Ch. 10: Chemical Quantities 10.1 The mole: a measurement of matter Avogadro’s number, mass of a mole| 10.2 Mole-mass and mole-volume relationships STP 10.3 Percent composition (skip empirical formulas)

10.1 The Mole: A Measurement of Matter You could measure the amount of sand in a sand sculpture by counting each grain of sand, but it would be much easier to weigh the sand. You’ll discover how chemists measure the amount of a substance using a unit called a mole, which relates the number of particles to the mass.

10.1 Measuring Matter What are three methods for measuring the amount of something? You often measure the amount of something by one of three different methods—by count, by mass, and by volume.

Sample problem 10.1 Use dimensional analysis:

for Sample Problem 10.1 #1 on worksheet

10.1 What is a Mole? One mole (mol) of a substance is 6.02  1023 representative particles of that substance and is the SI unit for measuring the amount of a substance. A mole of any substance contains Avogadro’s number of representative particles, or 6.02  1023 representative particles. The term representative particle refers to the species present in a substance: usually atoms, molecules, or formula units.

10.1 What is a Mole?

Sample problem 10.2

Sample Problem 10.2 #4 on worksheet On your calculator be sure to put the denominator in parentheses or divide by both 6.02 and 1023

Sample problem 10.3

10.3

Sample Problem 10.3 #5 on worksheet Sample problem 10.3

The Mass of a Mole of an Element 10.1 The Mass of a Mole of an Element The atomic mass of an element expressed in grams is the mass of a mole of the element. The mass of a mole of an element is its molar mass. Ex. On the periodic table, carbon has a mass of 12.011 amu. We say 12 grams per mole or just 12 grams.

The Mass of a Mole of an Element 10.1 The Mass of a Mole of an Element One molar mass of carbon, sulfur, mercury, and iron are shown. One molar mass of carbon, sulfur, mercury, and iron are shown. Each of the quantities contains one mole of the element. Applying Concepts How many atoms of each element are shown?

The Mass of a Mole of an Element 10.1 The Mass of a Mole of an Element

The Mass of a Mole of a Compound 10.1 To calculate the molar mass of a compound, find the number of grams of each element in one mole of the compound. Then add the masses of the elements in the compound. Substitute the unit grams for atomic mass units. Thus 1 mol of SO3 has a mass of 80.1 g.

The Mass of a Mole of a Compound 10.1 The Mass of a Mole of a Compound Molar Masses of Glucose, Water, and Paradichlorobenzene One molar mass is shown for each of three molecular compounds. Inferring How can you know that each sample contains Avogadro’s number of molecules?

Sample problem 10.4

Sample Problem 10.4 #7 on worksheet phosphorus molar mass = 30.974 g chlorine molar mass = 35.453 g 1 mole of phosphorus = 30.974 g 3 mole of chlorine = 3 x 35.453 = 106.359 g molar mass of PCl3 = 30.974 + 106.359 = 137 g/mol

10.1 Section Quiz. 1. Three common ways of measuring the amount of something are by count, by mass, and a. by temperature. b. by volume. c. by area. d. by density.

10.1 Section Quiz. 2. A mole of hydrogen gas, H2(g), contains 6.02 x 1023 a. molecules. b. atoms. c. amu. d. grams.

10.1 Section Quiz. 3. The atomic mass of fluorine is 19.0 amu, so the molar mass is a. 19.0 amu. b. 19.0 g. c. 6.02 x 1023 amu. d. 6.02 x 1023 g.

10.1 Section Quiz. 4. Calculate the molar mass of ammonium nitrate. a. 45.02 g b. 80.05 g c. 60.06 g d. 48.05 g NH4NO3 14+4(1)+14+3(16) g

10.2 Mole–Mass and Mole–Volume Relationships How can you guess the number of jelly beans in a jar? You estimate the size of a jelly bean and then estimate the dimensions of the container to obtain its volume. In a similar way, chemists use the relationships between the mole and quantities such as mass, volume, and number of particles to solve chemistry problems.

The Mole–Mass Relationship 10.2 The Mole–Mass Relationship How do you convert the mass of a substance to the number of moles of the substance? Use the molar mass of an element or compound to convert between the mass of a substance and the moles of a substance.

Sample problem 10.5 These aluminum satellite dishes at the National Radio Astronomy Observatory near Soccoro, New Mexico are naturally protected from corrosion by the formation of a thin film of aluminum oxide (Al2O3).

Sample Problem 10.5 #9 on worksheet mass of carbon= 20 x 12.011 = 240.22 g mass of hydrogen = 42 x 1.008 = 42.336 g mass of C20H42 = 282.556 g/mol

Sample problem 10.6 Rust weakens an iron chain.

Sample Problem 10.6 #11 on worksheet

The Mole–Volume Relationship 10.2 The Mole–Volume Relationship Avogadro’s hypothesis states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. Standard temperature and pressure (STP) means a temperature of 0°C or 273 K and a pressure of 101.3 kPa (kilopascals) or 1 atmosphere (atm). In each container, the volume occupied by the gas molecules is small compared with the container’s volume, so the molecules are not tightly packed. a) The molecules in this container are small. b) This container can accommodate the same number of larger molecules. The volume of a gas varies with temperature and pressure. Because of these variations, the volume of a gas is usually measured at a standard temperature and pressure.

The Mole–Volume Relationship 10.2 The Mole–Volume Relationship At STP, 1 mol or, 6.02  1023 representative particles, of any gas occupies a volume of 22.4 L. The quantity 22.4 L is called the molar volume of a gas. This box, with a volume of 22.4 L, holds one mole of gas at STP.

