution and moles of solute. 49

50 50

51 Problem: How many grams of solute are in 1.75 L of M sodium monohydrogen phosphate? Plan: Solution: Calculating moles of solute in solution: Converting from moles of solute to mass: 51

52 Laboratory Preparation of Molar Solutions Volume term in molarity is solution volume, not solvent volume. Solution volume includes contributions from both solute and solvent. The solute and solvent volumes are not additive, so measure solution volume. To prepare L of M nickel(ii) nitrate hexahydrate, [Ni(NO 3 ) 2 6H 2 O]: 1. Weigh out 50.9 g of the solid. 52

53 2. Transfer the solid to a volumetric flask that contains about half the final amount of solvent. 3. Dissolve the solid completely by swirling the contents of the flask. 53

54 4. Add solvent until the solution reaches its final volume. 54

55 Concept 12. Effect of dilution on concentration of solute When sovent is added to a solution, it becomes more dilute (lower concentration). When lower concentrations of a solution are needed, use a more - concentrated stock solution which can be stored and diluted as needed. 55

56 Problem: Isotonic saline is 0.15 M NaCl(aq). How would you prepare L isotonic saline from a 6.0 M stock solution? Plan: Solution: Finding moles of solute in dilute solution: Since we add only solvent to dilute the solution, Mol of NaCl in diluted soln = mol of NaCl in concentrated sol n. = 0.12 mol NaCl 56

57 Finding the volume of stock solution that contains 0.12 mol NaCl: To prepare L dilute solution, place L of 6.0 M NaCl in a flask, add distilled water to the L mark, and stir thoroughly. An alternative approach to solving dilution problems makes use of the formula: 57

58 Concept 13. How reactions in solution differ from those of pure reactants. Stoichiometry problems in solution need the added step of converting solution volume to mol of reactant/product. Problem: Milk of Magnesia antacid reacts with acid to form water and magnesium chloride solution. How many liters of 0.1 M HCl react with a tablet containing 0.10 g magnesium hydroxide? Plan: Knowing the mass of Mg(OH) 2 that reacts with the acid and the acid concentration, and find the acid volume. Solution: Writing the balanced equation: Converting from mass of Mg(OH) 2 to moles: 58

59 Converting from moles of Mg(OH) 2 to moles of HCl: Converting from moles of HCl to volume: Solving Limiting-Reactant Problems for Reactions in Solution Problem: Toxic mercury compounds can be removed from solution by reaction with Na 2 S solution giving solid HgS. If L of M mercury(ii) nitrate reacts with L of 0.10 M sodium sulfide, how many grams of HgS can be formed? 59

60 Plan: Balance the equation, determine the limiting reactant and convert moles of HgS it produces to mass using the molar mass of HgS. Solution: Write the balanced equation: Finding moles of HgS assuming Hg(NO 3 ) 2 is limiting: Finding moles of HgS assuming Na 2S is limiting: 60

61 Larger than 5.0 x 10-4, therefore, Hg(NO 3 ) 2 is the limiting reactant. Converting from moles of HgS to mass: 61

62 PT

### Atomic mass is the mass of an atom in atomic mass units (amu)

Micro World atoms & molecules Laboratory scale measurements Atomic mass is the mass of an atom in atomic mass units (amu) By definition: 1 atom 12 C weighs 12 amu On this scale 1 H = 1.008 amu 16 O = 16.00

### Stoichiometry of Formulas and Equations

sil07204_ch03_69-107 8/22/05 15:16 Page 69 CHAPTER THREE Stoichiometry of Formulas and Equations Key Principles The mole (mol) is the standard unit for amount of substance and consists of Avogadro s number

### Formulas, Equations and Moles

Chapter 3 Formulas, Equations and Moles Interpreting Chemical Equations You can interpret a balanced chemical equation in many ways. On a microscopic level, two molecules of H 2 react with one molecule

### Moles. Balanced chemical equations Molar ratios Mass Composition Empirical and Molecular Mass Predicting Quantities Equations

