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Matt Katz Chapter 6 study guide Calculating mass using Atomic Mass Units (amu): Ex. Calculate the mass, in amu, of a sample of aluminum that contains 75 atoms. 1 Al atom = 26.98 amu Calculating the number of atoms from the mass: Ex. Calculate the number of sodium atoms present in a sample that has a mass of 1172.49 amu. 1 Na atom = 22.99 amu Vocab Atomic mass unit Average atomic mass Mole Avogadro’s number Molar mass Mass percent Empirical formula Molecular formula A small unit of mass used to describe the mass of an atom. It is abbreviated as amu. Most elements have different isotopes with different masses. Because of this all elements are listed with the weighted averages of their different masses. The unit all chemists use in describing numbers of atoms. It is abbreviated as (mol). Ex. It is the number equal to the number of carbon atoms in 12.01 grams of carbon. 6.022 > one mole of something consists of this many units of that substance. The mass (in grams) of 1 mol of the substance. The simplest whole-number ratio of the atoms present in the compound. It can be derived from the percent composition of the compound. The exact formula of the molecules present. It is always an integer multiple of the empirical formula. Questions: 1) Calculate the mass of 0.25 moles of water. 2) Calculate the moles in 124.5g of oxygen gas. 3) Calculate the molecular mass of a pure substance if 1.75 moles of the substance has a mass of 29.792g 4) 5) 6) 7) 8) Calculate the mass of 1 mole of CO2. Calculate the mass of 1 mole of SO2. What is the molar mass of NH4F? What is the mass in grams of 6.02 x 1023 molecules of CO? Calculate the mass in grams of 3.01 x 1023 molecules of F2. 9) Determine the mass, in grams, of one gold atom. One mole of gold atoms has a mass of 197 grams. 10) How many moles are present in each of the following: (a) 36.0 grams of water (H2O)? (b) 8.5 grams of ammonia (NH3)? (c) 6.35 grams of copper? (d) 2.16 grams of silver? (e) 0.85 grams of silver nitrate (AgNO3)? (f) 7.10 grams of chlorine gas? 11) What is the mass, in grams, of each of the following? (a) 1.00 mole of sulfur dioxide? (b) 2.5 moles of carbon monoxide? (c) 0.10 mole of hydrogen fluoride? (d) 0.50 mole of oxygen gas? (e) 0.50 mole of aluminium? (f) 0.040 mole of trisodium phosphate (Na3PO4)?