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THE MOLE ... a unit of counting Quantities in Chemical Reactions Big Ideas Relationships in chemical reactions can be described quantitatively The efficiency of chemical reactions can be determined and optimized by applying an understanding of quantitative relationships in such reactions. How Scientists Keep Track of Atoms • One way to measure how much of a substance is available is to count the # of particles in that sample • However, atoms & molecules are extremely small • To solve this problem, scientists developed the concept of the mole • SYMBOL IS n . •*The mole is a unit song The Mole A dozen donuts = 12 A mole of donuts = 6.023x1023 a dozen shoes = 12 A mole of shoes = 6.023x1023 1 mole = 6.02 x 1023 entities of a substance 1 mole of anything = 6.023x1023 = 602,000,000,000,000,000,000,000!!! WHAT IS THE MOLE? FYI…. A formula unit is a term used to represent the lowest whole number ratio of ions in an ionic compound. Different types of particles include: atoms OR molecules OR ions OR electrons OR formula units, etc. Avogadro’s Constant = NA = 6.023 x 1023 particles 1 mol Units of moles are mol On your calculator: EE or EXP or x10^ WHERE DID THIS NUMBER COME FROM? A mole is the amount of substance that contains as many particles as exactly 12.000g of Carbon-12 The Mole- Examples 1 mole of carbon contains 6.02 x 1023 atoms of carbon 1 mole of H2O contains 6.02 x 1023 molecules of H2O 1 mole of NaCl contains 6.02 x 1023 formula units of NaCl How Big is Avogadro’s Number? If you had one mole of dollars, how long would it take to spend it at a rate of $1,000,000 per day? ◦ o 6.02 x 1023 ÷ 1,000,000 = 6.02 x 1017 d 6.02 x 1017 d ÷ 365 d/a = 1.65 x 1015 a Put this into perspective… o The sun is about 4.6 x 109 years old and will burn out in about 5 x 109 years. o You will need to spend faster!! The mole is a BIG number. The green pea analogy puts it into perspective as well: Did you know that 12 pencils will contain a mole of carbon atoms? Variables to Know N • • • n = number of moles n NA N = number of particles NA = Avogadro’s number (6.02 × 1023) • Two possible types of questions: o Moles to Particles o N = n x NA Particles to Moles n = N / NA Using Avogadro’s Constant • • How many atoms in 2 moles of carbon? N = n x NA = 2 moles x (6.02 x 1023) = 1.2 x 1024 particles of C How many moles is 5.0 x 1024 particles of iron? n = N / NA = 5.0 x 1024/6.02 x 1023 = 8.3 moles of Fe • How many atoms in 2 moles of water? N = n x NA = 2 moles x 6.02 x 1023 = 1.2 x 1024 molecules of H2O = 3 atoms per molecule = 3 x (1.2 x 1024 ) = 3.6 x 1024 atoms in 2 moles of H2O LEARNING CHECK (round to 3 sig. figs.) How many molecules of CO2 are in 4.56 moles of CO2? 2.75 x 10 molecules How many moles of water is 5.87 x 1022 molecules? 0.0975 mol (or 9.75 x 10 ) How many moles is 7.7812.9xmoles 1024 formula units of MgCl2 How many atoms of carbon are in 1.23 mol of C6H12O6? 4.44 x 10 atoms C 24 -2 24 Mass to Mole Calculations Atomic Mass ◦ Mass of one atom ◦ Unit μ = atomic mass unit = a.m.u Eg. Each hydrogen atom has a mass of 1.001μ ◦ 1 μ equals approximately 1.67 x 10-24g, which is extremely small and not practical to measure. Enter Molar Mass…. Molar Mass (MM) The mass of 1 mole of a substance Mass of 6.023 x 1023 particles Units are g/mol ◦ Eg. The molar mass of Hydrogen is 1.01 g/mol Molar Mass Molar mass and atomic mass have the same numbers except there is a unit difference. Atomic Mass Molar Mass Li 6.94 μ/atom 6.94 g/mol Ag 107.86 μ/atom 107.86 g/mol The g/mol unit is more useful that μ because… It can be measured in the lab using a scale Example Eg. Find the molar mass of water: H2O H: 2 x 1.001g/mol O: 1 x 16.00 g/mol 18.002g/mol Eg. Find the molar mass of calcium phosphate: Ca3(PO4)2 Ca: 3 x 40.08 g/mol P: 2 x 30.97 g/mol O: 8 x 16.00 g/mol 310.2g/mol The same as: Gram Molecular Mass (for molecules) Gram Formula Mass (ionic compounds) Gram Atomic Mass (for elements) molar mass is just a much broader term than these other specific masses Mole Calculations MM = m/n m n = m/MM MM n m = MMn N = nNA n = N/NA HOMEWORK Complete Moles Worksheet. Try all questions to the best of your ability. Good luck!