Moles Balanced chemical equations Molar ratios Mass Composition Empirical and Molecular Mass Predicting Quantities Equations Micro World atoms & molecules Macro World grams Atomic mass is the mass of an

### Calculation of Molar Masses. Molar Mass. Solutions. Solutions

Molar Mass Molar mass = Mass in grams of one mole of any element, numerically equal to its atomic weight Molar mass of molecules can be determined from the chemical formula and molar masses of elements

### Chapter 3 Mass Relationships in Chemical Reactions

Chapter 3 Mass Relationships in Chemical Reactions Student: 1. An atom of bromine has a mass about four times greater than that of an atom of neon. Which choice makes the correct comparison of the relative

### Chapter 1: Moles and equations. Learning outcomes. you should be able to:

Chapter 1: Moles and equations 1 Learning outcomes you should be able to: define and use the terms: relative atomic mass, isotopic mass and formula mass based on the 12 C scale perform calculations, including

### Chemical Equations & Stoichiometry

Chemical Equations & Stoichiometry Chapter Goals Balance equations for simple chemical reactions. Perform stoichiometry calculations using balanced chemical equations. Understand the meaning of the term

### Calculating Atoms, Ions, or Molecules Using Moles

TEKS REVIEW 8B Calculating Atoms, Ions, or Molecules Using Moles TEKS 8B READINESS Use the mole concept to calculate the number of atoms, ions, or molecules in a sample TEKS_TXT of material. Vocabulary

### Part One: Mass and Moles of Substance. Molecular Mass = sum of the Atomic Masses in a molecule

CHAPTER THREE: CALCULATIONS WITH CHEMICAL FORMULAS AND EQUATIONS Part One: Mass and Moles of Substance A. Molecular Mass and Formula Mass. (Section 3.1) 1. Just as we can talk about mass of one atom of

### Study Guide For Chapter 7

Name: Class: Date: ID: A Study Guide For Chapter 7 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. The number of atoms in a mole of any pure substance

### IB Chemistry 1 Mole. One atom of C-12 has a mass of 12 amu. One mole of C-12 has a mass of 12 g. Grams we can use more easily.

The Mole Atomic mass units and atoms are not convenient units to work with. The concept of the mole was invented. This was the number of atoms of carbon-12 that were needed to make 12 g of carbon. 1 mole

### W1 WORKSHOP ON STOICHIOMETRY

INTRODUCTION W1 WORKSHOP ON STOICHIOMETRY These notes and exercises are designed to introduce you to the basic concepts required to understand a chemical formula or equation. Relative atomic masses of

### Chem 1100 Chapter Three Study Guide Answers Outline I. Molar Mass and Moles A. Calculations of Molar Masses

Chem 1100 Chapter Three Study Guide Answers Outline I. Molar Mass and Moles A. Calculations of Molar Masses B. Calculations of moles C. Calculations of number of atoms from moles/molar masses 1. Avagadro

### MOLES AND MOLE CALCULATIONS

35 MOLES ND MOLE CLCULTIONS INTRODUCTION The purpose of this section is to present some methods for calculating both how much of each reactant is used in a chemical reaction, and how much of each product

### IB Chemistry. DP Chemistry Review

DP Chemistry Review Topic 1: Quantitative chemistry 1.1 The mole concept and Avogadro s constant Assessment statement Apply the mole concept to substances. Determine the number of particles and the amount

### Other Stoich Calculations A. mole mass (mass mole) calculations. GIVEN mol A x CE mol B. PT g A CE mol A MOLE MASS :

Chem. I Notes Ch. 12, part 2 Using Moles NOTE: Vocabulary terms are in boldface and underlined. Supporting details are in italics. 1 MOLE = 6.02 x 10 23 representative particles (representative particles

### Chapter 3: Stoichiometry

Chapter 3: Stoichiometry Key Skills: Balance chemical equations Predict the products of simple combination, decomposition, and combustion reactions. Calculate formula weights Convert grams to moles and

### Unit 3 Notepack Chapter 7 Chemical Quantities Qualifier for Test

Unit 3 Notepack Chapter 7 Chemical Quantities Qualifier for Test NAME Section 7.1 The Mole: A Measurement of Matter A. What is a mole? 1. Chemistry is a quantitative science. What does this term mean?

