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Chapter 10 Chemical Quantities Hingham High School Mr. Clune.

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1 Chapter 10 Chemical Quantities Hingham High School Mr. Clune

2 What is a Mole? What is a Mole? You can measure mass, or volume, or you can count pieces. We measure mass in grams. We measure volume in liters. We count pieces in MOLES.

3 Moles (abbreviated: mol) Defined as the number of carbon atoms in exactly 12 grams of carbon mole is 6.02 x particles. 1 mole is 6.02 x particles. Treat it like a very large dozen 6.02 x is called Avogadro’s number.

4 Representative particles The smallest pieces of a substance. –For a molecular compound: it is the molecule. –For an ionic compound: it is the formula unit (ions). –For an element: it is the atom. Remember the 7 diatomic elements (made of molecules)

5 Types of questions How many oxygen atoms in the following? –CaCO 3 –Al 2 (SO 4 ) 3 How many ions in the following? –CaCl 2 –NaOH –Al 2 (SO 4 )

6 Measuring Moles Remember relative atomic mass? The amu was one twelfth the mass of a carbon-12 atom. The amu was one twelfth the mass of a carbon-12 atom. Since the mole is the number of atoms in 12 grams of carbon-12, The decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.

7 Molar Mass Equals the mass of 1 mole of an element in grams grams of C has the same number of pieces as grams of H and grams of iron. We can write this as g C = 1 mole C We can count things by weighing them.

8 Examples How much would 2.34 moles of carbon weigh? 1 mole of C is 12.01g or g/mole g/mole 2.34 mole g mole moleX = g

9 Examples How many moles of magnesium is g of Mg? 1 mole of Mg is 24.31g or g/mole g/mole g X 1 mole g = 1 mole

10 Examples How many atoms of lithium is 1.00 g of Li? 6.94g/mol e 6.02x10 23 atoms mole mole1.00g X 1 mole 6.94g 6.02x10 23 atoms mole moleX 8.67x10 22 atom s

11 6.02x10 23 atoms mole moleX g/mol e 1 mole 6.02x10 23 at m X 13.6g How much would 3.45 x atoms of U weigh? 3.45x10 22 at m g mole

12 What about compounds? To find the mass of one mole of a compound  determine the moles of the elements they have  Find out how much they would weigh  add them up

13 What about compounds? 1 mole of H 2 O molecules has two moles of H atoms and 1 mole of O atoms H2OH2OH2OH2O

14 What about compounds? H:2 moles X 1.08g/mole = 2.16g H2OH2OH2OH2O O:1 mole X 16.00g/mole= 32.00g + 1 mole of H 2 0 = 34.16g 1 mole of H 2 0 = 34.16g

15 What about compounds? What is the mass of one mole of CH 4 ? 1 mole CH 4 = 16.05g 1 mole of C x g = 12.02g 4 mole of H x 1.01 g = 4.04g +

16 What about compounds? The Molar Mass of CH 4 is 16.05g –this is the mass of one mole of a molecular compound.

17 Moles to Mass Conversions How many grams of Na are there in 1.23 moles? 1. How many grams of Na are there in 1 mole? 22.99g/mol 2. How many grams of Na are there in 1.23 moles? 1.23 mol g mol X = 28.28g

18 Moles to Mass Conversions How many grams of C 6 H 12 O 6 are there in 0.56 moles? 1. How many grams of C 6 H 12 O 6 are there in 1 mole? g/mol C: 6 x 12.01g = 72.06g H: 12 x 1.01g = 12.12g O: 6 x 16.00g = 96.00g +

19 Moles to Mass Conversions 2. How many grams of C 6 H 12 O 6 are there in 0.56 moles? 0.56mol g mol X = 28.28g

20 Representative Particles How many moles of water is 5.87 x molecules? Moles 1 mole 6.02 x molecules 5.87 x molecules X = moles or 9.8 x moles

21 How many molecules of CO 2 are there in 4.56 moles of CO 2 ? 4.56 mol 4.56 mol 6.02 x molecules 1 mol X = 2.75 x molecules 2.75 x molecules

22 How many atoms of carbon are there in 1.23 moles of C 6 H 12 O 6 ? 1.23 mol 1.23 mol 6.02 x molecules 1 mol X = 7.40 x molecule 6 atoms of C 1 molecule X = 4.44 x atoms of C

23 How many moles is 7.78 x formula units of MgCl 2 ? 1 mole 6.02 x molecules 7.78 x molecules X = moles

24 What is the weight of 3.01 x molecules of NaOH? 1 mole 6.02 x molecules 3.01 x molecules X = 5.00 moles 1. Find the number of moles.

