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1 Chapter 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. 2 1

2 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

3 10.1 What Is a Mole? How is Avogadro s number related to a mole of any substance? A mole (mol) of any substance contains Avogadro s number of representative particles, or representative particles. The term representative particle refers to the species present in a substance: usually atoms, molecules, or formula units. 6 3

4 So a mole is a counted quantity, just like a dozen, only a little bigger! A LOT Mole 8 4

5 10.1 Converting Number of Particles to Moles Simply divide by Avogadro s number

6 3. How many moles is 2.80 x atoms of silicon? Converting Moles to Number of Particles Simply multiple by Avogadro s number. 12 6

7 13 6. How many moles are in 4.65 x molecules of NO 2? 14 7

8 10.1 The Mass of a Mole of an Element How is the atomic mass of an element related to the molar mass of an element?

9 10.1 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, or gram-atomic mass (gram-atom) One molar mass of carbon, sulfur, mercury, and iron are shown. 18 9

10 10.1 The Mass of a Mole of a Compound How is the mass of a mole of a compound calculated? 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 SO 3 has a mass of 80.1 g

11 10.1 Molar Masses of Glucose, Water, and Paradichlorobenzene

12 8. What is the mass of 1.00 mole of sodium hydrogen carbonate? 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

13 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

14 Calculate the mass, in grams, of 2.50 moles of iron (II) hydroxide

15 Calculate the number of moles in 75.0 g of dinitrogen trioxide 30 15

16 10.2 The Mole Volume Relationship What is the volume of a gas at STP? Avogadro s hypothesis states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles

17 10.2 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. Standard temperature and pressure (STP) means a temperature of 0 C and a pressure of kpa, or 1 atmosphere (atm). SEE REFERENCE TABLE A At STP, 1 mol or, 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

18 10.2 Calculating Volume at STP

19 21. At STP, what volume do these gases occupy? a mol He b. O.335 mol C2H Calculating Molar Mass from Density 38 19

20 What is the density of krypton gas at STP? 40 20

21

22 The Mole Road Map 44 22

23 10.3 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 How do you calculate the percent by mass of an element in a compound? 46 23

24 10.3 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%. 47 Section 9.5 The Law of Definite Proportions. In samples of any chemical compound, the masses of the elements are always in the same proportions. The Law of Multiple Proportions Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in small whole number ratios. Ex. H 2 O and H 2 O

25 10.3 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. See reference table T

26 Percent Composition from the Chemical Formula 52 26

27 Calculate the percent composition of these compounds. a.ethane (C 2 H 6 ) b.sodium hydrogen sulfate (NaHSO 4 ) 54 27

28 10.3 Percent Composition as a Conversion Factor You can use percent composition to calculate the number of grams of any element in a specific mass of a compound Propane (C 3 H 8 ) 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 C 3 H

29 10.3 Empirical Formulas What does the empirical formula of a compound show? The empirical formula gives the lowest wholenumber 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 Ethyne (C 2 H 2 ) is a gas used in welder s torches. Styrene (C 8 H 8 ) is used in making polystyrene. Lowest ratio = 1:1 for both compounds These two compounds of carbon have the same empirical formula (CH) but different molecular formulas

30 To determine the empirical formula, find the moles of each element and determine the whole number ratio of each. The whole number ratio is the subscripts in the empirical formula

31 10.3 Molecular Formulas How does the molecular formula of a compound compare with the empirical formula? The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula Methanal, ethanoic acid, and glucose all have the same empirical formula CH 2 O

32 To determine the molecular formula from the empirical formula, find out how many times more massive the molecular mass is than the empirical mass and multiply the empirical formula by this small whole number

33

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