1.1 Moles and Molar Mass PDF

1.1 TOPIC: 1.1 MOLES AND MOLAR MASS ENDURING UNDERSTANDING: SPQ-1 The mole allows different units to be compared LEARNING OBJECTIVE: SPQ-1.A Calculate quantities of a...

1.1 TOPIC: 1.1 MOLES AND MOLAR MASS ENDURING UNDERSTANDING: SPQ-1 The mole allows different units to be compared LEARNING OBJECTIVE: SPQ-1.A Calculate quantities of a substance or its relative number of particles using dimensional analysis and the mole concept. ESSENTIAL KNOWLEDGE: SPQ-1.A.1 One cannot count particles directly while performing laboratory work. Thus, there must be a connection between the masses of substances reacting and the actual number of particles undergoing chemical changes. SPQ-1.A.2 Avogadro’s number (NA = 6.022 x 1023 particles/mole) provides the connection between the number of moles in a pure sample of a substance and the number of constituent particles (or formula units) of that substance. SPQ-1.A.3 Expressing the mass of an individual atom or molecule in atomic mass units (amu) is useful because the average mass in amu of one particle (atom or molecule) or formula unit of a substance will always be numerically equal to the molar mass of that substance in grams. Thus, there is a quantitative connection between the mass of a substance and the number of particles that the substance contains. EQUATION(S): n = m/M moles = mass/molar mass NOTES: It is impractical to count atoms as they are so small, so in chemistry we can “count” atoms by weighing them or measuring them in some other way. We need to convert the measurements that we make into numbers of atoms so that we can be sure to react the right amounts of materials. Atomic masses are measured in atomic mass units, amu, which is a relative unit, based on the carbon-12 isotope being assigned a mass of exactly 12 grams per mole. A mole is a term used to describe a group of atoms containing 6.022 x 1023 items. Chemists use moles to discuss amounts of atoms because using the actual amount of atoms is such a large number it is often impractical. You can calculate the mass for one mole of a substance by referring to the periodic table to find the average atomic mass of each atom then adding up the total mass for the formula. Calculate the molar mass of dinitrogen tetroxide: How to calculate Molar Mass: N2O4 1) List the atoms 2) Count the atoms N = 2 x 14.0067 = 28.0134 3) Find the mass of each atom from the periodic table O = 4 x 15.9994 = 63.9976 4) Multiply the number of atoms (#2) by the mass of each atom (#3) 92.0110 g/mole 5) Add together the values (#4) Molar mass can be used as a conversion factor to convert between moles and grams. It is unique for each sample. Avogadro’s Number, 6.022 x 1023 particles/mole, is the conversion factor to convert between number of particles (molecules, atoms, formula units, ions) and moles. Number of Mass Moles Avogadro’s Molar Particles Mass number 1 1.1 I DO: How many moles of Lead (II) iodide, PbI2, are there in a 25.0 gram sample? 25.0 g PbI2 x 1 mole = 0.0542 mole PbI2 461.0g How many atoms of lead, Pb, are in the sample? 0.0542 moles PbI2 x 1 mol Pb x 6.022 x 1023 atoms Pb = 3.27 x1022 atoms Pb 1 mole PbI2 1 mole Pb WE DO: A 0.244 g sample of calcium carbonate, CaCO3, was recovered from a sample of hard water. How many formula units of CaCO3 were in the sample? YOU DO: 1) Methane, CH4, is the gas commonly found in labs to fuel Bunsen burners. a) How many moles of methane are there in a 7.21 gram sample? b) How many particles of methane are there in the sample? c) How many atoms of hydrogen are found in the sample? 2) Helium, He, is used in balloons, deep sea diving tanks, and in industry. While it is the second most abundant element in the universe, in 2019 there was a shortage of helium which caused the prices to rise. If 150. grams of helium is needed to cool a superconductor, how many atoms of helium are used? 3) If you know the mass and identity of a sample, what other information do you need in order to find the number of each atom in the sample? 4) Given 10.0 gram samples of LiCl, LiBr, LiF and LiI, place the samples in order of least to greatest number of atoms of Lithium, Li. 5) What is the mass of one atom of carbon-12? 6) What is the mass of 2.30 x 1024 particles of water, H2O? 7) Which is a greater mass, 0.25 moles of carbon dioxide, CO2, or 1.5 x 1023 particles of carbon monoxide, CO? 2