Calculate the number of atoms of silicon in 0.367 moles of silicon. a) 6.10 x 10-25 atoms Si b) 2.21 x 10 23 atoms Si c) 2.21 atoms Si d)1.64 x 10 24 atoms Si What do you need ? Avogadro’s Number 1 mole = 6.02 x 10 23 atoms 0.367 mol x 6.02 x 10 23 atoms / 1 mol = 2.21 x 10 23 atoms Si

Calculate the molar mass of potassium phosphate. a) 134 g/mol b) 86.07 g/mol c) 134.07 g/mol d) 212.27 g/mol What do you need ? 1) Formula of potassium phosphate: K3PO4 2) Atomic Weights (molar mass) K = 39.10, P = 30.97, O = 16.00 3(39.10) + 30.97 + 4(16.00) = 212.27 g/mol

Calculate the mass in grams of 4.00 moles of sulfur. a) 128 g b) 128.3 g c) 12.5 g d) 0.125 g What do you need ? Atomic Weight sulfur (S) = 32.07 (molar mass) = 32.07 g/mol 4 mol sulfur x 32.07 g/mol sulfur = 128.3 g

How many moles is 146.3 grams of nickel? a) 2.49 mol b) 0.4012 mol c) 2.493 mol d) 8586 mol What do you need ? Atomic Weight (Ni) = 58.69 (molar mass Ni) = 58.69 g/1 mol 146.3 g Ni x 1 mol Ni / 58.69 g Ni = 2.493 mol

Calculate the molar mass of methane gas if 1 Calculate the molar mass of methane gas if 1.00 g of methane occupies a volume of 1.39 L at STP. a) 22.4 g/mol b) 16.1 g/mol c) 1.39 g/mol d) 0.719 g/mol What do you need ? 1 mole of a gas @ STP = 22.4 L 1 mol / 22.4 L = x mol / 1.39 L x mol = 1.39 L . mol / 22.4 L x mol = 0.0621 mol 1.00 g / 0.0621 mol = 16.1 g/mol

Calculate the percentage composition for all the elements in nicotine, C10H14N2. a) 64.14% C, 14.04% H, 21.82% N b) 74.017 % C, 8.714 % H, 17.27 % N c) 74.02 % C, 8.71 % H, 17.27 % N d) 44.43 % C, 3.74 % H, 51.83 % N What do you need ? Molar mass C10H14N2 C = 12.01, H = 1.01, N = 14.01 10(12.01) + 14(1.01) + 2(14.01) = 162.26 g/mol 120.1g/mol 14.14 g/mol 28.02 g/mol 120.1/ 162.26 14.14 / 162.26 28.02 / 162.26 x 100 = x 100 = x 100 = 74.02% 8.71% 17.27%

Freon was used commonly as a refrigerant until CFCs were found to deplete the ozone layer. An analysis of freon gave the following data: 9.93% carbon, 58.64% chlorine, and 31.43% fluorine. What is the empirical formula of freon, CxClyFz? What do you need ? Atomic masses: C = 12.01, Cl = 35.45, F = 19.00 Calculate respective moles: 9.93g/12.01 g/mol * 58.64 g/ 35.45 g/mol * 31.43 g /19.00 g/mol 0.827mol 1.654 mol 1.654 mol CxClyFz = C0.827Cl1.654 F1.654 C1Cl2F2 0.827 0.827 0.827 CCl2F2

In an experiment, 5. 00 g of tungsten reacts with air to give 6 In an experiment, 5.00 g of tungsten reacts with air to give 6.31 g of tungsten oxide. What is the empirical formula of tungsten oxide? W3O8 W5O6 WO3 WO What do you need ? Equation for Reaction: x W(s) + y/2 O 2 (g) WxOy (s) Mass of O2 6.31 g - 5.00g = 1.31g Atomic masses: W = 183.85, O = 16.00 Calculate respective moles: 5.00/183.85 g/mol * 1.31 g /16.00 g/mol 0.0272mol 0.0819 mol WxOy = W0.0272 O 0.0819 W1 O 3.01 0.0272 0.0272 W O 3

A student calculated the relative number of moles for several different compounds as follows. What are the correct empirical formulas? Al1 O 1.511 Al2 O 3 aluminum oxide K3.012P1O3.973 K3PO4 potassium phosphate N1 O 2.501 N2 O5 dinitrogen pentoxide C1.002H1.331O1.006 C3H4O3 pyruvic acid C1.012H2.001O1.009 CH2O formaldehyde

A student calculated an empirical formula of CH2O for an unknown white solid. The solid could possibly be several different compounds: formaldehyde, lactic acid, erythrose, ribose or glucose. Mass spectrometry results indicated a molar mass of 90.08 g/mol. What is the correct molecular formula of the solid? CH2O formaldehyde C3H6O3 lactic acid C4H8O4 erythrose C5H10O5 ribose C6H12O6 glucose What do you need ? Molar mass CH2O = 30.03 g/mol C = 12.01, H = 1.01, O = 16.00 Compare molar masses: 90.08 g/mol / 30.03 g/mol = 3 3 x (C1H2O1) = C3H6O3 lactic acid