Transcript mole
Stoichiometry The mathematics of Chemistry What is Stoichiometry? The proportional relationship between two or more substances during a chemical reaction. In other words, using dimensional analysis to convert one substance to another There are many different types, but they are all similar. So, let’s start small. How small? We know an atom is extremely small, but how small is an atom? In other words, how small is the smallest particle of an element that retains the properties of the element? World Population: about 6000000000 Number of atoms in a penny: about 29700000000000000000000 or 2.97 x 1022 How do we get that number? By using Avogadro's Number 6.02 x 1023 and using dimensional analysis again What is Avogadro’s Number? It is 6.02 x 1023 atoms per mole What is a mole? The number of atoms in exactly 12 grams of carbon-12 and it is the SI unit for the amount of a substance Example problems – 6.33 x 1024 atoms of C are how many moles? – How many atoms of Zn are in 3.5 moles? The mole is also related to molar mass Molar Mass – the mass in grams of 1 mol of an element, ion, compound, etc. Represented by g/mol (what we did last class) Example problems – 92.6 g of CO2 equals how many moles? – 1.25 moles of S8 equals how many grams? Atomic Mass Units verses Molar Mass The mass in grams of 1 mol of an element is numerically equal to the element’s atomic mass from the periodic table in atomic mass units. In other words, 1 g/mol = 1 amu They are interchangeable Putting it all together. Let’s look at our penny again How did they get that number for the number of Cu atoms in a penny? A penny has an average mass of 3.13 g. Copper weighs 63.546 amu (g/mol), which we found on the periodic table Here’s the game plan. We want to go from grams to atoms, but we have to always go through the mole. So, we will go from g moles atoms Example Problems 3.13 g Cu x 0.049255 mol Cu x 1 mol Cu 63.546 g Cu 6.02 x 1023 1 mol Cu = 0.049255 mol Cu = 2.97 x 1022 Cu atoms So, this is doing two types of Stoichiometry Problems. Atoms moles Grams moles Summary Slide #1 How is a mole related to atoms? What is the magic number? Avogadro’s number (NA)– 6.02 x 1023 atoms (molecules, ions, whatever)/mole When going from moles to atoms (multiply): 6.02 x 1023 atoms 1 mol When going from atoms to moles (divide): 1 mol 6.02 x 1023 atoms Summary Slide #2 How is the mole related to mass? Molar Mass For an element, it is the mass from the periodic table For compounds, you must calculate the molecular weight of the compound. Sometimes, before one can work with a mass, you have to use the density of the substance. (D=m/V or m=DV) Summary Slide #3 How is a mole related to mass? When going from moles to grams (multiply): molar mass 1 mol When going from grams to moles (divide): 1 mol molar mass Example Problems 1) 2) 3) 4) 5) 6) 7) How many moles are in 10.23 g of PO4-3? What is the mass of 6 moles of CH2O? How many ions are in 0.25 moles of Cu+2? How many moles are 8.25 x 1028 molecules of Na2CO3? How many formula units are in 6.34 g of NaCl? How many grams are in 3.4 x 1024 molecules of CH4? How many moles are in 10 mL of water (density of water = 1 g/mL)? Homework Page 251(252) – 20, 21, 23, 27, 33, 35, 36, 39