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# Applied Chapter 3.4 : Counting Atoms

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### Applied Chapter 3.4 : Counting Atoms

1. 1. Counting Atoms<br />Chapter 3.4<br />
2. 2. Objectives:<br />Compare the quantities and units for atomic mass with those for molar mass.<br />Define mole, and explain why this unit is used to count atoms<br />Calculate either mass with molar mass or number with Avogadro’s number given an amount in moles<br />
3. 3. Atomic Mass<br />Mass of an atom expressed in atomic mass units ( amu )<br />Originally used b/c the mass of proton and neutron were approximately 1.0 amu each.<br />Example: Copper – 63 62.940 amu<br /> Copper – 64 64.928 amu<br />From periodic table:<br />Copper is given atomic mass of 63.546 amu<br />This is an average of naturally occurring isotopes<br />
4. 4. Introduction to the mole<br />Mole :<br />Defined as the number of atoms in exactly 12 grams of carbon – 12. <br />SI base unit for amount of substance<br />Used as Counting unit<br />Instead of 12 eggs, we say 1 dozen eggs<br />We use 1 mol of carbon or 2 mol of iron<br />
5. 5. Molar mass<br />Mass in grams of ONE mole.<br />Units – g/mol<br />Find from periodic table<br />Oxygen – 15.9994 amu<br />Round to 16.00 amu - USE two decimal places<br />So the molar mass of oxygen is 16.00 g/mol<br />Find the molar masses for<br />Aluminum<br />Uranium<br />Chlorine<br />26.98 g/mol<br />238.03 g/mol<br />35.45 g/mol<br />
6. 6. Avogadro’s Number<br />Number of particles in 1 MOLE of a substance<br />6.022 x 1023<br />60 220 000 000 000 000 000 000<br />How big is this number?<br />Entire population of Earth – 6 billion<br />6.00 x 109 or 6 000 000 000<br />
7. 7. Determine Mass from MOles<br />Determine mass in grams of 3.50 mol of copper<br /> 3.50 mol<br />Step 1:<br />Step 2:<br />Step 3:<br />Write what is given<br />Cancel out units<br />Calculate<br />g<br />63.55<br />x<br />=<br />222 g<br />mol<br />1<br />* Multiply everything on top<br />From periodic table<br />* Divide by everything on bottom<br />
8. 8. Practice Problems<br />What is the mass in grams of 1.00 mol of uranium?<br />What is the mass in grams of 00.50 mol of uranium?<br />Calculate the number of moles of 0.850 g of hydrogen atoms. What is the mass in grams of 0.850 mol of hydrogen atoms?<br />Calculate the mass in grams of 2.3456 mol of lead. Calculate the number of moles of 2.3456 g of lead.<br />238 g<br />1.2 g<br />0.84 mol<br />and 0.86 g<br />486.0 g<br />and 0.01132 mol<br />
9. 9. Determine number of atoms from moles<br />Determine the number of atoms in 0.30 mol of fluorine atoms<br /> 0.30 mol<br />Step 1:<br />Step 2:<br />Step 3:<br />Write what is given<br />Cancel out units<br />Calculate<br />6.02 x 1023<br />atoms<br />x<br />=<br />1.8 x 1023 F atoms<br />mol<br />1<br />* Multiply everything on top<br />Avogadro’s Number<br />* Divide by everything on bottom<br />
10. 10. Practice Problems<br />How many atoms are in 0.70 mol of iron?<br />How many moles of silver are represented by 2.888 X 1023 atoms?<br />How many moles of osmium are represented by 3.5 x 1023 atoms?<br />4.2 x 1023 atoms<br />0.4796 mol<br />0.58 mol<br />