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# Chapter 7.3 : Using Chemical Formulas

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### Transcript of "Chapter 7.3 : Using Chemical Formulas"

1. 1. Using Chemical Formulas<br />Chapter 7.3<br />
2. 2. Objectives<br />Calculate the formula mass or molar mass of any given compound.<br />Use molar mass to convert between mass in grams and amount in moles of a chemical compound.<br />Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound.<br />Calculate the percentage composition of a given chemical compound.<br />
3. 3. Formula Masses<br />Defined as: of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented.<br /><ul><li>Find the formula mass of potassium chlorate, KClO3.</li></ul>K 1 x 39.10 amu = <br />Cl 1 x 35.45 amu =<br />O 3 x 16.00 amu = _ <br />39.10 amu<br />35.45 amu<br />48.00 amu<br />122.55 amu<br /><ul><li>Find the formula mass of sulfuric acid, H2SO4.</li></ul> 2.02 amu<br />H 2 x 1.01 amu = <br />S 1 x 32.07 amu =<br />O 4 x 16.00 amu = _ <br />32.07 amu<br />64.00 amu<br />98.09 amu<br />
4. 4. Molar Mass<br />Defined as: mass in grams of one mole, or approximately 6.022 x 1023 particles.<br /><ul><li>Mass of one mole is the mass of 6.022 x 1023 particles.
5. 5. Formula mass is the mass of one atom
6. 6. Although different meaning :
7. 7. Molar mass and formula mass are numerically equal
8. 8. Find the molar mass of barium nitrate, Ba(NO3)2.</li></ul>137.33 g/mol<br />Ba 1 x 137.33 g/mol = <br />N 2 x 14.01 g/mol =<br />O 6 x 16.00 g/mol = _ <br />28.01 g/mol<br />96.00 g/mol<br />261.35 g/mol<br /><ul><li>Find the molar mass for: </li></ul>Answers:<br />150.17 g/mol<br />Al2S3<br />B) Ba(OH)2<br />B) 171.35 g/mol<br />
9. 9. Molar Mass as a conversion<br />Amount of compound (moles)<br />Mass of a compound (grams)<br />Number of molecules or formula units<br /> Molar mass<br />6.02 x 1023<br />÷<br />x<br /> 6.02 x 10 23<br /> Molar mass<br />÷<br />x<br />
10. 10. Molar Mass as a conversion<br />Practice problems<br />What is the mass in grams of 2.50 mol of oxygen gas?<br />Step 3:<br />Step 1:<br />Step 2:<br />Cancel units<br />Calculate<br />Write what is given<br />32.00 g<br />80.0 g O2<br />2.50 mol O2<br />=<br />X<br />1 mol<br /><ul><li> Ibuprofen, C13H18O2, is the active ingredient in many nonprescription pain relievers. Its molar mass is 206.29 g/mol.</li></ul>If the tablets in a bottle contain a total of 33 g of ibuprofen, how many moles of ibuprofen are in the bottle<br /> 1 mol<br />33 g<br />=<br />0.16 mol C13 H18O2<br />X<br />206.29 g<br />
11. 11. How many molecules of ibuprofen are in the bottle?<br /> 6.022 x 1023 molecules<br />o.16 mol<br />=<br />9.6 x 1022 molecules<br />X<br /> 1 mol<br />More Practice problems<br />How many moles of the compound are there in 6.60 g (NH4)2SO4?<br />How many molecules are there in 25.0 g H2SO4?<br />What is the mass in grams of 6.25 mol of copper(II) nitrate<br />Answer: 0.0500 mol<br />Answer: 1.53 x 1023 molecules<br />Answer: 1170 g<br />
12. 12. Percentage composition<br />Useful in determining the percent by mass of each element in a compound<br />1. Find the percent composition of copper(I) sulfide, Cu2 S.<br />First: find the total molar mass<br />Cu 2 x 63.55 g = 127.1 g Cu<br />S 1 x 32.07 g = 32.07 g S<br />159.2 g Cu2S<br />Second: find the percent of each<br />127.1 g Cu<br />X 100<br />= 79.84 % Cu<br />159.2 g Cu2S<br />32.07 g S<br />X 100<br />= 20.14 % S<br />159.2 g Cu2S<br />
13. 13. More Practice: percent composition<br />Find the mass percentage of water in sodium carbonate decahydrate, Na2CO3 10H2O, which as a molar mass of 286.14 g/mol.<br />Find the percentage composition of <br />PbCl2<br />Ba(NO3)2<br />10 mol H2O<br />x 18.02 g H2O<br /> 1 mol H2O<br />= 180.2 g H2O<br />180.2 g H2O<br />x 100<br />= 62.98 % <br />286.14 g Na2CO3 10 H2O<br />Answer: 74.51 % Pb, 25.49 % Cl<br />Answer: 52.55 % Ba, 10.72 % N, 36.73 % O<br />
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