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Stoichiometry

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

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Stoichiometry

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  1. Stoichiometry The mathematics of Chemistry

  2. 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?

  3. 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

  4. How do we get that number? By using Avogadro's Number 6.02 x 1023 and using dimensionalanalysis again

  5. What is Avogadro’s Number? • It is 6.02 x 1023atoms 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?

  6. The mole is also related to molar mass • MolarMass – 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?

  7. Atomic Mass Units verses Molar Mass • The mass in grams of 1 mol of an element is numericallyequal 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

  8. 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

  9. Example Problems 1 mol Cu 3.13 g Cu x = 0.049255 mol Cu 63.546 g Cu 6.02 x 1023 0.049255 mol Cux = 2.97 x 1022 Cu atoms 1 mol Cu

  10. So, this is doing two types of Stoichiometry Problems. Atoms  moles Grams  moles

  11. 6.02 x 1023 atoms 1 mol 1 mol 6.02 x 1023 atoms Summary Slide #1How 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): • When going from atoms to moles (divide):

  12. Summary Slide #2How 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)

  13. molar mass 1 mol 1 mol molar mass Summary Slide #3How is a mole related to mass? • When going from moles to grams (multiply): • When going from grams to moles (divide):

  14. Example Problems • 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)?

  15. Homework • Page 251(252) – 20, 21, 23, 27, 33, 35, 36, 39

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