25 2. Find the mass of one mole of NaOH. Na : 1 x = 22.99g O : 1 x = 16.00g O : 1 x = 16.00g H : 1 x 1.08 = 1.08g H : 1 x 1.08 = 1.08g g 40.07g

26 3. Find the mass of 5 moles of NaOH. 5 mol 40.07g 1 mol X = g

27 Homework 10-1 Practice Problems Worksheet 1-16 Due: 01/10/05

28 Molar Mass Molar mass is the generic term for the mass of one mole of any substance (in grams) The same as: 1) gram molecular mass, 2) gram formula mass, and 3) gram atomic mass- just a much broader term.

29 Examples Calculate the molar mass of the following and tell what type it is: Na 2 S N2O4N2O4N2O4N2O4C Ca(NO 3 ) 2 C 6 H 12 O 6 (NH 4 ) 3 PO 4

30 Molar Mass The number of grams of 1 mole of atoms, ions, or molecules. We can make conversion factors from these. –To change grams of a compound to moles of a compound.

31 For example How many moles is 5.69 g of NaOH?

32 For example How many moles is 5.69 g of NaOH?

33 For example How many moles is 5.69 g of NaOH? l need to change grams to moles

34 For example How many moles is 5.69 g of NaOH? l need to change grams to moles l for NaOH

35 For example How many moles is 5.69 g of NaOH? l need to change grams to moles l for NaOH l 1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g

36 For example How many moles is 5.69 g of NaOH? l need to change grams to moles l for NaOH l 1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g l 1 mole NaOH = g

37 For example How many moles is 5.69 g of NaOH? l need to change grams to moles l for NaOH l 1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g l 1 mole NaOH = g

38 For example How many moles is 5.69 g of NaOH? l need to change grams to moles l for NaOH l 1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g l 1 mole NaOH = g

39 Gases Many of the chemicals we deal with are gases. –They are difficult to weigh. Need to know how many moles of gas we have. Two things effect the volume of a gas –Temperature and pressure We need to compare them at the same temperature and pressure.

40 Standard Temperature and Pressure 0ºC and 1 atm pressure abbreviated STP At STP 1 mole of gas occupies 22.4 L Called the molar volume 1 mole = 22.4 L of any gas at STP

41 Examples What is the volume of 4.59 mole of CO 2 gas at STP? 4.59 mol 22.4 L 1 mol X= L

42 Examples How many moles is 5.67 L of O 2 at STP? 5.67 L 1 mol 22.4 L X= 0.25 mol

43 What is the volume of 8.8 g of CH 4 gas at STP? 1. Find the molar mass of CH 4. C: 1 X = 12.01g H: 4 X 1.01 = 4.04g g 2. Find the number of moles. 8.8g X 1 mol 16.05g= 0.55 mol

44 What is the volume of 8.8 g of CH 4 gas at STP? 3. Find the volume of CH L 1 mol 0.55 mol X = L

45 Mole Volume MassParticle 1 mol molar mass 1 mol 22.4L 1 mol 22.4L 1 mol 6.02X10 23 part. 1 mol

46 Homework Finish worksheet. Due: 1/11/05 Quiz on Conversions

47 Density of a gas D = m / V D = m / V –for a gas the units will be g / L We can determine the density of any gas at STP if we know its formula. To find the density we need the mass and the volume. If you assume you have 1 mole, then the mass is the molar mass (from PT) At STP the volume is 22.4 L.

48 Examples Find the density of CO 2 at STP. Find the density of CH 4 at STP.

49 The other way Given the density, we can find the molar mass of the gas. Again, pretend you have 1 mole at STP, so V = 22.4 L. m = D x V m is the mass of 1 mole, since you have 22.4 L of the stuff. What is the molar mass of a gas with a density of g/L? 2.86 g/L? 2.86 g/L?

50 Summary These four items are all equal: a) 1 mole b) molar mass (in grams) c) 6.02 x representative particles d) 22.4 L at STP Thus, we can make conversion factors from them.

51 Section 10.3 Percent Composition and Chemical Formulas OBJECTIVES: –Calculate the percent composition of a substance from its chemical formula or experimental data.

52 Section 10.3 Percent Composition and Chemical Formulas OBJECTIVES: –Derive the empirical formula and the molecular formula of a compound from experimental data.

53 Calculating Percent Composition of a Compound Like all percent problems: Part X 100% Part X 100% whole whole Find the mass of each component, Then divide by the total mass.

54 Example Calculate the percent composition of a compound that is g of Ag with 4.30 g of S. 1. Calculate the total mass. Ag + S = 29.00g g = 33.30g

55 Example 2. Calculate % of each element g33.3g X 100% = 87% Ag 4.30g33.3g X 100% = 13% S

56 Getting it from the formula If we know the formula, assume you have 1 mole. Then you know the mass of the pieces and the whole. Find the Molar Mass.