### The Mole Concept. The Mole. Masses of molecules

The Mole Concept Ron Robertson r2 c:\files\courses\1110-20\2010 final slides for web\mole concept.docx The Mole The mole is a unit of measurement equal to 6.022 x 10 23 things (to 4 sf) just like there

### Chapter 1 The Atomic Nature of Matter

Chapter 1 The Atomic Nature of Matter 6. Substances that cannot be decomposed into two or more simpler substances by chemical means are called a. pure substances. b. compounds. c. molecules. d. elements.

### Unit 10A Stoichiometry Notes

Unit 10A Stoichiometry Notes Stoichiometry is a big word for a process that chemist s use to calculate amounts in reactions. It makes use of the coefficient ratio set up by balanced reaction equations

### Solution. Practice Exercise. Concept Exercise

Example Exercise 9.1 Atomic Mass and Avogadro s Number Refer to the atomic masses in the periodic table inside the front cover of this textbook. State the mass of Avogadro s number of atoms for each of

### Unit 9 Stoichiometry Notes (The Mole Continues)

Unit 9 Stoichiometry Notes (The Mole Continues) is a big word for a process that chemist s use to calculate amounts in reactions. It makes use of the coefficient ratio set up by balanced reaction equations

### Chapter 3. Chemical Reactions and Reaction Stoichiometry. Lecture Presentation. James F. Kirby Quinnipiac University Hamden, CT

Lecture Presentation Chapter 3 Chemical Reactions and Reaction James F. Kirby Quinnipiac University Hamden, CT The study of the mass relationships in chemistry Based on the Law of Conservation of Mass

### Formulae, stoichiometry and the mole concept

3 Formulae, stoichiometry and the mole concept Content 3.1 Symbols, Formulae and Chemical equations 3.2 Concept of Relative Mass 3.3 Mole Concept and Stoichiometry Learning Outcomes Candidates should be

### Sample Exercise 3.1 Interpreting and Balancing Chemical Equations

Sample Exercise 3.1 Interpreting and Balancing Chemical Equations The following diagram represents a chemical reaction in which the red spheres are oxygen atoms and the blue spheres are nitrogen atoms.

### Chapter 5, Calculations and the Chemical Equation

1. How many iron atoms are present in one mole of iron? Ans. 6.02 1023 atoms 2. How many grams of sulfur are found in 0.150 mol of sulfur? [Use atomic weight: S, 32.06 amu] Ans. 4.81 g 3. How many moles

### Chemical Calculations: Formula Masses, Moles, and Chemical Equations

Chemical Calculations: Formula Masses, Moles, and Chemical Equations Atomic Mass & Formula Mass Recall from Chapter Three that the average mass of an atom of a given element can be found on the periodic

### Lecture 5, The Mole. What is a mole?

Lecture 5, The Mole What is a mole? Moles Atomic mass unit and the mole amu definition: 12 C = 12 amu. The atomic mass unit is defined this way. 1 amu = 1.6605 x 10-24 g How many 12 C atoms weigh 12 g?

### SCH 4C1 Unit 2 Problem Set Questions taken from Frank Mustoe et all, "Chemistry 11", McGraw-Hill Ryerson, 2001

SCH 4C1 Unit 2 Problem Set Questions taken from Frank Mustoe et all, "Chemistry 11", McGraw-Hill Ryerson, 2001 1. A small pin contains 0.0178 mol of iron. How many atoms of iron are in the pin? 2. A sample

### Stoichiometry Review

Stoichiometry Review There are 20 problems in this review set. Answers, including problem set-up, can be found in the second half of this document. 1. N 2 (g) + 3H 2 (g) --------> 2NH 3 (g) a. nitrogen

