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What does the little number below each Element mean? What are its units? amu/atom.

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Presentation on theme: "What does the little number below each Element mean? What are its units? amu/atom."— Presentation transcript:

1 What does the little number below each Element mean? What are its units? amu/atom

2 What is an amu one amu is defined as 1/12 th of 12 C

3 Average atomic mass or atomic weight is determined by a mass spectroscope. example: Analysis of a sample of carbon was found to have the following isotopes 12 C – % 13 C – % 14 C – % What is the atomic weight of Carbon

4 12 C – (11.999)(.973) = C – (12.998)(.026)= C – (13.966)(.0010)=

5 How much is a mole? How high could you stack a mole of sheets of paper?

6 How much would a mole of iron weigh? Could you lift it? Look on the back inside cover for amu and mole x atoms of Fe 1atom of Fe amu 1 amu x g* =55.85 g

7 What is the Mole? One mole is equal to the number of carbon atoms in exactly grams of C-12: 6.02 x atoms

8 Mole # of atoms or molecules volume of gas Mass of atom or molecule The Shopping Mole 6.02 x atoms or molecules/mole 22.4 L / molex g/ mole

9 Calculate the numbers of atoms of cesium found in 3.57 moles of cesium Calculate the numbers of atoms of cesium found in 3.57grams of cesium Calculate the mass of 4.82 x atoms of cesium

10 Calculating the molar mass of a compound (NH 4 ) 2 S 1. Calculate the mass of 4.65 moles of (NH 4 ) 2 S 2. Calculate the numbers of atoms of nitrogen found in 3.57grams (NH 4 ) 2 S 3. Calculate the mass of nitrogen in 3.76 x formula units of (NH 4 ) 2 S

11 Determining Percent Composition of Compounds Given the compound: Al(HPO 3 ) 3 What are the percent compositions of each of the atoms from which the above compound is constructed? Mass of Aluminum= 1 mol Al mole of Al 26.9 grams Mass of hydrogen = 3 mols H mole of H 1.01 gram Mass of Phosphorus = 3 mols P mole of P 30.9 gram Mass of oxygen = 9 mols O mole of P 16.0 gram = 26.9g Al = 3.03 H = 92.7 g P = 144 g O 266 g Al(HPO 3 ) 3

12 Mass percent of Al: mass of Al mass of Al(HPO 3 ) g 26.9 g 266 g = x 100 = 10.1% Mass percent of H: mass of H mass of Al(HPO 3 ) g 266 g = x 100 = 1.13% Mass percent of P: mass of P mass of Al(HPO 3 ) g 266 g = x 100 = 34.8% Mass percent of O: mass of O mass of Al(HPO 3 ) g 266 g = x 100 = 54.1%

13 Empirical formula A compound is composed of Cl 71.65% and C 24.27% and H 4.07% what is the empirical formula? The Molar mass is 98.96g/mole, what is the molecular formula?

14 Determining the Empirical Formula of a Compound Using Combustion Analysis Combustion Analysis mass difference of H 2 O absorber = g mass difference of CO 2 absorber = g g isopropyl alcohol is combusted

15 mass difference of H 2 O absorber = g mass difference of CO 2 absorber = g grams of H: g H 2 O 18 g H 2 O 1 mole H 2 O 2.02 g H = g H grams of C: g CO 2 44 g CO 2 1 mole CO 2 12 g C = 0.153g C grams of O: g g g H = g

16 C: g C 12 g C 1 mol C = mol C H: g H 1.01 g H 1 mol H = mol C O: g O 16 g O 1 mol O = mol O = 2.97 = 7.91 = 1.00 Assume that the empirical formula for the compound is C 3 H 8 O

17 Ascorbic acid (Vitamin C) contains percent C, 4.58 percent H, and percent O by mass. What is the empirical formula of ascorbic acid? Ethylene glycol, the substance used in automobile antifreeze, is composed of 48.7 % C, 9.7 percent H, and 51.6 percent O by mass. Its molar mass is 62.1 g/mol. (a) What is the empirical formula of ethylene glycol? (b) What is the molecular formula

18 So What is Stoichiometry? mass of A in g mole 3(moles C) C g = mass C A g 1(moles A) mole 1A + 2B 3C + 4D

19 Na 2 SO 3(aq) + 2AgNO 3(aq) Ag 2 SO 3(s) + 2NaNO 3(aq) If 3.4 g of silver nitrate is mixed w/ excess sodium sulfite, what would be the theoretical yield for silver sulfite? a)in moles b)in formula units c)in L at STP d)in grams

20 Na 2 SO 3(aq) + 2AgNO 3(aq) Ag 2 SO 3(s) + 2NaNO 3(aq) If 3.4 g of silver nitrate is mixed sodium sulfite, how many grams of sodium sulfite would you need to react completely?

21 Na 2 SO 3(aq) + 2AgNO 3(aq) Ag 2 SO 3(s) + 2NaNO 3(aq) If 4.5 g of sodium sulfite is mixed w/ excess silver nitrate, what would be the theoretical yield for silver sulfite? What would be the percent yield if 4.1g was produced in the lab?

22 Na 2 SO 3(aq) + 2AgNO 3(aq) Ag 2 SO 3(s) + 2NaNO 3(aq) If 4.3 g of silver nitrate is mixed w/ 3.2g sodium sulfite, what would be the theoretical yield for silver sulfite? How much of the excess reagent is left over?

23 Using Stoichiometry in the Laboratory Na 2 SO 3 (aq) + 2AgNO 3 (aq) Ag 2 SO 3 (s) + 2NaNO 3 (aq) 20 ml 0.35 M 20 ml 0.12 M 1. How many grams of silver sulfite would be produced? 2. What would be the molarity of the sodium nitrate?


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