57 Examples Calculate the percent composition of C 2 H 4. C: 2 x 12.0 = 24.0g H: 4 x 1.0 = 4.0g Total Mass = 28.0g +

58 Example 2. Calculate % of each element. 24.0g28.0g X 100% = 86% C 4.0g28.0g X 100% = 14% H

59 Examples If a substance which has a mass of 0.85g is 75% C and 25% 0, how much of each substance is there? C: 0.85g X.75 =0.64g O: 0.85g X.25 =0.21g

60 Homework Worksheet Show all work in Notebook!!!! Due: 2/01/06 Quiz: 2/2/06

61 The Empirical Formula The lowest whole number ratio of elements in a compound. The molecular formula = the actual ratio of elements in a compound. The two can be the same.

62 The Empirical Formula CH 2 is an empirical formula C 2 H 4 is a molecular formula C 3 H 6 is a molecular formula H 2 O is both empirical & molecular

63 Calculating Empirical Just find the lowest whole number ratio C 6 H 12 O 6 CH 4 N - CH 2 O - CH 4 N

64 Calculating Empirical It is not just the ratio of atoms, it is also the ratio of moles of atoms. In 1 mole of CO 2 there is 1 mole of carbon and 2 moles of oxygen. In one molecule of CO 2 there is 1 atom of C and 2 atoms of O.

65 Calculating Empirical We can get a ratio from the percent composition. Assume you have a 100 g. The percentages become grams. Convert grams to moles. Find lowest whole number ratio by dividing by the smallest.

66 Calculate the empirical formula of a compound composed of % C, % H, and %N. Assume 100 g so: C: 38.67g x 1mol = 3.22 mol C 12.0g 12.0g H g x 1mol = mol H 1.0g N: 45.11g x 1mol = 3.22 mol N 14.0g

67 The Smallest number is 3.22mol. Divide each mole value by 3.22mol.

68 The ratio of C:N 3.22 mol C = 1 mol C 3.22 mol C = 1 mol C 3.22 mol N 1 mol N 3.22 mol N 1 mol N The ratio H:N mol H = 5 mol H 3.22 mol N 1 mol N mol H = 5 mol H 3.22 mol N 1 mol N C1H5N1C1H5N1C1H5N1C1H5N1

69 A compound is % P and % O. What is the empirical formula? Assume 100g & find moles g X1mol30.97g= 1.41 mol P: 56.36g X1mol16.00g= 3.52 mol O:

70 Find ratio of moles. Ratio of P:O 1.41 mol of P 3.52 mol of O 2 of P 2 of P 5 of O = P2O5 P2O5 P2O5 P2O5 Empirical Formula

71 Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula? Example Assume 100g & find moles.

72 28.87g X1mol14.0g= 2.06 mol N: 16.49g X1mol16.0g= 1.03 mol O: 5.15g X1mol1.0g= 5.10 mol H:49.48gX1mol12.0g= 4.12 mol C:

73 Find ratio of moles. Ratio of C:H:N:O 4.12 mol of C 1.03 mol of O 4 of C 4 of C 1 of O = 5.10 mol of H 1.03 mol of O 5 of H 5 of H 1 of O = 2.06 mol of N 1.03 mol of O 2 of N 2 of N 1 of O =

74 Find ratio of moles. Ratio of C:H:N:O C4H5N2O C4H5N2O C4H5N2O C4H5N2O 4:5:2:1 4:5:2:1 Empirical Formula

75 Empirical to molecular Since the empirical formula is the lowest ratio, the actual molecule would weigh more. By a whole number multiple. Divide the actual molar mass by the empirical formula mass. Caffeine has a molar mass of 194 g. what is its molecular formula?

76 Example A compound is known to be composed of % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) to be g. What is its molecular formula?

77 71.65g X1mol35.45g= 2.02 mol Cl: 4.07g X1mol1.01g= 4.03 mol H: 24.27g X1mol12.01g= 2.02 mol C: Assume 100g & find moles.

78 Find ratio of moles. Ratio of Cl:C:H 2.02 mol of Cl 2.02 mol of C 1 of Cl 1 of Cl 1 of C = 4.03 mol of H 2.02 mol of C 2 of H 2 of H 1 of C = CH 2 Cl CH 2 Cl Empirical Formula

79 Find the mass of the empirical formula. CH 2 Cl CH 2 Cl C: 1 X 12.01g = 12.01g H: 2 X 1.01g = 2.02g Cl: 1 X 35.45g = 35.45g g 49.48g

80 Compare to the molar mass of the molecular formula g for CH 2 Cl 49.48g for CH 2 Cl Empirical Formula 98.96g for 98.96g for Molecular Formula C 2 H 4 Cl 2

81 Homework Worksheet – 25 Due: 2/2/06 Quiz: 2/2/06

82 Homework Worksheet 10-3 Finish Due: 1/18/05 Test: 1/18/05

83


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