### ATOMS. Multiple Choice Questions

Chapter 3 ATOMS AND MOLECULES Multiple Choice Questions 1. Which of the following correctly represents 360 g of water? (i) 2 moles of H 2 0 (ii) 20 moles of water (iii) 6.022 10 23 molecules of water (iv)

### Chapter 3 Stoichiometry

Chapter 3 Stoichiometry 3-1 Chapter 3 Stoichiometry In This Chapter As you have learned in previous chapters, much of chemistry involves using macroscopic measurements to deduce what happens between atoms

### Chapter 6 Chemical Calculations

Chapter 6 Chemical Calculations 1 Submicroscopic Macroscopic 2 Chapter Outline 1. Formula Masses (Ch 6.1) 2. Percent Composition (supplemental material) 3. The Mole & Avogadro s Number (Ch 6.2) 4. Molar

### Atomic Masses. Chapter 3. Stoichiometry. Chemical Stoichiometry. Mass and Moles of a Substance. Average Atomic Mass

Atomic Masses Chapter 3 Stoichiometry 1 atomic mass unit (amu) = 1/12 of the mass of a 12 C atom so one 12 C atom has a mass of 12 amu (exact number). From mass spectrometry: 13 C/ 12 C = 1.0836129 amu

### Problem Solving. Stoichiometry of Gases

Skills Worksheet Problem Solving Stoichiometry of Gases Now that you have worked with relationships among moles, mass, and volumes of gases, you can easily put these to work in stoichiometry calculations.

### Chem 31 Fall 2002. Chapter 3. Stoichiometry: Calculations with Chemical Formulas and Equations. Writing and Balancing Chemical Equations

Chem 31 Fall 2002 Chapter 3 Stoichiometry: Calculations with Chemical Formulas and Equations Writing and Balancing Chemical Equations 1. Write Equation in Words -you cannot write an equation unless you

### EXPERIMENT 12: Empirical Formula of a Compound

EXPERIMENT 12: Empirical Formula of a Compound INTRODUCTION Chemical formulas indicate the composition of compounds. A formula that gives only the simplest ratio of the relative number of atoms in a compound

### Balance the following equation: KClO 3 + C 12 H 22 O 11 KCl + CO 2 + H 2 O

Balance the following equation: KClO 3 + C 12 H 22 O 11 KCl + CO 2 + H 2 O Ans: 8 KClO 3 + C 12 H 22 O 11 8 KCl + 12 CO 2 + 11 H 2 O 3.2 Chemical Symbols at Different levels Chemical symbols represent

### Stoichiometry. Lecture Examples Answer Key

Stoichiometry Lecture Examples Answer Key Ex. 1 Balance the following chemical equations: 3 NaBr + 1 H 3 PO 4 3 HBr + 1 Na 3 PO 4 2 C 3 H 5 N 3 O 9 6 CO 2 + 3 N 2 + 5 H 2 O + 9 O 2 2 Ca(OH) 2 + 2 SO 2

### Chapter 4. Chemical Composition. Chapter 4 Topics H 2 S. 4.1 Mole Quantities. The Mole Scale. Molar Mass The Mass of 1 Mole

Chapter 4 Chemical Composition Chapter 4 Topics 1. Mole Quantities 2. Moles, Masses, and Particles 3. Determining Empirical Formulas 4. Chemical Composition of Solutions Copyright The McGraw-Hill Companies,

### 4.3 Reaction Stoichiometry

196 Chapter 4 Stoichiometry of Chemical Reactions 4.3 Reaction Stoichiometry By the end of this section, you will be able to: Explain the concept of stoichiometry as it pertains to chemical reactions Use

### Chapter Three: STOICHIOMETRY

p70 Chapter Three: STOICHIOMETRY Contents p76 Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions. p70 3-1 Counting by Weighing 3-2 Atomic Masses p78 Mass Mass

### Element of same atomic number, but different atomic mass o Example: Hydrogen

Atomic mass: p + = protons; e - = electrons; n 0 = neutrons p + + n 0 = atomic mass o For carbon-12, 6p + + 6n 0 = atomic mass of 12.0 o For chlorine-35, 17p + + 18n 0 = atomic mass of 35.0 atomic mass

