What is a mole in chemistry? What is Avogadro’s Number? The SI unit for measuring the The atomic mass of one atom of carbon-12 is 12 amu. ____________________________ Avogadro found that ___________ ____________________________ of carbon-12 had ______________ atoms. The unit symbol is _____________ __________________ became known as ____________________ One mole is equal to ____________________________ ____________________________ which equals one mole! ____________________________ That works for everything! Since particles of matter are so small, we can’t count them even if we could count that high. If we have one mole of calcium, how many atoms of calcium do we have? Moles are used to convert mass in _________________ to ____________________________ If we have 6.02x1023 atoms of potassium, how many moles do we have? Particles of Matter Particles of Matter continued Particles of Matter continued Formula Unit: Representative Atom: Representative particle of Molecule: Representative particle particle of ___________________ ____________________________ of __________________________ ____________________________ ____________________________ ____________________________ Formula units are described by Atoms are indicated by an Molecules are described by ____________________________ ____________________________ ____________________________ Examples: Examples: Examples: NaCl represents one formula unit of ________________________ H O represents one water molecule 2 commonly called table salt. How many H atoms? How many atoms of Na? How many O atoms? How many atoms of Cl? How many total atoms? Ion: Representative particle of How many total atoms? ____________________________ Na(HCO3) represents one formula ____________________________ C H O represents one sugar 12 22 11 unit of ______________________ Ions are indicated by an molecule common name is baking soda. ____________________________ How many C atoms? How many Na atoms? ____________________________ How many H atoms? How many H atoms? Examples: How many O atoms? How many C atoms? How many total atoms? How many O atoms? How many total atoms? How to Determine Molar Mass Molar mass of an element is ________________ ___________________________ of the element from the periodic table, but the units are different. The unit for molar mass is _____________________ The molar mass of potassium is ______________ zinc is __________________________________ Oxygen can be rounded to __________________ Molar mass of a compound requires a ____________ _________________; this is often called formula mass. The mass of _________________________ in the formula is _____________ together in the ratios as of the _____________________; the unit is in _____________________________. Let’s do examples inside using the mole map! How are molecular and empirical formulas determined from a 3) Find the empirical formula of the compound by finding the ratio of the number of moles of elements. percent composition calculation? Review: Empirical formulas are reduced versions of the An empirical formula is a chemical formula with the lowest molecular formula. In a practical sense, this means that we should divide the number of moles of each element by the whole-number ratio of elements in a compound. smallest answer for number of moles. Since the smallest A molecular formula is the actual chemical formula of a number is “7.14 moles”, we’ll divide both values by 7.14. compound. carbon: 7.14 ÷ 7.14 = 1 Empirical formulas are reduced versions of the molecular hydrogen: 14.3 ÷ 7.14 = 2 formula. For example, a compound that has an empirical formula of CH2O may have a molecular formula of C2H4O2, Empirical formula: C3H6O3, C4H8O4, etc. Handy hint: If the problem gives you the empirical Steps 1-3 for Calculating Empirical Formulas and Steps 4-5 for formula, you can start at the next step! Calculating Molecular Formulas 4) Divide the molar mass of the compound in the problem by Once you have a percent composition of a chemical compound, the molar mass of the empirical formula. it’s possible to figure out the molecular formula. Here’s how, For our compound, the molar mass of the compound is using the example of a compound with a molar mass of 28 grams/mol in which the percent composition of the components For the empirical formula, CH2, the molar mass is are as follows: o C: 85.7% Divide as instructed in step 4 above o H: 14.3% 5) Multiply the subscripts in the empirical formula by the 1) Assume you have 100 grams of the chemical. This serves to number you found in step 4 to find the molecular formula. convert the percentages into grams. In our example, we now have NOTE: Sometimes the empirical formula and molecular formula are 2) Figure out how many moles of each element you have in the the same. compound. What does the percent composition of a compound represent, and how is it calculated? The percent composition of a compound represents the percentage of each element in a compound by mass. o Percent composition is calculated by dividing the mass of a single element in one mole of a compound by the molar mass of the compound and multiplying by 100 to make a percentage. o Example using water, what is the percent composition of H and O? o o H2 mass o O mass .