10.7

10.7

Sample Problem 10.7 #13 on worksheet

The Mole–Volume Relationship 10.2 The Mole–Volume Relationship Calculating Molar Mass from Density

Sample problem 10.8

Sample Problem 10.8 #15 on worksheet

10.2 The Mole Road Map The map shows the conversion factors needed to convert among volume, mass, and number of particles. Interpreting Diagrams How many conversion factors are needed to convert from the mass of a gas to the volume of a gas at STP?

10.2 The Mole Road Map The map shows the conversion factors needed to convert among volume, mass, and number of particles. Interpreting Diagrams How many conversion factors are needed to convert from the mass of a gas to the volume of a gas at STP?

10.2 The Mole Road Map The map shows the conversion factors needed to convert among volume, mass, and number of particles. Interpreting Diagrams How many conversion factors are needed to convert from the mass of a gas to the volume of a gas at STP?

The Mole Road Map 10.2 p. 303 in textbook The map shows the conversion factors needed to convert among volume, mass, and number of particles. Interpreting Diagrams How many conversion factors are needed to convert from the mass of a gas to the volume of a gas at STP?

10.2 Section Quiz. 1. Calculate the mass in grams of a sample containing 1.85 x 1034 molecules of water. a. 3.07 x 1010 g b. 5.53 x 1011 g c. 188 g d. 8.46 x 103 g

10.2 Section Quiz. 2. Calculate the number of moles in a spoonful of table sugar (C12H22O11) having a mass of 10.5 g. a. 32.6 mol b. 3.59  103 mol c. 3.07  10–3 mol d. 1.85  1022 mol

10.2 Section Quiz. 3. What is the volume of 0.35 mol of oxygen gas at STP? a. 32 L b. 64 L c. 7.8 L d. 16 L

10.3 Percent Composition and Chemical Formulas It helps to know the percents of the components in a shirt because they affect how warm it is, whether it will need to be ironed, and how it should be cleaned. You will learn how the percents of the elements in a compound are important in chemistry.

The Percent Composition of a Compound Percent Composition from Mass Data The relative amounts of the elements in a compound are expressed as the percent composition or the percent by mass of each element in the compound.

The Percent Composition of a Compound 10.3 The Percent Composition of a Compound How do you calculate the percent by mass of an element in a compound? The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%. Potassium chromate (K2CrO4 ) is composed of 40.3% potassium, 26.8% chromium, and 32.9% oxygen. Interpreting Diagrams How does this percent composition differ from the percent composition of potassium dichromate (K2Cr2O7), a compound composed of the same three elements?

Sample problem 10.9

Sample Problem 10.9 #18 on worksheet

The Percent Composition of a Compound 10.3 The Percent Composition of a Compound Percent Composition from the Chemical Formula

Sample Problem 10.10 #20 on worksheet nitrogen mass is 14.007 g/mol hydrogen mass is 1.008 g/mol NH3 mass is 14.007+3(1.008)=17.031 g/mol

NH4NO3 nitrogen mass = 14. 007 x 2 = 28. 014 g hydrogen mass = 1 NH4NO3 nitrogen mass = 14.007 x 2 = 28.014 g hydrogen mass = 1.008 x 4 = 4.032 g oxygen mass = 16.000 x 3 = 48.000 g mass of NH4NO3 = 80.046 g

The Percent Composition of a Compound 10.3 You can use percent composition to calculate the number of grams of any element in a specific mass of a compound. Propane (C3H8) is 81.8% carbon and 18% hydrogen. You can calculate the mass of carbon and the mass of hydrogen in an 82.0 g sample of C3H8.

10.3 Empirical Formulas The empirical formula gives the lowest whole-number ratio of the atoms of the elements in a compound. The empirical formula of a compound shows the smallest whole-number ratio of the atoms in the compound.

10.3 Empirical Formulas Ethyne (C2H2) is a gas used in welder’s torches. Styrene (C8H8) is used in making polystyrene. These two compounds of carbon have the same empirical formula (CH) but different molecular formulas. Ethyne (C2H2), also called acetylene, is a gas used in welder’s torches. Styrene (C8H8) is used in making polystyrene. These two compounds have the same empirical formula. Calculating What is the empirical formula of ethyne and styrene?

10.3 Molecular Formulas Methanal, ethanoic acid, and glucose all have the same empirical formula—CH2O. Methanal (formaldehyde), ethanoic acid (acetic acid), and glucose have the same empirical formula. Applying Concepts How could you easily obtain the molar mass of glucose using the molar mass of methanal?

10.3 Section Quiz. a. 67.4% C b. 58.8% C c. 51.7% C d. 68.2% C 1. Calculate the percent by mass of carbon in cadaverine, C5H14N2, a compound present in rotting meat. a. 67.4% C b. 58.8% C c. 51.7% C d. 68.2% C

10.3 Section Quiz. 3. Determine the molecular formula of a compound that contains 40.0 percent C, 6.71 percent H, and 53.29 percent O and has a molar mass of 60.05 g. a. C2H4O2 b. CH2O c. C2H3O d. C2H4O

Ch. 10—What you need to know  Ch. 10 worksheet problems—Converting using Avogadro’s number, molar mass, and molar volume Who is Counting? Lab % Composition of a Penny Lab  Measure by count, mass, volume Avogadro’s number, mole, representative particles Atomic mass, molar mass, molar volume Mole-mass, mole-volume relationships STP (standard temperature and pressure; 0º C or 273 K and 101.3 kPa or 1 atm) Pa is a unit of pressure--pascals Mole—SI unit of measure for amount of a substance Percent composition The majority of the quiz is calculations. Be able to show work using dimensional analysis (“railroad tracks”) and include units.