### Mole Notes.notebook. October 29, 2014

1 2 How do chemists count atoms/formula units/molecules? How do we go from the atomic scale to the scale of everyday measurements (macroscopic scale)? The gateway is the mole! But before we get to the

### Unit 2: Quantities in Chemistry

Mass, Moles, & Molar Mass Relative quantities of isotopes in a natural occurring element (%) E.g. Carbon has 2 isotopes C-12 and C-13. Of Carbon s two isotopes, there is 98.9% C-12 and 11.1% C-13. Find

### Moles. Moles. Moles. Moles. Balancing Eqns. Balancing. Balancing Eqns. Symbols Yields or Produces. Like a recipe:

Like a recipe: Balancing Eqns Reactants Products 2H 2 (g) + O 2 (g) 2H 2 O(l) coefficients subscripts Balancing Eqns Balancing Symbols (s) (l) (aq) (g) or Yields or Produces solid liquid (pure liquid)

### Lecture Topics Atomic weight, Mole, Molecular Mass, Derivation of Formulas, Percent Composition

Mole Calculations Chemical Equations and Stoichiometry Lecture Topics Atomic weight, Mole, Molecular Mass, Derivation of Formulas, Percent Composition Chemical Equations and Problems Based on Miscellaneous

### Stoichiometry. What is the atomic mass for carbon? For zinc?

Stoichiometry Atomic Mass (atomic weight) Atoms are so small, it is difficult to discuss how much they weigh in grams We use atomic mass units an atomic mass unit (AMU) is one twelfth the mass of the catbon-12

### CHAPTER 3 Calculations with Chemical Formulas and Equations. atoms in a FORMULA UNIT

CHAPTER 3 Calculations with Chemical Formulas and Equations MOLECULAR WEIGHT (M. W.) Sum of the Atomic Weights of all atoms in a MOLECULE of a substance. FORMULA WEIGHT (F. W.) Sum of the atomic Weights

### How much does a single atom weigh? Different elements weigh different amounts related to what makes them unique.

How much does a single atom weigh? Different elements weigh different amounts related to what makes them unique. What units do we use to define the weight of an atom? amu units of atomic weight. (atomic

### Stoichiometry. Unit Outline

3 Stoichiometry Unit Outline 3.1 The Mole and Molar Mass 3.2 Stoichiometry and Compound Formulas 3.3 Stoichiometry and Chemical Reactions 3.4 Stoichiometry and Limiting Reactants 3.5 Chemical Analysis

### 1. What is the molecular formula of a compound with the empirical formula PO and a gram-molecular mass of 284 grams?

Name: Tuesday, May 20, 2008 1. What is the molecular formula of a compound with the empirical formula PO and a gram-molecular mass of 284 grams? 2 5 1. P2O 5 3. P10O4 2. P5O 2 4. P4O10 2. Which substance

### 1. When the following equation is balanced, the coefficient of Al is. Al (s) + H 2 O (l)? Al(OH) 3 (s) + H 2 (g)

1. When the following equation is balanced, the coefficient of Al is. Al (s) + H 2 O (l)? Al(OH) (s) + H 2 (g) A) 1 B) 2 C) 4 D) 5 E) Al (s) + H 2 O (l)? Al(OH) (s) + H 2 (g) Al (s) + H 2 O (l)? Al(OH)

### THE MOLE / COUNTING IN CHEMISTRY

1 THE MOLE / COUNTING IN CHEMISTRY ***A mole is 6.0 x 10 items.*** 1 mole = 6.0 x 10 items 1 mole = 60, 00, 000, 000, 000, 000, 000, 000 items Analogy #1 1 dozen = 1 items 18 eggs = 1.5 dz. - to convert

### 4.4 Calculations Involving the Mole Concept

44 Section 43 Questions 1 Define Avogadro s constant, and explain its significance in quantitative analysis 2 Distinguish between the terms atomic mass and molar mass 3 Calculate the mass of a molecule

