Presentation on theme: "What does the little number below each Element mean? What are its units? amu/atom."— Presentation transcript:
What does the little number below each Element mean? What are its units? amu/atom
What is an amu one amu is defined as 1/12 th of 12 C
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
12 C – (11.999)(.973) = C – (12.998)(.026)= C – (13.966)(.0010)=
How much is a mole? How high could you stack a mole of sheets of paper?
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
What is the Mole? One mole is equal to the number of carbon atoms in exactly grams of C-12: 6.02 x atoms
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
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
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
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
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%
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?
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
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
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
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
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
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
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?
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?
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?
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?