The Mole and Avogadro’s Number Molar Mass Finding n Finding the # of atoms Working with formulas - Practice

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We sometimes give a name to a specific amount Pair = 2 Dozen = 12 Can you think of any more?????

The Mole….. We need a relationship between the mass of a sample of an element/compound and the number of atoms/molecules in that sample For this, we use the MOLE ____________

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The atomic mass (amu) = molar mass (grams/mol) The Molar mass of anything is the mass of 1 mole of that thing in grams Coins, chickens, computers, students, etc. ____________ For any element The atomic mass (amu) = molar mass (grams/mol)

What is the mass of one mole of: C Hg Cu Fe

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One of THE formulas in Chemistry n = m M n = number of moles m = mass of the sample M = molar mass

Practice Questions 1. How many moles of Na are in 42 g of Na? 3.    How much does 2.18 mol of Cu weigh? 4.    What is the ……………. n = m M

The Number of Atoms How do you find the number of atoms? n=m/M What does n represent? __________ What is a mole?

Easier Remember the mole represents a number, a really big number but it’s just a number. The ………….. 1) How many dozen eggs do you have if you have 4 eggs? ____________ ___________ 2) How many dozen eggs do you have if you have 18 eggs? 3) How many dozen eggs do you have if you have 12 eggs?

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Check Your Understanding: Find the # of particles/atoms 1.    How many atoms are ……………? 2.    How many atoms are in 36 g of bromine? 3.    How many moles are in …………….? n = # of particles 6.02x1023

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Molar Mass The molar mass of a compound is found by adding together the molar masses of all of its elements, taking into account the number of moles of each element present. Recall: atomic mass = molar mass if there is 1 mole of substance ___________ e.g. H2 = 1.008 + 1.008 (we don’t round!) = 2(1.008) = 2.016 amu If there is 1 …………..

Check Your Understanding: What is the molar mass? H2O CO2 CO C6H12O6

Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. + 2 x 16.00 amu SO2 64.07 amu ____________ 1 molecule SO2 = 64.07 amu 1 mole SO2 = 64.07 g SO2

How many H atoms are in 72.5 g of C3H8O ? Step 1 – Find the number of Molar Mass of C3H8O

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How many H atoms are in 72.5 g of C3H8O ? Step 3 – Find the number of atoms of H using nH