### Chapter 3! Stoichiometry: Calculations with Chemical Formulas and Equations. Stoichiometry

Chapter 3! : Calculations with Chemical Formulas and Equations Anatomy of a Chemical Equation CH 4 (g) + 2O 2 (g) CO 2 (g) + 2 H 2 O (g) Anatomy of a Chemical Equation CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2

### Amount of Substance. http://www.avogadro.co.uk/definitions/elemcompmix.htm

Page 1 of 14 Amount of Substance Key terms in this chapter are: Element Compound Mixture Atom Molecule Ion Relative Atomic Mass Avogadro constant Mole Isotope Relative Isotopic Mass Relative Molecular

### Chemical Composition Review Mole Calculations Percent Composition. Copyright Cengage Learning. All rights reserved. 8 1

Chemical Composition Review Mole Calculations Percent Composition Copyright Cengage Learning. All rights reserved. 8 1 QUESTION Suppose you work in a hardware store and a customer wants to purchase 500

### Name Date Class STOICHIOMETRY. SECTION 12.1 THE ARITHMETIC OF EQUATIONS (pages 353 358)

Name Date Class 1 STOICHIOMETRY SECTION 1.1 THE ARITHMETIC OF EQUATIONS (pages 353 358) This section explains how to calculate the amount of reactants required or product formed in a nonchemical process.

### Ch. 10 The Mole I. Molar Conversions

Ch. 10 The Mole I. Molar Conversions I II III IV A. What is the Mole? A counting number (like a dozen) Avogadro s number (N A ) 1 mole = 6.022 10 23 representative particles B. Mole/Particle Conversions

### CHEMICAL REACTIONS. Chemistry 51 Chapter 6

CHEMICAL REACTIONS A chemical reaction is a rearrangement of atoms in which some of the original bonds are broken and new bonds are formed to give different chemical structures. In a chemical reaction,

### Calculations and Chemical Equations. Example: Hydrogen atomic weight = 1.008 amu Carbon atomic weight = 12.001 amu

Calculations and Chemical Equations Atomic mass: Mass of an atom of an element, expressed in atomic mass units Atomic mass unit (amu): 1.661 x 10-24 g Atomic weight: Average mass of all isotopes of a given

### CP Chemistry Review for Stoichiometry Test

CP Chemistry Review for Stoichiometry Test Stoichiometry Problems (one given reactant): 1. Make sure you have a balanced chemical equation 2. Convert to moles of the known substance. (Use the periodic

### 1. How many hydrogen atoms are in 1.00 g of hydrogen?

MOLES AND CALCULATIONS USING THE MOLE CONCEPT INTRODUCTORY TERMS A. What is an amu? 1.66 x 10-24 g B. We need a conversion to the macroscopic world. 1. How many hydrogen atoms are in 1.00 g of hydrogen?

### MOLECULAR MASS AND FORMULA MASS

1 MOLECULAR MASS AND FORMULA MASS Molecular mass = sum of the atomic weights of all atoms in the molecule. Formula mass = sum of the atomic weights of all atoms in the formula unit. 2 MOLECULAR MASS AND

### STOICHIOMETRY UNIT 1 LEARNING OUTCOMES. At the end of this unit students will be expected to:

STOICHIOMETRY LEARNING OUTCOMES At the end of this unit students will be expected to: UNIT 1 THE MOLE AND MOLAR MASS define molar mass and perform mole-mass inter-conversions for pure substances explain

### Unit 6 The Mole Concept

Chemistry Form 3 Page 62 Ms. R. Buttigieg Unit 6 The Mole Concept See Chemistry for You Chapter 28 pg. 352-363 See GCSE Chemistry Chapter 5 pg. 70-79 6.1 Relative atomic mass. The relative atomic mass

### Name Class Date. Section: Calculating Quantities in Reactions. Complete each statement below by writing the correct term or phrase.

Skills Worksheet Concept Review Section: Calculating Quantities in Reactions Complete each statement below by writing the correct term or phrase. 1. All stoichiometric calculations involving equations

### Ch. 6 Chemical Composition and Stoichiometry

Ch. 6 Chemical Composition and Stoichiometry The Mole Concept [6.2, 6.3] Conversions between g mol atoms [6.3, 6.4, 6.5] Mass Percent [6.6, 6.7] Empirical and Molecular Formula [6.8, 6.9] Bring your calculators!

### neutrons are present?

AP Chem Summer Assignment Worksheet #1 Atomic Structure 1. a) For the ion 39 K +, state how many electrons, how many protons, and how many 19 neutrons are present? b) Which of these particles has the smallest

### Calculations with Chemical Formulas and Equations

Chapter 3 Calculations with Chemical Formulas and Equations Concept Check 3.1 You have 1.5 moles of tricycles. a. How many moles of seats do you have? b. How many moles of tires do you have? c. How could

### CHEMICAL FORMULA COEFFICIENTS AND SUBSCRIPTS. Chapter 3: Molecular analysis 3O 2 2O 3

Chapter 3: Molecular analysis Read: BLB 3.3 3.5 H W : BLB 3:21a, c, e, f, 25, 29, 37,49, 51, 53 Supplemental 3:1 8 CHEMICAL FORMULA Formula that gives the TOTAL number of elements in a molecule or formula

### Chemistry Post-Enrolment Worksheet

Name: Chemistry Post-Enrolment Worksheet The purpose of this worksheet is to get you to recap some of the fundamental concepts that you studied at GCSE and introduce some of the concepts that will be part

### Chemistry B11 Chapter 4 Chemical reactions

Chemistry B11 Chapter 4 Chemical reactions Chemical reactions are classified into five groups: A + B AB Synthesis reactions (Combination) H + O H O AB A + B Decomposition reactions (Analysis) NaCl Na +Cl

### The Mole. Chapter 10. Dimensional Analysis. The Mole. How much mass is in one atom of carbon-12? Molar Mass of Atoms 3/1/2015

The Mole Chapter 10 1 Objectives Use the mole and molar mass to make conversions among moles, mass, and number of particles Determine the percent composition of the components of a compound Calculate empirical

### Chapter 6 Notes. Chemical Composition

Chapter 6 Notes Chemical Composition Section 6.1: Counting By Weighing We can weigh a large number of the objects and find the average mass. Once we know the average mass we can equate that to any number

### HOMEWORK 4A. Definitions. Oxidation-Reduction Reactions. Questions

HOMEWORK 4A Oxidation-Reduction Reactions 1. Indicate whether a reaction will occur or not in each of following. Wtiring a balcnced equation is not necessary. (a) Magnesium metal is added to hydrochloric

### Chemistry Final Study Guide

Name: Class: Date: Chemistry Final Study Guide Multiple Choice Identify the choice that best completes the statement or answers the question. 1. The electrons involved in the formation of a covalent bond

### Chemistry 65 Chapter 6 THE MOLE CONCEPT

THE MOLE CONCEPT Chemists find it more convenient to use mass relationships in the laboratory, while chemical reactions depend on the number of atoms present. In order to relate the mass and number of

### Name Date Class CHEMICAL QUANTITIES. SECTION 10.1 THE MOLE: A MEASUREMENT OF MATTER (pages 287 296)

10 CHEMICAL QUANTITIES SECTION 10.1 THE MOLE: A MEASUREMENT OF MATTER (pages 287 296) This section defines the mole and explains how the mole is used to measure matter. It also teaches you how to calculate

### Chemical Calculations: The Mole Concept and Chemical Formulas. AW Atomic weight (mass of the atom of an element) was determined by relative weights.

1 Introduction to Chemistry Atomic Weights (Definitions) Chemical Calculations: The Mole Concept and Chemical Formulas AW Atomic weight (mass of the atom of an element) was determined by relative weights.

### 11-1 Stoichiometry. Represents

11-1 Stoichiometry What is stoichiometry? Calculations that relate the quantities of substances. It is the study of quantitative (measurable amounts) relationships in chemical reactions and equations.

### CHEMICAL REACTIONS AND REACTING MASSES AND VOLUMES

CHEMICAL REACTIONS AND REACTING MASSES AND VOLUMES The meaning of stoichiometric coefficients: 2 H 2 (g) + O 2 (g) 2 H 2 O(l) number of reacting particles 2 molecules of hydrogen react with 1 molecule

### Chapter 8 How to Do Chemical Calculations

Chapter 8 How to Do Chemical Calculations Chemistry is both a qualitative and a quantitative science. In the laboratory, it is important to be able to measure quantities of chemical substances and, as

### Balancing chemical reaction equations (stoichiometry)

Balancing chemical reaction equations (stoichiometry) This worksheet and all related files are licensed under the Creative Commons Attribution License, version 1.0. To view a copy of this license, visit

### MASS RELATIONSHIPS IN CHEMICAL REACTIONS

MASS RELATIONSHIPS IN CHEMICAL REACTIONS 1. The mole, Avogadro s number and molar mass of an element. Molecular mass (molecular weight) 3. Percent composition of compounds 4. Empirical and Molecular formulas

### AS1 MOLES. oxygen molecules have the formula O 2 the relative mass will be 2 x 16 = 32 so the molar mass will be 32g mol -1

Moles 1 MOLES The mole the standard unit of amount of a substance the number of particles in a mole is known as Avogadro s constant (L) Avogadro s constant has a value of 6.023 x 10 23 mol -1. Example

### Aqueous Solutions. Water is the dissolving medium, or solvent. Some Properties of Water. A Solute. Types of Chemical Reactions.

Aqueous Solutions and Solution Stoichiometry Water is the dissolving medium, or solvent. Some Properties of Water Water is bent or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration

### Chemical Composition. Introductory Chemistry: A Foundation FOURTH EDITION. Atomic Masses. Atomic Masses. Atomic Masses. Chapter 8

Introductory Chemistry: A Foundation FOURTH EDITION by Steven S. Zumdahl University of Illinois Chemical Composition Chapter 8 1 2 Atomic Masses Balanced equation tells us the relative numbers of molecules

### The Mole. Chapter 2. Solutions for Practice Problems

Chapter 2 The Mole Note to teacher: You will notice that there are two different formats for the Sample Problems in the student textbook. Where appropriate, the Sample Problem contains the full set of

### F321 MOLES. Example If 1 atom has a mass of 1.241 x 10-23 g 1 mole of atoms will have a mass of 1.241 x 10-23 g x 6.02 x 10 23 = 7.

Moles 1 MOLES The mole the standard unit of amount of a substance (mol) the number of particles in a mole is known as Avogadro s constant (N A ) Avogadro s constant has a value of 6.02 x 10 23 mol -1.

### The Mole and Molar Mass

The Mole and Molar Mass 1 Molar mass is the mass of one mole of a substance. Molar mass is numerically equal to atomic mass, molecular mass, or formula mass. However the units of molar mass are g/mol.

### Appendix D. Reaction Stoichiometry D.1 INTRODUCTION

Appendix D Reaction Stoichiometry D.1 INTRODUCTION In Appendix A, the stoichiometry of elements and compounds was presented. There, the relationships among grams, moles and number of atoms and molecules

### Chem 115 POGIL Worksheet - Week 4 Moles & Stoichiometry

Chem 115 POGIL Worksheet - Week 4 Moles & Stoichiometry Why? Chemists are concerned with mass relationships in chemical reactions, usually run on a macroscopic scale (grams, kilograms, etc.). To deal with

### Problem Solving. Percentage Yield

Skills Worksheet Problem Solving Percentage Yield Although we can write perfectly balanced equations to represent perfect reactions, the reactions themselves are often not perfect. A reaction does not

### Chemical Proportions in Compounds

Chapter 6 Chemical Proportions in Compounds Solutions for Practice Problems Student Textbook page 201 1. Problem A sample of a compound is analyzed and found to contain 0.90 g of calcium and 1.60 g of